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ICSE Class 8 Question Bank 2024 : Chemistry : Icse class 8

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8 Chemistry The Science Orbit Teacher s Manual R (An imprint of New Saraswati House (India) Pvt. Ltd.) New Delhi-110002 (INDIA) R (An imprint of New Saraswati House (India) Pvt. Ltd.) Second Floor, MGM Tower, 19 Ansari Road, Daryaganj, New Delhi-110002 (India) Phone : +91-11-43556600 Fax : +91-11-43556688 E-mail : delhi@saraswatihouse.com Website : www.saraswatihouse.com CIN : U22110DL2013PTC262320 Import-Export Licence No. 0513086293 Branches: Ahmedabad (079) 22160722 Bengaluru (080) 26619880, 26676396 Bhopal +91-7554003654 Chennai (044) 28416531 Dehradun 09837452852 Guwahati (0361) 2457198 Hyderabad (040) 42615566 Jaipur (0141) 4006022 Jalandhar (0181) 4642600, 4643600 Kochi (0484) 4033369 Kolkata (033) 40042314 Lucknow (0522) 4062517 Mumbai (022) 28737050, 28737090 Nagpur +91-7066149006 Patna (0612) 2275403 Ranchi (0651) 2244654 First published 2018 TM Code: 2017007000109 Published by: New Saraswati House (India) Pvt. Ltd. 19 Ansari Road, Daryaganj, New Delhi-110002 (India) The moral rights of the author has been asserted. Reserved with the Publishers Publisher s Warranty: The Publisher warrants the customer for a period of 1 year from the date of purchase of the Book against any Printing/Binding defect or theft/loss of the book. Terms and Conditions apply: For further details, please visit our website www.saraswatihouse.com or call us at our Customer Care (toll free) No.: +91-1800-2701-460 Jurisdiction: All disputes with respect to this publication shall be subject to the jurisdiction of the Courts, Tribunals and Forums of New Delhi, India Only. All rights reserved under the Copyright Act. No part of this publication may be reproduced, transcribed, transmitted, stored in a retrieval system or translated into any language or computer, in any form or by any means, electronic, mechanical, magnetic, optical, chemical, manual, photocopy or otherwise without the prior permission of the copyright owner. Any person who does any unauthorised act in relation to this publication may be liable to criminal prosecution and civil claims for damages. Printed at: Vikas Publishing House Pvt. Ltd., Sahibabad (Uttar Pradesh) Product Code: NSS2TSO086CHEAA17ICN This book is meant for educational and learning purposes. The author(s) of the book has/have taken all reasonable care to ensure that the contents of the book do not violate any copyright or other intellectual property rights of any person in any manner whatsoever. In the event the author(s) has/have been unable to track any source and if any copyright has been inadvertently infringed, please notify the publisher in writing for any corrective action. Preface The purpose of The Science Orbit series (3 to 8) teacher s resource pack is to empower teachers to make classroom teaching a holistic experience. It will enable teachers to explain the chapters in the most effective way, which will not only impart knowledge, but also ignite interest in the minds of young learners towards the subject. A wide array of resources complement these manuals, which makes learning an interesting process instead of a routine chore. Teacher s Manual Teacher s Manual resources have been carefully prepared with an aim to make the process of teaching and learning interesting and intriguing for the teachers and learners alike. It comprises detailed lesson plans and answers to the coursebook along with solved worksheets and model test papers. These have been prepared keeping in mind the explanation of the concepts and the level appropriateness of the topics. Easily available teaching aids are used to make teaching and learning an interactive and lucid process. The lesson plans give a topic-wise explanation of each chapter. Its components are: Warm-up section guides the teacher to start the topic in an interesting way. Learning objectives give the list of measurable aims of each chapter, which should be achieved after teaching the chapter. Concept explanation gives a detailed method of explaining the important concepts of the chapter using various teaching aids. Reinforce section allows the teacher to check the progress of the concepts learned by the students with the help of textual questions and worksheets and allows them to revisit and revise the concepts, if required. Explore section helps the learners to do various activities, often taking them beyond their classroom learning. App-based Digital Store Digital offerings comprise digital resource embedded e-book, 2D and 3D animations, videos, interactive activities, slideshows, educational games, test generator and teacher s manual. Web Support The web support consists of worksheets, model test papers, and answers to worksheets and model test papers. These would help teachers in assessing students on the concepts taught in the class. Contents 1. Matter 5 2. Physical and Chemical Changes 14 3. Elements, Compounds and Mixtures 23 4. Atomic Structure 32 5. Language of Chemistry 41 Model Test Paper 1 54 6. Chemical Reactions 56 7. Hydrogen 68 8. Water 77 9. Carbon and its Compounds 87 Model Test Paper 2 101 1 Matter Learning Objectives Students will be able to: understand matter and its properties know The Kinetic Molecular Theory of Matter learn different states of matter understand the Law of Conservation of Mass Warm-up States of Matter Start the chapter by asking questions related to atoms, molecules, and various states of matter. Let students think about the molecular arrangement of different states of matter. Now, ask them to complete the exercise given in the Warm-up section. Explain to the students the behaviour of different states of matter on the basis of the kinetic molecular theory. In case of solids, where molecules are closely packed with maximum interparticle force of attraction, kinetic energy is the least. Let them understand for liquids also in which molecules are less closely packed with less intermolecular force of attraction. So, the particles do not have enough kinetic energy. Concept Explanation The Kinetic Molecular Theory of Matter and its Postulates Explain to the students about the Kinetic Molecular Theory of Matter. The most obvious question related to this is that why matter undergoes a change of state? According to this theory, matter is composed of particles, either atoms or molecules, which are in continuous motion and thus possess kinetic energy. The energy of the particles increases with the increase in temperature. Also explain to the students that pressure exerted by a liquid or a gas is due to the collision of molecules with each other or within the walls of the container. While in the case of gases, particles are far apart and have enough kinetic energy to overcome the least force of attraction between the particles. Properties of Matter On the basis of the above theory, explain to the students various properties of matter. Solids have a xed shape and volume, liquids have no xed shape but have xed volume, while gases have no xed shape and volume. 5 Density Law of Conservation of Mass Next, explain to the students that density (which is mass per unit volume) is more in solids as compared to liquids and gases. Explain to the students the law of conservation of mass which states that in a chemical reaction, the total mass of the reactants is equal to the total mass of the products. Change of State Due to Heat Let students understand the change of state due to the effect of heat. All the three states expand on heating. When a solid is heated, the kinetic energy increases and the particles vibrate such that the structure of solid changes. The temperature at which a solid changes to a liquid is known as melting point. Further, explain to the students that if this liquid is further heated, it changes to gas and this temperature is known as boiling point. The reverse process also takes place on cooling. ACTIVITY: Take solutions of sodium sulphate and barium chloride in an apparatus. Weigh them before mixing. After mixing, a precipitate of barium sulphate and solution of sodium chloride is formed. Now on weighing this, we observe that: Change of State Due to Matter To reinforce, ask the students to read the Summary and Glossary sections and do the Exercises and Learning Zone sections from the textbook. Help students develop skills (research and thinking) given in the Skills for Life section in the chapter. Total mass of apparatus = Total mass of apparatus + + Reactants Products Reinforce Explain to the students the effect of pressure on change of state. Solids show little compression. On applying high pressure on a gas, the attractive forces becomes strong and it condenses to the liquid state. Make students aware of LPG and CNG which are in the liquid state under pressure and change to gas when pressure is released. Explore Ask students to do the Learn by Doing section given at the end of the chapter. To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. 6 Worksheet 1 1. Give one word for the following. a. Mass per unit volume _________________. b. Anything that has mass and occupies space _________________. c. State of matter which has neither a de nite shape nor a xed volume __________. d. The space between the particles of matter _________________. e. Force present in the atoms or molecules of matter _________________. 2. Which state of matter has the minimum force of attraction between the particles? Why? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 3. Explain the law of conservation of energy. Give one example. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 4. Explain the change of state when gas molecules are compressed. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 5. Differentiate between. a. Melting point and boiling point. _____________________________________________________________________ _____________________________________________________________________ b. Solid and gas. _____________________________________________________________________ _____________________________________________________________________ 7 Worksheet 2 1. Fill in the blanks. a. In gases, the collisions between molecules are perfectly _________________. b. A change of state of matter occurs due to a change in the _________________ of the particles. c. Matter can neither be _________________ nor _________________ in a chemical reaction. d. The decreasing order of the intermolecular forces of attraction in different states of matter is _________________. e. _________________ proposed the law of conservation of mass. 2. Look at the gures and answer the following questions. (i) (ii) (iii) a. Identify the three states of matter. _____________________________________________________________________ b. De ne (ii) and (iii) in terms of interparticle space and interparticle force of attraction. _____________________________________________________________________ _____________________________________________________________________ c. Which state of matter is the most dense? _____________________________________________________________________ _____________________________________________________________________ d. What happens when particles of (a) are heated? _____________________________________________________________________ _____________________________________________________________________ 8 Answers to Coursebook PART I A 1. (b) 2. 5. (d) 6. B 1. Elastic 4. Gases C 1. True 4. False D 1. (c) 2. 5. (b) (a) (d) 2. 5. 2. 5. (d) 3. (b) down. At this point, the solid melts into liquid. The temperature at which this change from solid to liquid happens is called the melting point. The temperature may vary for different solids, so some may have high and some may have low melting point. At the moment of melting, the average kinetic energy of the molecules does not change. The heat is used to break the bonds between the solid molecules as they turn into a liquid phase. 4. (d) Increases 3. Lavosier Chemical False 3. False False 3. (e) 4. (a) PART II A 1. The kinetic theory of matter was rst proposed by Bernouli. 3. The reaction obeys the law of conservation of mass as in this chemical reaction, the total mass of the reactants (water) is equal to the total mass of products(hydrogen and oxygen). 2. Size and shape, density, effect of heat and pressure are the factors on which behaviour of gases depend. 4. The upper surface of water absorbs heat and light energy and the molecules on upper surface gain energy and overcome the binding force. Evaporation is known as surface phenomena because molecules of water present on the surface of liquid are bonded weakly as compared to inner molecules and when temperature increases, hydrogen bond of water molecules breaks. Due to this water molecules tend to evaporate, so that s why it is called as surface phenomena. 3. One gram of nitrogen will have more volume as compared to one gram of hydrogen. 4. Liquids generally expand on heating. The increased kinetic energy of the particles increases the interparticle space, as a result, the liquid expands in size, thus the volume of a liquid increases when heated. B 1. Different solids and liquids require different amounts of energy to get transformed into the liquid state and the gaseous state, respectively. The difference is due to the different interparticle space and interparticle force. The kinetic energies of the particles in different solids and liquids are also different. All the gases show almost the same behaviour at a xed temperature and pressure. In gases, the interparticle force (attraction) is almost negligible and interparticle spaces are very large. Change in temperature and pressure causes change in the state. C 1. The postulates of the Kinetic Molecular Theory of Matter are as follows. Matter is composed of a very large number of tiny, invisible particles which could be atoms or molecules. Between the particles of matter there exists a vacant space called the interparticle space. The interparticle space is very little in solids, more in liquids and still more in gases. Due to the heat energy, particles of matter are in continuous motion, so they possess kinetic energy. The kinetic energy of the particles increases with an increase in temperature. 2. When a solid is heated, the kinetic energy of particles increases accordingly. At a certain temperature, the particles vibrate so much that their ordered structure breaks 9 c. 2Mg + O2 2MgO The molecules collide with each other and with the walls of the container. The inter particle collisions are perfectly elastic, i.e., there is no loss or gain of energy during collisions. Particles move with the same speed after colliding with each other. The particles of the matter may also collide with the particles of any other matter they come in contact with. 4. a. If a liquid is heated, the kinetic energy of the particles increases and the particles start to move faster and further apart. At a certain temperature, the particles break free of one another and the liquid turns into a gas. This is the boiling point. The boiling point of a substance is always the same; it does not vary. The pressure exerted by a liquid or a gas is due to the force exerted by the particles on the walls of the container when they collide. The more the number of collisions on the walls, the higher the pressure. 2. Take 5 mL of sodium sulphate solution in a measuring cylinder and pour it into a conical ask. Take 5 mL of barium chloride solution in another measuring cylinder and pour it into a 10 mL test tube and then put this test tube which is tied to a thread, in the ask carefully, so that the two solutions do not mix with each other. Put a cork on the mouth of the test tube so that the thread holding the test tube is held rmly in place. Now, carefully weigh the conical ask on a weighing balance and note the reading to get the mass of the conical ask and the substances. Now, tilt and twist the ask so that barium chloride solution mixes with the sodium sulphate solution. Reaction involved isBaCl2 + Na2SO4 BaSO4 (s) + 2NaCl It will be observed that a white insoluble solid (precipitate) of barium sulphate is formed along with a solution of sodium chloride. Wait for 10 minutes to complete the reaction and the solid formed to settle down. Weigh the contents again and note the reading. Thus, b. When a solid is heated, the particles of solid start to vibrate faster. The kinetic energy of particles increases accordingly, as their motion increases. At a certain temperature, the particles vibrate so much that their ordered structure breaks down. At this point, the solid melts into liquid. The temperature at which this change from solid to liquid happens is called the melting point. c. If heat energy is taken out from a gas (e.g., by cooling), the particles of the gas lose some of their kinetic energy and the matter becomes liquid. This process is called condensation. D 1. The pressure law states that for a constant volume of gas in a sealed container, the temperature of the gas is directly proportional to its pressure. This can be easily understood by visualising the particles of gas in the container moving with a greater energy when the temperature is increased. Total Mass of apparatus + Reactants = Total mass of apparatus + Products. Hence, the law of conservation of mass is veri ed. 3. a. CaCO3 CaO + CO2 b. 2Na + 2H2O 2NaOH + H2 10 2. During melting, the heat being added to a substance goes into breaking down the crystal lattice or breaking apart the molecules , not into raising the temperature. During the phase change all the molecules continue to have the same kinetic energy, and therefore the temperature remains constant. The same thing happens at the boiling point. The energy goes into breaking the intermolecular bonds, but the average kinetic energy stays constant and so does the temperature until all of the bonds are broken and the substance is in the vapour state. carefully, so that the two solutions do not mix with each other. Now, the conical ask is weighed on a weighing balance and reading is noticed to get the mass of the conical ask and the substances. On tilting and twisting the ask, barium chloride solution mixes with the sodium sulphate solution, a white insoluble solid (precipitate) of barium sulphate is formed along with a solution of sodium chloride. 3. Matter can neither be created nor destroyed in a chemical reaction. However, it may change from one form to another in the process. There is no change in the mass during a chemical reaction as in a chemical reaction the total mass of the reactants is equal to the total mass of products. 4. Solids are non-compressible as the particles of the matter are closely packed, and have a well-de ned order in the arrangement. Also, the interparticle force of attraction between the molecules is the maximum and hence are non-compressible. 5. The increased kinetic energy of the particles in the case of gases increases the interparticle space which is already more as compared to liquids, as a result, the gas expands more in size. E 1. The temperature at which solid changes to liquid is called the melting point. At the moment of melting, the average kinetic energy of the molecules does not change. On the other hand, freezing is the process by which a liquid forms into a solid on cooling. The particles of the liquid lose some of their kinetic energy and become solid. 2. Interparticle space is the space between the particles of matter; the particles can be atoms or molecules, whereas interparticle force is the force of attraction or repulsion between the atoms or molecules of which the matter is made. In solids, intermolecular space is almost absent and force of attraction is maximum among them. BaCl2 + Na2SO4 BaSO4(s) + 2NaCl The contents are weighed again Total Mass of apparatus + Reactants = Total mass of apparatus + Products 2. a. In gases, the interparticle force (attraction) is almost negligible and interparticle spaces are very large. When pressure is applied, collision occurs among them and with the walls of the container, the gas molecules move towards each other. b. In B c. The particles have more kinetic energy where the interparticle space is more. If more pressure is applied, molecules will move closer together. If compressed enough, the substance will change into a more compact phase. The average kinetic energy of a gas particle is directly proportional to the temperature. An increase in temperature increases the speed at which the gas molecules move. 3. a. When wood burns much of the mass leaves as smoke. The mass of the ashes plus the mass of the smoke from the burning wood equals the original mass of the wood. LEARNING ZONE Picture based questions 1. a. Barium chloride solution b. Sodium sulphate solution c. Sodium sulphate solution is poured it into a conical ask. Barium chloride solution is poured into a test tube (which is tied with a thread) and then kept in the ask 11 Ash is only one of the products of the reaction, and can thus weigh less than the original wood. To ensure that conservation of mass is not violated, we have to capture all the gas which was released in the reaction, as well as record the mass of gas which reacted. It may seem as though burning destroys matter, but the same amount, or mass, of matter still exists as before. When wood burns, it combines with oxygen and changes not only to ashes, but also to carbon dioxide and water vapour. The gases oat off into the air, leaving behind just the ashes. Suppose we had measured the mass of the wood before it burned and the mass of the ashes after it burned. Also suppose we had been able to measure the oxygen used by the re and the gases produced by the re. We nd that the total mass of matter after the re would be the same as the total mass of matter before the re. b. Yes, when wood burns much of the mass leaves as smoke. The mass of the ashes plus the mass of the smoke from the burning wood equals the original mass of the wood. Think and answer 1. In the LPG (Lique ed Petroleum Gas) cylinders found in the kitchen, the petroleum gas exist in liquid state under pressure. The liquid expands and emerges out as gas from the cylinders only when the pressure is released (e.g., by opening the knob). 2. The answer depends upon various factors associated with the nature of the liquid or solid. Factors like density and temperature are to be considered. The density of the liquid state is less than that of the solid state for the same substance, and density is inversely proportional to the volume of a material. The liquid state of a substance occupies more volume than the solid state. Answers to Worksheets WORKSHEET 1 5. a. The temperature at which solid changes to liquid state is called the melting point. At the moment of melting, the average kinetic energy of the molecules does not change. The heat is used to break the bonds between the ice molecules as they turn into a liquid phase. If the heating of the liquid is continued further, the particles start to move faster and further apart. At a certain temperature, the particles break free of one another and the liquid turns into a gas. This is the boiling point. The boiling point of a substance is always the same; it does not vary. 1. a. Density b. Matter c. Gas d. Interparticle Space e. Interparticle force 2. Gases have the minimum force of attraction because the atoms or the molecules are loosely packed with large interparticle space between them. So the force of attraction is negligible. 3. It states that in a chemical reaction, the total mass of the reactants is equal to the total mass of products i.e. there is no change in the mass during a chemical reaction b. In case of solids, the particles of the matter are closely packed, hence, the inter particle force of attraction between the molecules is the maximum. In the case of gases, the particles are far apart from each other and the force of attraction between them is negligible. Example: BaCl2 + Na2 SO4 BaSO4 + 2NaCl 4. If we increase the pressure on a gas, its molecules are brought in close contact with each other. The attractive forces eventually become strong enough to hold the molecules close together, and the gas condenses into the liquid state. WORKSHEET 2 12 1. a. Elastic b. Kinetic energy c. Created, destroyed d. Solid > liquid > gas e. Lavosier 2. a. Solid, Liquid, Gas b. In case of liquids, the particles of the matter are less closely packed but more closely packed than in gases. Hence, the inter particle force of attraction between the molecules is more than that in gases. Therefore, the particles of the liquid are free to move about within the liquid. They do not have enough kinetic energy to overcome the inter particle forces. That is why a small amount of additional energy can make them break away from the interparticle forces. In case of gases, the particles of 13 matter are not packed closely. They are placed far away from each other. The interparticle attraction force between the particles is negligible. The particles of gases are free to move in any direction and in all the available space. They have enough kinetic energy to overcome interparticle attraction forces that are almost negligible. c. Solids d. When a solid is heated, the particles of solid start to vibrate faster. The kinetic energy of particles increases accordingly, as their motion increases. At a certain temperature, the particles vibrate so much that their ordered structure breaks down. At this point, the solid melts into liquid. 2 Physical and Chemical Changes Learning Objectives Students will be able to: explain the various types of changes differentiate between physical and chemical changes categorise physical and chemical changes understand that evaporation, boiling, condensation, freezing, melting and sublimation are physical changes understand that fermentation, rusting, respiration, cooking, burning, digestion the chemical changes Warm-up Interact with the students asking them about changes around them like growth of plants, stretching of rubber band, burning of crackers, etc. Make them analyse whether the above changes are desirable or undesirable, natural or man-made, physical or chemical, etc. Concept Explanation Changes A Review Give a quick review to the students on the work done in the previous classes. Make them understand different types of changes. Desirable and undesirable changes, periodic and non-periodic changes, reversible and irreversible changes, slow and fast changes and natural or man-made changes. Explain to the students the difference between desirable and undesirable change, periodic and non-periodic changes, reversible and irreversible changes, slow and fast changes and natural or man-made changes. Give some examples for better understanding. Physical and Chemical Changes and Exothermic and Endothermic Changes Explain to the students the difference between physical and chemical changes. When chemical composition of a substance remains the same, it is a physical change and when it changes, it is called a chemical change. Let students know that the change in which energy is released in the form of heat, is called exothermic change and that which absorbs energy is called endothermic change. To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. 14 Categorising Physical Changes Explain to the students the process of evaporation, which is a physical change. Let them understand how evaporation is affected by factors like surface area, humidity, motion of air, temperature or air-pressure. It increases with increase in surface area, motion of air, temperature. Explain to the students the difference between evaporation and boiling. Let students grasp that condensation and freezing are reversible and exothermic physical changes. Explain to them that sublimation is reversible and endothermic. Categorising Chemical Changes Explain to the students that chemical changes such as fermentation, rusting, cooking, digestion are endothermic chemical changes while respiration and burning are exothermic chemical changes. To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. Reinforce To reinforce, ask the students to read the Summary and Glossary sections and do the Exercises and Learning Zone sections from the textbook. Help students develop skills (research and thinking) given in the Skills for Life section in the chapter. Explore Ask students to do the Learn by Doing section given at the end of the chapter. 15 Worksheet 1 1. Classify the changes involved in the following process as physical or chemical changes. a. Respiration _________________ b. Photosynthesis _________________ c. Dissolving of sugar in water _________________ d. Burning of coal _________________ e. Melting of wax _________________ f. _________________ Digestion of food g. Fermentation _________________ h. Melting of chocolate _________________ 2. Explain why rusting of iron objects is faster in coastal areas than in deserts. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 3. Burning of wood and cutting it into small pieces are considered as two different types of changes. Explain. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 4. When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 16 Worksheet 2 1. Fill in the blanks. a. When carbon dioxide is passed through lime water, it turns milky due to the formation of _________________. b. In a _________________ change, the original substance can be brought back by reversing the process. c. Energy is _________________ in the formation of curd from milk. d. Large crystals of pure substance are obtained by _________________. e. Lighting of an electric bulb is _________________ change. f. Magnesium burns in air to give _________________. 2. In the following boxes, add a reverse arrow wherever a change is physical and can be reversed. Baby Whole chalk piece Ice Broken chalk piece Water Cold water Paper Hot water Fresh bread Burnt Paper Child Unripe mango Ripe mango Rotten bread 3. A fraction of ship s iron has to be replaced every year. Explain. ________________________________________________________________________ ________________________________________________________________________ 4. Identify the type of change and state whether energy is absorbed or evolved in each of the following: burning of a candle; lighting of a bulb; preparation of food by green plants; volcanic eruption; lightning ________________________________________________________________________ ________________________________________________________________________ 17 Answers to Coursebook PART I A. 1. (b) 2. (c) 3. (d) 4. (a) 5. (c) B. 1. Physical 2. Periodic 3. Evaporation 4. Desirable 5. Endothermic C. 1. Evaporation 2. Cutting of grass 3. Condensation 4. Fermentation of sugar into alcohol, rusting of iron 5. Burning of paper, candle D. 1. False 2. False 3. True 4. False 5. False 6. False 7. True 8. True E. 1. Bursting of re crackers 2. Boiling water 3. Boiling water 4. Burning 5. Rainfall F. 1. Rusting 2. Fermentation 3. Dissolving 4. Condensation 5. Sublimation temperature and air pressure. 3. Boiling or freezing of water, making sugar or salt solution in water. 4. Melting of wax is a physical process as it results in the state transition of wax from a solid to a liquid, no new substance is formed. 5. When paper is burnt, it combines with oxygen to form ash and smoke. Chemical composition of ash is different from paper. Thus, this is a chemical change because new substances are formed. B 1. a. Periodic change- Changes that occur repeatedly after regular intervals of time and whose occurrence can be predicted are called periodic changes. PART II A 1. A change in which the chemical composition of a substance remains the same is called a physical change. No new substance is formed. A physical change is often easy to reverse. For example, the change of ice into water; when water cools, it converts into ice again. 2. Evaporation is affected by Surface area, humidity/moisture, motion of air, 18 Example: Movement of the pendulum and the hands of clocks. Their movement is xed. b. Changes that are useful to mankind are said to be desirable changes. Examples: Curdling of milk, cooking of food, etc. 2. Boiling of eggs is an example of a chemical change, because the chemical properties have been altered. The heat causes the egg s protein to change permanently in texture and in appearance and we cannot get back the original egg. On the other hand, boiling of water is a physical change as it is reversible and no new substance is formed. 3. a. Photosynthesis is a natural change as it occurs naturally on its own. Leaves take in CO2 and water in the presence of sunlight to form food in green plants. b. Cooking food is not a natural change, it is a desirable change that is man-made. 4. a. Bursting of crackers, souring of milk b. Evaporation, condensation 5. Condensation is the change of state of matter from the gas phase to the liquid phase. It can be slow or fast. As the condensation process gives out heat, it is an exothermic change. Thus, it is an exothermic, reversible and desirable physical change. 6. Burning is a chemical change in which a substance combines with oxygen at a high temperature, releasing light and heat. It is an exothermic and irreversible change. C 1. A change in which the chemical composition of a substance remains the same is called a physical change. No new substance is formed. For example, water freezing into ice; where the ice is water molecules that are bonded together, but it is still water. A physical change is often easy to reverse. For example, the change of ice into water; when water cools, it converts into ice again. Heat or light may or may not be given out or consumed. Physical changes are temporary changes. For example, melting of chocolates, glowing of a bulb, cutting of grass, boiling or freezing of water, making sugar or salt solution in water. 2. A change in which the chemical composition of a substance changes is called a chemical change. A new substance is formed. For example, the burning of wood gives the products ash and carbon dioxide, which were not there when burning started. Most of the chemical changes are irreversible. For example, curdling of milk; curd cannot be turned back into milk. 3. When a substance changes from the solid state to the vapour state without melting, then it is called sublimation. Sublimation of Ammonium Chloride-Sublimation can be used to separate ammonium chloride from other substances. The mixture of ammonium chloride and salt is taken in a china dish. It is covered with a funnel. The tail of the funnel is plugged with cotton wool. The china dish is heated on a tripod stand. Ammonium chloride vaporises and gets deposited near the tail end of the funnel as solid crystals. Salt is left in the china dish. 4. Changes that occur naturally and are not under our control are called natural changes. Natural changes that are desirable are: blooming of owers, formation of clouds, evaporation. 5. Physical changesEvaporation: fast, periodic, reversible man-made, non- Boiling: fast, man-made, non-periodic, reversible Freezing: fast, man-made, non-periodic, reversible Making sugar/salt solution in water: fast, man-made, non-periodic, reversible Chemical changesRusting: slow, irreversible natural, non-periodic, Coagulation of egg: fast, manmade, non periodic, irreversible Cooking of food: fast, manmade, nonperiodic, irreversible Growth of plant: slow, natural, nonperiodic, irreversible Heat or light, or both, are given out or consumed. 6. a. Cooking rice: fast, desirable, manmade, chemical Chemical changes are permanent changes. For example, burning of fuel, digestion of food, ripening of fruits, cooking of foods, formation of compounds such as fertilizers, detergents, etc b. Ripening of fruits: slow, desirable, chemical 19 c. Drying of leaves: slow, physical, d. Day and night: desirable, physical e. Digestion of food: desirable, chemical f. Acid rain: man-made, chemical g. Formation of fog: slow, reversible, physical h. Burstling of reworks: fast, man-made, chemical i. fermentation of dough: slow, desirable, man-made, chemical j. Nitrogen xation: slow, desirable, chemical D 1. Increase in air temperature raises the temperature of water at the evaporation source, which means that more energy is available to the water molecules for converting from the liquid to the gaseous state. Hence, the warmer the evaporating surface, the higher the rate of evaporation. That s why clothes dry faster when the sun shines. 2. Melting of wax is a physical change as only change of state occurs from solid to liquid and is reversible. Whereas the burning of a candle is a chemical change and irreversible. On burning, wax changes into other by-products along with heat and light. 3. Digestion of food is a natural change as once food enters our mouth, saliva starts working and the process of digestion starts. 4. Growing crops is man-made, as the seeds are to be sowed. Once seeds are sown, growth of plant starts, thus the growth of plant becomes a natural change. Some plants make take days and some may take months to grow. 5. Evaporation is a fundamental part of the water cycle and is constantly occurring in nature. It is a slow and reversible change. Water can be obtained by cooling the vapours. It is a desirable change, as it maintains the water cycle. It can be undesirable when there is shortage of water. Also, lower pressure on the open surface of the liquid results in the higher rate of evaporation. 6. Curdling of milk may be undesirable if it leads to the spoilage of milk and desirable if there is a need for curd. E 1. Changes that occur repeatedly after regular intervals of time and whose occurrence can be predicted are called periodic changes. For example, phases of the moon, heartbeat 2. A change that releases energy in the form of heat is called an exothermic change. The reactants have more energy than the products. Energy is released as the products are formed. The container in which an exothermic change is taking place will be warm. For example, rusting of iron 3. Changes that do not repeat themselves at regular intervals of time are called nonperiodic changes. For example, natural phenomenon like earthquakes, cyclones 4. Any change that brings about destruction is an undesirable change. For example, cutting of trees, rusting of iron. 5. Changes that occur due to the action of human beings are called man-made changes. For example, cutting of trees, construction of bridges, roads and dams, etc. 6. A change in which the chemical composition of a substance changes is called a chemical change. A new substance is formed. Most of the chemical changes are irreversible and permanent. For example, curdling of milk; the burning of wood. F 1. Water vapour is formed when water molecules are present in the air, while steam is formed when water is heated to the point that it turns into gas. In simpli ed science, both are referred to as the gaseous state of water. 2. The process in which a substance in the liquid state changes into the gaseous state at any temperature below the boiling point is called evaporation. On the other hand, the process by which a liquid turns into a vapour when it is heated to its boiling point is called boiling. 20 3. The process by which a liquid turns into a vapour when it is heated to its boiling point is called boiling. Whereas condensation is the change of the physical state of matter from the gas phase to the liquid phase and is the reverse of evaporation. b. c. 4. Growth of a tree is a natural and desirable change, whereas cutting of trees is a manmade and undesirable change. 3. a. 5. Melting, or fusion, is a physical process that results in the state transition of a substance from a solid to a liquid. It is a fast, reversible, endothermic and desirable or undesirable change. On the other hand, when a substance changes from the solid state to the vapour state without melting, then it is called sublimation. It is endothermic and desirable change. b. LEARNING ZONE c. Picture based questions 1. a. 1. Cotton plug 2. Inverted funnel 3. Ammonium chloride solidi ed 4. Ammonium chloride vapours 5. China dish 6. Mixture of ammonium chloride and salt b. Ammonium chloride vaporises and gets deposited near the tail end of the funnel as solid crystals. c. There is no visible colour change. d. It is an endothermic change. e. Sublimation can be used to separate materials like ammonium chloride, camphor and iodine from other substances. 2. a. When iron nails are dipped in copper sulphate solution, then after some time a brown layer of copper gets deposited on iron nail. This change is due to chemical reaction between copper sulphate and iron. The colour of copper sulphate solution also changes from blue to green colour due to formation of iron sulphate. Copper sulphate solution (blue) Iron sulphate(green) + Copper(brown) It is a chemical change. Brown layer of copper gets deposited on iron nail. This change is due to chemical reaction between copper sulphate and iron. It is not a desirable change. It is sunset. It is a physical change. The red colour in the sky at sunset is due to an effect called Rayleigh scattering. This means, a large amount of blue and violet light has been scattered so the light that is received by an observer is mostly of a longer wavelength and therefore appears to be red. Movement of the pendulum and the hands of clocks, phases of the moon, motion of the earth. It is a desirable change. Think and answer 1. Our bodies show rise in temperature internally on a hot day, so we sweat, which is cool liquid that cools our skin. When the sweat evaporates, it brings the heat along with the sweat so it cools it even more. That is why its very dangerous when we don t sweat in very hot conditions. We can burn up internally. The rate of sweating is directly related to our body temperature 2. Apples contain an enzyme (called polyphenol oxidase or tyrosinase) that reacts with oxygen and iron-containing phenols that are also found in the apple. The oxidation reaction basically forms a sort of rust on the surface of the fruit. This browning occurs when the fruit is cut or bruised because these actions damage the cells in the fruit, allowing oxygen in the air to react with the enzyme and other chemicals. 3. Brinjal turns brown due to the oxidation of phenolic compounds in the cut surface. Exposure to the atmosphere and the action of oxidative enzymes such as polyphenol oxidase, lead to this reaction in cut surfaces. 21 Immersing in salt solution prevents contact with oxygen to the cut surface, thus delaying the darkening. 4. When turmeric powder comes in contact with lime paste, due to the acidic conditions, turmeric changes its colour from yellow to red. Thus, it is a chemical change. Answers to Worksheets WORKSHEET 1 2. 1. a, b, d, f, g are chemical changes while c, e, h are physical changes. Whole chalk piece 2. Iron gets rusted because of reaction with oxygen present in moist air. In coastal areas, air contains more moisture because of sea or ocean, while in deserts air is dry and hot. Thus, because of getting more moist air, iron objects get rusted faster in coastal areas than in deserts. 3. In burning of wood, new substances are formed, thus it is a chemical change; while in cutting the wood into small pieces, no new substance is formed, thus, it is a physical change. 4. When baking soda is mixed with lemon juice, bubbles are formed due to the evolution of CO2 gas. This is a chemical change because a new substance is formed. WORKSHEET 2 b. Physical c. Evolved Ice Broken chalk piece Water Cold water Paper Hot water Fresh bread Burnt Paper Child Unripe mango Ripe mango Rotten bread 3. We know that ships are made of wood and iron in the same fraction and a part of them remains under water. On the part above water, water drops keep clinging to the ship s outer surface. Moreover, the water of the sea contains many salts. The salt water makes the process of rust formation faster. Therefore ships suffer a lot of damage from rusting inspite of being painted. So, that a fraction of ship s iron has to be replaced every year. 4. 1. a. Calcium Carbonate Baby 1. Burning of candle Chemical Energy is change evolved 2. Lighting of bulb Physical change Energy is evolved 3. Preparation of Chemical Energy is food by green change absorbed plant d. Crystallisation e. Reversible f. Magnesium oxide 22 4. Volcanic eruption Chemical Energy is change evolved 5. Lightening Physical change Energy is evolved 3 Elements, Compounds and Mixtures Learning Objectives Students will be able to: know elements, compounds and their representation understand mixtures and how these are different from compounds learn about different types of mixtures understand separation techniques know about the principles of separation techniques learn the combination of methods for separation Warm-up Start the chapter by interacting with students about the things around them such as a steel glass, lemon juice, a chalk piece, a wooden stick, an iron nail, smoke from a car. Now, ask them which of these are composed of a single substance and which are a combination of two or more. Let them recall the following. Matter Pure substance Mixtures Compounds Homogeneous Elements Heterogeneous atoms and form molecules of that element like nitrogen, sulphur. Make them aware of the fact that an atom itself is made up of even smaller particles called subatomic particlesprotons, neutrons and electrons. To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. Mixtures and its Types Tell the students the difference between mixtures and compounds and different types of mixtures. Solid solid mixture: For example, rice and sand; dal and rice; soil, salt and our Solid liquid mixture: For example, sugar syrup, salt solution, starch solution Concept Explanation Pure Substance Explain to the students that elements are pure substances made of only one kind of atom. Some elements, such as helium, argon exist as single atoms and some cannot exist as single atoms and combine with one or more Liquid liquid mixture: For example, lemon juice, alcohol and water; oil and water; milk and water Gas solid mixture: For example, smoke and dust particles in air Gas liquid mixture: For example, aerated drinks, oxygen dissolved in water 23 Gas gas mixture: For example, air, acid vapours in air, water vapour in air Explain to the students that depending on the appearance, mixtures can be divided into two types: homogeneous mixtures and heterogeneous mixtures. In a homogeneous mixture, the components cannot be di erentiated by colour, shape or size whereas a heterogeneous mixture is a mixture having a non-uniform composition. Explain to them about solution and alloys. A solution is a homogeneous mixture of two or more substances. The components can be separated by evaporation or crystallisation. An alloy is a homogeneous mixture of two or more metals or a metal and a non-metal. Suspension and emulsion are examples of heterogeneous mixture. Suspension is a mixture containing solid particles that can be separated by ltration. For example, sand in water or chalk in water, whereas two immiscible liquids form an emulsion. In most cases, one of the components is water. A mixture of oil and water is an emulsion. To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. Separation Techniques Explain to the students that there is a need for separating mixtures as a part of puri cation. Handpicking, sieving and winnowing are the methods that we use in our daily life and certain separation techniques are used in laboratories. Separating Solid-Solid Mixtures Sublimation is one of the techniques used to separate a solid-solid mixture which involves a change from the solid to the vapour state without melting. A mixture of ammonium chloride and salt is separated by this method. Separating Solid Liquid Mixtures Evaporation, distillation, centrifugation are the techniques which are used to separate the components of a solid-liquid mixture. Evaporation is the process in which a liquid changes into a gas at a temperature below its boiling point. When a salt solution is heated, water evaporates, leaving the salt behind. Distillation is the method of separation of a liquid from a soluble component by rst converting the liquid into its vapour and then condensing the vapour. Distilled water used in laboratories and batteries is obtained using this method. Separating Liquid Liquid Mixtures The components of a liquid liquid mixture can be separated by using a separating funnel or by fractional distillation. In a separating funnel, a liquid mixture when poured into the funnel and allowed to stand, separates into di erent layers. A mixture containing oil and water is separated using this method. Fractional Distillation is used to separate mixtures comprising miscible liquids like alcohol and water and is based on the difference in the boiling points of the liquids. Crude petroleum oil is re ned using this principle. Combinations of Methods for Separation Explain to the students that a mixture which has more than two components can be separated into individual components by a combination of the methods of separation. Explain by taking example of mixture of iron lings, ammonium chloride and sand. Reinforce To reinforce, ask the students to read the Summary and Glossary sections and do the Exercises and Learning Zone sections from the textbook. Help students develop skills (research and thinking) given in the Skills for Life section in the chapter. Explore Ask students to do the Learn by Doing section given at the end of the chapter. 24 Worksheet 1 1. Name the technique to separate: a. Butter from curd _________________ b. Salt from seawater _________________ c. Camphor from salt _________________ 2. De ne the following terms. a. Emulsion ______________________________________________________ _____________________________________________________________________ b. Centrifugation ______________________________________________________ _____________________________________________________________________ c. Distillation ______________________________________________________ _____________________________________________________________________ 3. Give two examples of each. a. Gas solid mixture ______________________________________________ b. Solid liquid mixture ______________________________________________ c. Liquid liquid mixture ______________________________________________ d. Gas gas mixture ______________________________________________ 4. a. Identify the process of separation. b. When is this process used? c. Give an example of the mixture separated by this process. 25 Worksheet 2 1. Look at the gure and answer the following questions. Cotton Inverted funnel Sublimate Perforated asbestos sheet Mixture a. Identify and de ne the process. _____________________________________________________________________ b. Give two examples of mixtures that are separated by this method. _____________________________________________________________________ c. When is this process preferred? _____________________________________________________________________ 2. On what principle is the process of fractional distillation based? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 3. How will you separate a mixture of wheat grains and salt? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 4. What are the factors on which the separation technique depends? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 26 Answers to Coursebook PART I A 1. (b) 2. (d) 3. (c) 4. (c) 5. (c) B 1. any 2. mixture 3. gas-liquid 4. heterogeneous 5. suspension 6. sieving 7. froth oatation C 1. True 2. False 3. True 4. True 5. True 6. False 7. True 8. False D 1. Handpicking 2. Winnowing 3. Sublimation 4. Centrifugation 5. Froth Floatation E 1. Water 2. Colloids 3. Air 4. Distillation 5. Fractional distillation 2. Element - carbon, iodine, Compound - CO2, quick lime, sugar Mixture - milk, vegetable oil, blood, fog, butter 3. An alloy is a homogeneous mixture of two or more metals or a metal and a non-metal. Alloys are obtained by melting the metals together. Brass is an alloy of copper and zinc. 4. Sublimation is a chemical process where a solid turns into a gas without going through a liquid stage. The substance that sublimes separate by this method. This method is also used to purify compounds. For example, a mixture of ammonium chloride and salt can be separated by sublimation as ammonium chloride sublimes. 5. Solid solid mixture: For example, rice and sand PART II A 1. It has a de nite composition and xed chemical properties. A pure substance can be an element or a compound. Solid liquid mixture: For example starch solution Liquid liquid lemon juice 2. Air is a mixture of different gases like CO2, O2, nitrogen etc. 7. Ammonium chloride 8. Centrifuge B 1. a. Sieving b. Separating Funnel c. Centrifugation d. Magnetic separation example, Gas liquid mixture: For example, aerated drinks 4. Rice mixed with stones or pulses containing clay particles can be separated by handpicking. 6. It is used to separate metal ore from impurities in the case of ores lighter than the impurities. For Gas solid mixture: For example, smoke and dust particles in air 3. Sieving, handpicking are the methods of separating a mixture of two solids. 5. It is used to separate the components of a mixture based on the di erence in density. mixture: Gas gas mixture: For example, water vapour in air C 1. There is a stopcock at the tail end of the funnel. It is used to control the ow of the liquid. A liquid mixture, when poured into the funnel and allowed to stand, separates into different layers. Each layer can be drawn out into different containers by opening the stopcock. A mixture of immiscible liquids called emulsions such as oil and water is separated using this method. The separation of emulsions is based on the principle that the lighter liquid will oat above the heavier liquid. 27 2. The principle of froth otation method is the differential wetting of components of a mixture by water. It is used to separate metal ore from mud and other impurities in the case of ores lighter than the gangue or impurities. For example, sulphide ores such as galena (ore of lead) and zinc blende (ore of zinc). The impure ore is mixed in water in a tank, to which pine oil and ethyl xanthate are added. When air is bubbled through the mixture from the bottom of the tank, a thick froth is formed. As sulphide ores are insoluble in water and are lighter, they are carried away by the froth to the surface and are skimmed off. Impurities, as they get wet by the water, become heavy and settle at the bottom. Refer g. 3.7 from the textbook. 3. a. Suspension: A suspension is a heterogeneous mixture containing solid particles that are suffciently large for sedimentation. The components can be separated by ltration. It is a mixture in which the solute particles do not dissolve but get suspended throughout the bulk of the medium. A suspension is formed when particles are left oating around freely in a solvent. Some examples of suspensions are sand in water, chalk in water, dust in air, etc. b. Emulsion: Two immiscible liquids form an emulsion. In most cases, one of the components is water. A mixture of oil and water is an example of emulsion. When one of the components is thicker and present in excess, the emulsion is a semi-solid or paste, for example face creams. c. Alloy: An alloy is a homogeneous mixture of two or more metals or a metal and a non-metal. Alloys are obtained by melting the metals together. Brass is an alloy of copper and zinc. 4. a. Centrifugation: Finely suspended solid components in a liquid are separated by spinning the mixture in a closed container at a very high speed. This 28 is called centrifugation. It is used to separate the components of a mixture based on the difference in density. Centrifugation is used in cases where ltration doesn t work due to the smaller size of the solid particles. For example, colloids like blood, milk b. Fractional distillation: This is used to separate mixtures comprising miscible liquids like alcohol and water. It is based on the difference in the boiling points of the liquids. Crude petroleum oil is re ned using this principle. 5. Unlike salt and sand, iodine sublimes upon heating, so we can heat the mixture and sublime iodine and condense iodine vapors using a sublimation apparatus. Now, we can use water to separate salt and sand. Salt will dissolve in water and with the help of ltration process sand will be left behind. Then evaporate water from salt solution to get salt. 6. The method of the separation of a liquid from a soluble component by rst converting the liquid into its vapour and then condensing the vapour is called distillation. If the liquid component is required in a pure form, the solution is subjected to distillation. The principle behind this separation method is the difference in the boiling points of the components of the mixture. The distillation apparatus comprises a distilling ask which is a round-bottomed ask with a side tube. The side tube is connected to a Liebig condenser and a receiver. A thermometer is inserted into the ask. When heated, the component with the lower boiling point evaporates before the one with the higher boiling point. Vapours get cooled as they pass through the condenser. The condensed liquid collects in the receiver. The solid component remains in the ask. In evaporation, the liquid component of a mixture turns into vapour and is lost to the atmosphere. In distillation, the liquid component can be recovered. D 1. As sulphide ores are insoluble in water and are lighter, they are carried away by the froth to the surface and are skimmed o , that s why froth otation is best suited for the puri cation of sulphide ores. 2. 2. Finely suspended solid components in a liquid are separated by spinning the mixture in a closed container at a very high speed. When a suspension of a solid in liquid is subjected to a spin, the heavier substance will settle at the bottom due to the centrifugal force. Heavier particles experience a larger centrifugation force than the lighter particles. 3. Colloidal solution is a heterogeneous mixture in which particle size of substance is intermediate of true solution and suspension. Just like true solutions, colloidal particles are small enough and cannot be seen through naked eye. They easily pass through lter paper. 4. Fractional distillation is based on the difference in the boiling points of the liquids. The fractionating column is used, as a thermometer is inserted into it. The temperature across the column varies; it is higher at the bottom and lower at the top. The vapours of the component with a higher boiling point condense at the bottom of the column. The liquid with the lower boiling point vaporises rst and rises up. 3. 4. 5. Evaporation is used in place of distillation in preparation of salt, as distillation is expensive because large amounts of energy are needed to heat the seawater increases the use of fossil fuels- which are non-renewable resources carbon dioxide emissions from burning fossil fuels contribute to global warming. E. 1. In a homogeneous mixture, the components cannot be differentiated by colour, shape or size. They are evenly distributed. The mixture appears as one single entity, whereas a heterogeneous mixture is a mixture having a non-uniform 29 5. composition. The composition varies from one region to another, with at least two phases that remain separate from each other, with clearly identi able properties. A suspension is a heterogeneous mixture containing solid particles that are suf ciently large for sedimentation. The components can be separated by ltration. It is a mixture in which the solute particles do not dissolve but get suspended throughout the bulk of the medium. Particles of the suspension are visible to the naked eye, whereas two immiscible liquids form an emulsion. In most cases, one of the components is water. When one of the components is thicker and present in excess, the emulsion is a semi-solid or paste-like mass. A pure substance has a de nite composition and xed chemical properties. It can be an element or a compound. A pure substance has a xed melting point, boiling point and density. In a mixture, the components are present in any proportion. The components retain their properties. A mixture does not have a speci c boiling and melting point or a characteristic colour, smell or taste. Elements are pure chemical substances that have one or one type of atom. Compounds are chemical substances that are formed from one or more elements, held together by chemical bonds. An element is already in its rawest form and cannot be further broken down. A compound can be broken down into individual elements using chemical reactions. Most compounds form naturally in order to reach stability, as not all elements in the periodic table are stable. Distillation is a process used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have suf cient difference in their boiling points, whereas fractional distillation is a process used to separate a mixture of two or more miscible liquids for which the boiling points of chemicals in a mixture are close to each other. The apparatus for fractional distillation is very similar to that for simple distillation, except that a fractionating column is tted in between the distillation ask and the condenser. LEARNING ZONE Picture based questions 1. a. Centrifuge b. It is found in hospitals, pathology labs, dairy farms and industries. c. It is used to separate the components of a mixture based on the difference in density. Finely suspended solid components in a liquid are separated by spinning the mixture in a closed container at a very high speed. When a suspension of a solid in liquid is subjected to a spin, the heavier substance will settle at the bottom due to the centrifugal force. Heavier particles experience a larger centrifugation force than the lighter particles. d. The mixture is taken in one test tube and water in the test tube just opposite it for proper balancing, This is called the balancing test tube. e. The heavier substance settles at the bottom due to the centrifugal force. Heavier particles experience a larger centrifugation force than the lighter particles. 2. a. 1. Thermometer 2. Fractionating column 3. Water out 4. Condenser 5. Round bottomed ask 6. Water in 7. Bunsen burner 8. Distillate b. Fractionating column is connected to the condenser and there is a thermometer inserted into the fractionating column as it is based on the difference in the boiling points of the liquids. c. Distillate collected is pure. d. The vapours of the other liquid coming along in small quantities will be 3. a. b. c. d. e. condensed and sent back into the ask by the fractionating column. The vapours of the liquid with the low boiling point rise and are condensed in the condenser. This liquid is then collected in a container. Froth Floatation 1. Feed 2. Bubbles 3. Heavy gangue 4. Froth 5. Concentrate launder Mostly sulphide ores, as these are insoluble in water and are lighter. They are carried away by the froth to the surface and are skimmed off. The principle of this method is the differential wetting of components of a mixture by water. It is used to separate metal ore from mud and other impurities in the case of ores lighter than the gangue or impurities. Sulphide ores such as galena (ore of lead) and zinc blende (ore of zinc). Think and answer 1. Froth oatation is used in the case of ores lighter than the gangue or impurities. As sulphide ores are insoluble in water and are lighter, they are carried away by the froth to the surface and are skimmed off. Impurities, as they get wet by the water, become heavy and settle at the bottom. This would not have been possible over belt of magnetic separation. In other cases, magnetic separation is used. 2. To separate the mixture of kerosene, water, sand and salt ,we have to use combination of methods. The mixture of kerosene oil and water is poured in a separating funnel. It is kept undisturbed till two separate layers of oil and water are visible. Open the stopcock of the separating funnel and pour the lower layer into a beaker carefully. Close the stopcock immediately as the other layer reaches near the stopcock. Kerosene is left in the separating funnel and water is obtained in the beaker. Salt is dissolved in water and with the help of ltration process sand will be left behind. 30 Then evaporate water from salt solution to get salt. So on dissolving the mixture of sugar and salt in alcohol, the sugar would dissolve but salt remains undissolved. The undissolved salt will settle at the bottom and can simply be separated by ltration. Now the solution of sugar and alcohol can simply be evaporated over a water bath and the sugar can thus be separated from the alcohol solution. 3. Water cannot be used to separate a mixture of sugar and salt as both salt and sugar show good solubility in water. Salt being an ionic compound would not be soluble in alcohol. On the other hand, sugar is soluble in alcohol. Answers to Worksheets WORKSHEET 1 c. Rice mixed with stones or pulses containing clay particles can be separated by handpicking. 1. a. Centrifugation b. Evaporation WORKSHEET 2 c. Sublimation 2. a. Two immiscible liquids form an emulsion. In most cases, one of the components is water. A mixture of oil and water is an emulsion. b. Finely suspended solid components in a liquid are separated by spinning the mixture in a closed container at a very high speed. This is called centrifugation. It is used to separate the components of a mixture based on the difference in density. c. The method of the separation of a liquid from a soluble component by rst converting the liquid into its vapour and then condensing the vapour is called distillation. 3. a. smoke and dust particles in air 1. a. Sublimation. Sublimation is the phase transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase. b. Mixture of ammonium chloride and salt can be separated by sublimation as ammonium chloride sublimes, napthalene and iodine can be separated from their mixtures. c. The substance that sublimes separate by this method. This method is also used to purify compounds. 2. This is used to separate mixtures comprising miscible liquids like alcohol and water. It is based on the difference in the boiling points of the liquids. 3. Sieving b. sugar syrup, starch solution 4. The separation technique used depends upon the properties of its components such as: c. alcohol and water; oil and water d. air, water vapour in air 4. a. Handpicking Physical state b. If the components can be di erentiated by colour, size and shape and one of the components is less in quantity, the mixture can be separated by handpicking. 31 Size, shape and colour Boiling point, melting point, density, volatility, solubility, magnetic properties, ability to sublime, etc. 4 Atomic Structure Learning Objectives Students will be able to: know about the fundamental subatomic particles understand the structure of an atom learn about the discovery of electrons, protons and neutrons understand various atomic models to study structure of the atom learn different isotopes and isobars understand the electronic con guration of various elements know about ionic and covalent bonds Warm-up Start the chapter by interacting with the students regarding matter and what it is made up of? According to their previous knowledge, they would answer an atom, is not divisible. Give them various examples where matter is broken into ne pieces like chalk, clay, a piece of , etc. Tell them that even the smallest visible pieces also contain even smaller particles. Now, let the students answer the question given in the Warm-up section. Concept Explanation Fundamental subatomic particles and Dalton s atomic theory Explain to the students the Dalton s Atomic Theory which states that matter is made of indivisible particles called atoms and that atoms can neither be created nor destroyed. But later discoveries and studies concluded that atoms are divisible and are composed of subatomic particles known as electrons, protons and neutrons. Discovery of Electrons Explain to the students about the discovery of electrons, protons and neutrons. Thomson discovered rays (known as cathode rays) which were composed of negatively charged particles known as corpuscles and were later known as electrons. Later, Goldstein discovered positive rays which were found to be composed of positively charged particles and were named as protons. Let the students know that later neutrons were discovered which were electrically neutral having mass equal to the protons. Later Rutherford discovered the positive centre of the atom known as nucleus which consists of protons and neutrons. To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. 32 Thomson s Atomic Model Electronic Con guration Explain to the students the Thomson s Atomic Model according to which an atom is considered a watermelon fruit, which has a positively charged body and seeds are the electrons. Also tell them about Rutherford s Atomic Model according to which nucleus is in the centre and electrons revolve round it in circular orbits similar to planets around the sun. This model could not explain the properties of the atom as spinning electron, while orbiting the nucleus, will lose energy and fall into the nucleus and as a result, the atom will collapse. Explain to the students the electronic con guration of various elements with the help of rules followed by lling of energy levels. Make them understand that maximum number of electrons which an energy level can hold is 2n2 where n=1, 2, 3, 4 = K, L; M, N....... and the electron will rst enter the lowest energy level available. Rutherford s Model and Bohr s Atomic Model Formation of Molecules Explain to the students that Rutherford s model was modi ed by Niels Bohr, who proposed a 3D model in which electrons revolve around the nucleus in different circular paths called shells/orbits. Each shell has a de nite amount of energy and electrons also acquire the energy of the shell. Electrons tend to occupy the lowest energy level available. Subatomic Particles Explain to the students about the subatomic particles. The number of protons or the number of electrons forms the atomic number whereas the total number of protons and neutrons in the nucleus forms the mass number. Octet Rule Explain to the student the octet rule, i.e., stability of atoms with 8 electrons in their outermost shell. Let students understand that an atom is an unstable particle and to gain stability it forms molecules. Explain to the students the different types of chemical bonds. Ionic bond is formed by gaining or losing electrons in order to complete the octet. Metals complete the octet by losing electrons while non-metals complete the octet by gaining electrons. Let students understand that when electron transfer is not easy, sharing of electrons is done and the bond formed between the atoms is called covalent bond. Reinforce To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. To reinforce, ask the students to read the Summary and Glossary sections and do the Exercises and Learning Zone sections from the textbook. Help students develop skills (research and thinking) given in the Skills for Life section in the chapter. Isotopes and Isobars Explore Make students aware of the terms isotopes (atoms of the element with same atomic number and different mass numbers) and isobars (two different elements with same mass number). Ask students to do the Learn by Doing section given at the end of the chapter. 33 Worksheet 1 1. Name the following. a. Three subatomic particles _________________ b. Smallest particle of matter that cannot be divided further _________________ c. The positive centre of the atom _________________ d. Circular paths around the nucleus on which electrons revolve _________________ e. Two different elements which have the same atomic mass _________________ f. Element with atomic number 1 _________________ 2. Complete the following table. Shell Name of the shell n=1 K Maximum number of electrons 2x2x2=8 M 2x 4 x 4 = 32 3. Why do atoms combine? ________________________________________________________________________ ________________________________________________________________________ 4. The atomic number of boron is 5. Write its electronic con guration. ________________________________________________________________________ ________________________________________________________________________ 5. What is ground level? ________________________________________________________________________ ________________________________________________________________________ 34 Worksheet 2 1. Compare ionic and covalent bonds on the basis of their solubility and melting and boiling points. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 2. If an atom contains one proton and one electron, will it carry any charge or not? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 3. Helium atom has an atomic mass of 4 u and 2 protons in its nucleus. How many neutrons does it have? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 4. Complete the following table. Atomic Number 9 Mass Number ___ Number of Neutrons 10 Number of Protons ___ 16 32 ___ ___ ___ 24 ___ 12 ___ 2 ___ 1 35 Answers to Coursebook PART I A 1. (b) 2. (c) 3. (a) 4. (b) 5. (a) 6. (d) B 1. neutrons 2. ionic 3. same 4. hydrogen 5. orbitals C 1. False 2. False 3. True 4. True 5. False 6. True D 1. Nucleus 2. CaO 3. Barium 4. Mass number 5. Hydrogen E 1. Neutron 2. Shells 3. y-rays 4. Covalent bond 5. Ethyl alcohol 6. Nucleons F 1. (d) 2. (c) 3. (e) 4. (b) 5. (a) They cast shadows of objects kept in their path. They cause mechanical motion in a paddle wheel kept in their path. 2. a. 2, 6 b. 2, 8, 8, 1 c. 2, 8, 7 d. 2, 8, 4 3. Refer gure 4.17 from the textbook. 4. PART II A 1. It is the number of protons (positively charged) in an atom. As the number of electrons is equal to the number of protons, atomic number is also equal to the number of electrons in the atom. 2. 2, 8, 18, 2 3. Valency of X is 4 and Y is 2. 4. It is the combining capacity of an element. It is the number of electrons gained or lost by an atom during a chemical reaction. 5. Same element with atoms having the same atomic number but different mass numbers are called isotopes. Isotopes of hydrogen are: 1H1, 1H2, 1H3. H1: Protium, one electron and one proton. 1 H2 : Deuterium, one electron, one proton 1 and one neutron. H3 : Tritium, one electron, one proton and 1 two neutrons. B They originate from the cathode and move towards the anode. They are composed of negatively charged particles. They are de ected by electric and magnetic elds. S No Ionic bond Covalent bond 1 They are water They exist as soluble solids. solids, liquids, and gases. Some of these compounds are water soluble. 2 They are good They are nonelectrolytes, as electrolytes they are polar in nature. 3 They have They have low high melting melting and points boiling points 5. Atoms which have 8 electrons in their outermost shell are stable. They do not react with other elements. This is known as the octet rule. For example, inert gases, helium, neon, argon, krypton and xenon are called inert gases or noble gases. They are also called rare gases. For example, helium: 2, neon: 2, 8, argon: 2, 8, 8 C 1. The main postulates of Dalton s atomic theory are: 36 Matter is made up of tiny indivisible particles called atoms. Atoms are the smallest particles of matter and cannot be divided further. Atoms of the same elements are alike but atoms of di erent elements are di erent. The number and type of atoms in a given compound are always xed. Atoms can neither be created nor destroyed. Atoms combine in whole number ratios to form compounds. For example, in CO2 and CO, the ratio of the number of carbon atoms to oxygen atom is 1 : 2 and 1 : 1, respectively. Properties of compounds are different from those of the constituent elements. 2. In Rutherford s alpha scattering experiment, a very thin gold foil was bombarded by -particles. The following observations were recorded. Most of the -particles passed through the foil and their path was unchanged. This shows that most of the space in the atom is empty. A few particles deviated but passed through the foil. This shows that a positively charged body is present at the centre of the atom. Very few particles were repelled and they bounced back. This shows that the positively charged centre is very small and hard, and the mass of the atom is concentrated at the centre. Conclusions: From the gold foil experiment, Rutherford called this positive centre the nucleus of the atom and concluded that it consists of protons and neutrons. Refer g.4.7 and 4.8, page 53 3. Niels Bohr modi ed Rutherford s atomic model in order to explain the stability of the atom. He proposed a 3D model, instead of Rutherford s planar model. Its main features are as follows. Electrons revolve around the nucleus in di erent circular paths called shells. These shells are also called orbitals . Each shell is associated with a de nite amount of energy which is constant. 37 Electrons do not have energy of their own but acquire the energy of the shell they occupy. Hence, the shells are also called energy levels. Electrons tend to occupy the lowest energy level available. This level is also called the ground level. When an electron is excited, it can jump to higher energy levels. When an electron moves back to its ground state, the extra energy is emitted as radiation. The shells are numbered 1, 2, 3 and so on, starting from the rst shell around the nucleus. They are named as K, L, M, N, O and so on. The maximum number of electrons each shell can hold is denoted as 2n2, where n is the serial number of the shell. n = 1 is the K shell. It is the lowest energy level. It can accommodate 2 electrons. Refer g. 4.10 and 4.12 from the textbook. 4. In the year 1879, he discovered a stream of particles which were till now unknown. Thomson was conducting an experiment in a discharge tube. A discharge tube is a long glass tube which is fused at both ends and tted with two electrodes. It was connected to the terminals of a high voltage source. The air in the tube was gradually removed to reduce the pressure. When the pressure was 0.001 atmospheres and the voltage was 10000 V, a stream of particles emerged from the cathode and travelled towards the anode. They were detected by a uorescent glow around the anode. Since they emerged from the cathode, Thomson called them cathode rays. Thomson studied the properties of cathode rays. He placed the tube between a positively charged plate and a negatively charged plate and discovered that the rays de ected towards the positive plate. He concluded that these rays are negatively charged particles. Observations: neutrons in the nucleus. Therefore, atoms of the same element can have the same atomic number but different mass number. The difference is due to a different number of neutrons. Cathode rays cast shadows of objects kept in their path. This shows that cathode rays travel in a straight line. Cathode rays could make a paddle wheel kept in their path, rotate. This shows that cathode rays consist of a stream of fast moving particles. The particles which composed the cathode rays were named electrons. The name electron was given by the Irish physicist, George Johnstone Stoney. 2. Atoms are mostly unstable. They become stable when they combine to form molecules. Atoms with 8 electrons in the outermost shell are stable, so other atoms also attain stability by completing their octet. 3. Ionic compounds are formed by sharing or losing of electrons. Metals have 1, 2 or 3 electrons in their valence shell. By giving them away, they have 8 electrons in the penultimate shell and they complete the octet. Non-metals like chlorine, oxygen and nitrogen accept 1, 2 and 3 electrons, respectively, to complete their octet. Both attain stability by the transfer of electrons. But in a case where number of electrons is more than three in the valence shell, transfer of electrons is not easy and nucleus won t be able to handle 4 or more electrons, so the elements chooses to share its electrons to complete its octet and hence follows octet rule. The study of electrons led to the discovery of the following facts about electrons. They are negatively charged. An electron has a charge of nearly 1.06 10 19 coulombs. The mass of an electron is approximately 1/1837 of a hydrogen atom. 5. a. Na (11) 2, 8, 1 b. P (15) 2, 8, 5 c. S (16) 2, 8, 6 d. Ar (18) 2, 8, 8 e. Zn 2, 8, 18, 2 4. Inert gases have 8 electrons in their outermost shell and are stable. They do not react with other elements, and hence known as noble gases. f. Kr 2, 8, 18, 8 6. Frederick and Irene Curie discovered that when a sheet of Beryllium was bombarded by -particles, a stream of particles emerged. When these particles were passed through paraffn wax, these produced -particles. James Chadwick studied the rays emerging from the beryllium sheet and found that they had a mass equal to that of the protons, but no charge. They were electrically neutral. He called these particles neutrons . E 1. Atoms of the same element with same atomic number but different mass numbers are called isotopes. The difference is due to a different number of neutrons. C12, C13 and C14 are isotopes of carbon. On the other hand, two different elements which have the same atomic mass are called isobars. For example, argon and calcium. Refer g. 4.6 from textbook D. 1. Atomic number is the number of protons in an atom. As the number of electrons is equal to the number of protons, atomic number is also equal to the number of electrons in the atom, whereas mass number is the total number of protons and 38 2. It is the number of protons (positively charged) in an atom. As the number of electrons is equal to the number of protons, atomic number is also equal to the number of electrons in the atom. Atomic number Z = Number of protons = Number of electrons On the other hand, Mass Number or 5. Valency is the combining capacity of an element. The valency of metals is usually the number of electrons present in the outermost shell. The valency of a nonmetal is given by the formula: 8 minus the number of electrons in the outermost shell. It may also be de ned as the magnitude of charge carried by an ion. Atomic Mass is the total number of protons and neutrons in the nucleus. Atomic mass or mass number = Number of nucleons = Number of protons + Number of neutrons Number of neutrons = Mass number (A) Atomic number (Z). 3. The bond formed by the transfer of electrons i.e.by gaining or losing of electrons to attain stability is called ionic bond. The ions formed are held together by a strong electrostatic force, which is called the ionic bond. While covalent bond is formed by sharing of electrons to attain stability. LEARNING ZONE Picture based questions 1. a. Sodium atom b. Atomic number -11 Mass number -23 c. The valence shell M has 1 electron. Hence, the sodium atom has to lose its 1 valence electron to become stable and its valency is 1. 4. Metals have 1, 2, 3 electrons in their outermost shell and they tend to lose electrons and non-metals gain electrons to complete the noble gas con guration. 5. Electrons are negatively charged particles. An electron has a charge of nearly 1.06 10 19 coulombs and the mass of an electron is approximately 1/1837 of a hydrogen atom. Protons are positively charged particles. Their charge equals 1.06 10 19 coulombs and the mass of each proton is equal to a hydrogen atom. On the other hand, neutrons have no charge. They are electrically neutral and have mass equal to that of the protons. d. Since sodium loses its 1 valence electron to become stable, it forms cation Na+. 2. C12, C13 and C14 are isotopes of carbon. C12: number of electrons = 6, number of protons = 6, number of neutrons = 6, C13: number of electrons = 6, number of protons = 6, number of neutrons = 7 C14: number of electrons = 6, number of protons = 6, number of neutrons = 8 3. a. carbon and oxygen atoms b. carbon = 4 and oxygen = 2 c. CO2 F 1. -rays are emitted during radioactivity. They are heavier, positively charged and can penetrate through most solids. d. NaCl e. Both sodium and chloride have valency one. 2. The positive centre of the atom is called nucleus and it consists of protons and neutrons. The mass of the atom is concentrated at the centre. 3. The protons and neutrons found in the nucleus are called as nucleons. 4. Mass Number or Atomic mass is the total number of protons and neutrons in the nucleus. Atomic mass or mass number = Number of nucleons = Number of protons + Number of neutrons f. Ionic bond is present in sodium chloride. g. It is an ionic compound. Think and answer 1. The Bohr s model of the atom is generally taught in the classrooms due to its simplicity. But this model is not suitable considering that electrons are wave-like clouds moving at fractions of light speed in a state of probability following the rules of quantum mechanics, and not as tiny dots surrounding a nucleus. 39 Bohr s model has been replaced by Quantum Model of the Atom (which shows electron clouds ) single positively charged proton and a single negatively charged electron bound to the nucleus by the Coulomb force. It tries not to achieve octet but doublet. Also there is no electron-electron repulsions. In everyday life on Earth, isolated hydrogen atoms (called atomic hydrogen ) are extremely rare. Instead, hydrogen tends to combine with other atoms in compounds, or with itself to form ordinary (diatomic) hydrogen gas, H2. 2. Hydrogen does not belong to any family of elements, and though it is a non-metal, it appears on the left side of the periodic table with the metals. Difference between hydrogen atom and any other atom is that it is electrically neutral atom, contains a Answers to Worksheets WORKSHEET 1 5. Electrons tend to occupy the lowest energy level available. This level is called the ground level. 1. a. Electron, proton, neutron b. Atoms WORKSHEET 2 c. Nucleus 1. Ionic compounds are water soluble solids. They have high melting points whereas covalent compounds exist as solids, liquids, and gases and some of these compounds are water soluble. They have low melting and boiling points. d. Orbits / Shells e. Isobars f. Hydrogen 2. Maximum number of electrons Shell Name of the shell n=1 K 2 1 1=2 n=2 L 2 2 2=8 n=3 M 2 3 3 = 18 n=4 N 2 4 4 = 32 2. An electron is a negatively charged particle whereas a proton is a positively charged particle. The magnitude of their charges is equal. Therefore, an atom containing one electron and one proton will not carry any charge. 3. Atoms with 8 electrons in the outermost shell are stable. Other atoms also want to attain stability by completing their octet. This can be done either by transferring electrons from one atom to another, or sharing electrons between two atoms, so that both complete their octet. This gives rise to bonding (force of attraction) between the two atoms. 4. Boron B Atomic number-5 Electronic con guration-2, 3 40 3. Number of neutrons = Mass number (A) Atomic number (Z) Number of neutrons= 4 2 = 2. 4. Atomic Mass Number of Number of Number Number Neutrons Protons 9 19 10 9 16 32 16 16 12 24 12 12 1 2 1 1 5 Language of Chemistry Learning Objectives Students will be able to: know the symbols of elements understand the formulae of compounds learn about the valency of elements and ions represent compounds by chemical formulae learn about chemical equations and their balancing understand the application of Law of Conservation of Mass know the limitations of chemical equations understand the information gathered from a chemical equation Warm-up Formulae of Compounds Start the chapter by revising the symbols of various elements and their valencies. Give them simple examples of writing the formula of compounds like sodium chloride and water. Explain to the students the representation of chemical formula. Make them aware of the fact that the valency of an element is equal to the number of electrons present in the outermost shell of the atom of an element. Ca and Mg have 2 valence electons in their outermost shell and are divalent. Valency of ions is indicated by the loss or gain of electrons by an atom. Now let students complete the exercise given in the Warm-up section Concept Explanation Symbols of Elements Explain to the students that chemical symbols or abbreviation is used to represent an element. Generally, the rst letter of the name of an element is used but if two or more elements have their names beginning with the same letter, one more letter is added to the symbol. Give students the example of chromium (Cr) and chlorine (Cl). Symbols of some elements are derived from their Latin names like gold (Au). Its Latin name is Aurum. To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. Representation of Compounds Explain to the students the steps involved in writing the chemical formula of a compound. Start by writing symbols side by side. Mention the valency below each symbol. Now interchange the valencies and write as subscripts and write the ratio of valencies in the lowest terms. 41 of reactants and products. Chemical Equations Explain to the students that when chemical reaction is represented using symbols and formulae, it is called a chemical equation. The substances that take part in a reaction are reactants and the substances formed are called products. Make students understand that a chemical equation is based on the law of conservation of mass and an equation can be balanced by making the atoms of various elements equal on both sides. Balancing Chemical Equations Explain them by giving example of the equation: Fe +HCl FeCl2 + H2 In this equation, Fe is balanced but hydrogen and chlorine are not balanced. To balance hydrogen and chlorine on both sides, multiply HCl by 2, which makes the equation as: Fe +2HCl FeCl2 + H2 Now, give various examples to the students to balance the equations. To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. Applying The Law of Conservation of Mass Explain to the students the balancing of chemical equation by applying the law of conservation of mass on the atomic masses Information Gathered from a Chemical Equation Let students know that a chemical equation gives a lot of information like symbols and formulae of reactants and products, number of atoms and molecules in the reactants and in the products formed, the ratio of number of molecules of reactants and products and also their masses. But besides all this information, it has limitations also. It gives no information on the physical status of the reactants and products, nature of the reaction, and the time taken for the completion of the reaction. Limitations of Chemical Equations Explain to the students that a chemical reaction is in uenced by many factors like surface area, pressure, catalyst, temperature and heat, light, electricity, physical status. Reinforce To reinforce, ask the students to read the Summary and Glossary sections and do the Exercises and Learning Zone sections from the textbook. Help students develop skills (research and thinking) given in the Skills for Life section in the chapter. Explore Ask students to do the Learn by Doing section given at the end of the chapter. 42 Worksheet 1 1. Write the formula of the following compounds. a. Magnesium chloride _________________ b. Calcium carbonate _________________ c. Nitric acid _________________ d. Carbon monoxide _________________ e. Potassium carbonate _________________ 2. An element A has valency Y and an element B has valency X. If both the elements combine, what is the formula of the resultant compound? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 3. Write the balanced equations for the following. a. Hcl + NaOH NaCl + H2O _______________________________________ b. Na + H2O NaOH + H2 _______________________________________ c. Fe + H2O Fe3O4 + H2 _______________________________________ d. Pb(NO3)2 PbO + NO2 + O2 _______________________________________ 4. What are reversible reactions? Give one example. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 5. Differentiate between exothermic and endothermic reactions. Give one example of each. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 43 Worksheet 2 1. State the difference between positive and negative catalysts. ________________________________________________________________________ ________________________________________________________________________ 2. When will the reaction be faster? a. Solid reactant is in a powder form or b. In the form of lumps Explain why. ________________________________________________________________________ ________________________________________________________________________ 3. The formula of the chloride of a metal is MCl2. What will be the formula of its sulphate? Explain. ________________________________________________________________________ ________________________________________________________________________ 4. Write the names of compounds represented by the following formula. Also show the ions present in them. a. Al2 (SO4)3 ____________________ b. KNO3 ____________________ c. CaCO3 ____________________ d. CaCl2 ____________________ 5. Complete the following table: Name Formula Ammonia SO2 Carbon disulphide 44 Elements present Answers to Coursebook PART I A 1. (c) 2. (a) 3. (c) 4. (d) 5. (a) B 1. Balancing 2. equal to 3. photochemical 4. catalyst 5. precipitate C 1. True 2. True 3. True 4. True 5. False 6. True 7. True 8. False D 1. Element-Carbon 2. Sulphide ion 3. Sodium Chloride 4. Barium ion 5. Silver Chloride E 1. Jones Jacob Berzelius 2. Cobalt 3. Valence electrons 4. Cation 5. Products F. 1. N2 +3H2 2NH3 2. 2H2 +O2 2H2O 3. Na2O +H2O 2NaOH 4. 2CO +O2 2CO2 5. Zn + 2HCl ZnCl2 + H2 2. 1 C 4 3 O 2 2. AlCl3 Aluminium chloride, Na2CO3 Sodium carbonate 3. a. CaCl2 b. NH3 c. NaNO3 4. Balanced equation is the equation in which the number of atoms of elements on both sides of a chemical equation are equal. 5. Zn(s) + 2HCl(aq) ZnCl2(aq) +H2(g) B 1. A chemical equation gives the following information. It gives the symbols of elements and the formulae of compound as reactants and products. It tells us the names of substances taking part in a reaction, called reactants, and the substances formed, called products. It gives the number of atoms and molecules in the reactants taking part in the reaction and in the products formed. It gives the ratio of the number of molecules of reactants and products. PART II A 1. Element Valency Na Al It gives the ratio of the masses of reactants and the products formed. Electronic Con guration Symbol Atomic Number Atomic Mass Valency 2,8,1 Na 11 23 1 2,8,7 Cl 17 35.5 1 2,4 C 6 12 4 45 3. The balanced equation is ii. Write the valencies below each 2Mg + O2 2MgO +1 2 iii. Interchange the valencies and Na (CO 3)1 write as subscripts Mass of Mg= 24 2= 48 iv. Ratio of valencies in the lowest terms Mass of MgO=2 (24 + 16) = 80 Applying the unitary method, 48 g of Mg forms 80 g of MgO Therefore, 24g Mg will form = (80 24)/48 g =40 gm of MgO v. Chemical formula of carbon dioxide 2:1 Na2CO3 2. a. N2+H2 NH3 4. Chemical formula represent a compound showing symbols of elements along with the valencies. i. First, write unbalanced equation for the given reaction. 5. Photosynthesis is the photochemical reaction. ii. Examine the number of atoms of each element present in the unbalanced equation. example of sunlight 6CO2 + 6H2O C6H12O6 +O2 iii. To balance hydrogen on left hand side, put coef cient 3 as 3H2 . C 1. a. Carbon dioxide i. Write the symbols side by side C O ii. Write the valencies below each +4 2 iii. Interchange the valencies and write as subscripts C2 O4 iv. Ratio of valencies in the lowest terms 1:2 v. Chemical formula of carbon dioxide CO2 N2 + 3H2 NH3 iv. To balance hydrogen atoms on right hand side, put coef cient 2 as 2NH3 . N2 + 3H2 2NH3 v. Now consider the element nitrogen. Nitrogen atoms are 2, on both, left and right hand side. b. Calcium oxide i. Write the symbols side by side Ca O ii. Write the valencies below each +2 2 iii. Interchange the valencies and write as subscripts Ca2 O2 iv. Ratio of valencies in the lowest terms 1:1 v. Chemical formula of carbon dioxide CaO vi. Thus, balanced chemical equation is: N2 + 3H2 2NH3 b. STEP 1. Examine the number of atoms of different elements present in the unbalanced equation: Na + Cl2 NaCl c. Ferric oxide i. Write the symbols side by side ii. Write the valencies below each iii. Interchange the valencies and write as subscripts Fe STEP 2. Pick an element to balance the equation. In the above equation, Na is balanced and chlorine is not balanced . O 3 2 Fe2 O3 iv. Ratio of valencies in the lowest terms 2:3 v. Chemical formula of carbon dioxide Fe2O3 STEP 3. To balance chlorine on both sides, we need to multiply NaCl by 2, which makes sodium atoms equal to 2 on the reactant side. i. Na + Cl2 2NaCl ii. 2Na + Cl2 2NaCl d. Sodium carbonate i. Write the symbols side by side N2 + H2 NH3 iii. Now, sodium has 2 atoms on both sides Na CO3 46 The balanced equation becomes: 2Na +Cl2 2NaCl 5. A chemical equation can be made more informative by including the following- c. CaCO3+HCl CaCl2 +H2O +CO2 The physical status of the reactants and products, i.e., whether they are solids, liquids or gases. STEP 1. Examine the number of atoms of different elements present in the above unbalanced equation The concentration products. STEP 2. Ca is balanced, C is balanced, hydrogen and chlorine needs to be balanced. reactants and The time taken for the completion of the reaction. Multiply Cl of HCl by 2, which balances hydrogen also. The rate at which a reaction proceeds. The heat changes during the reaction, i.e., whether the heat is given out or absorbed. Three atoms of oxygen on reactant side equals three atoms of oxygen on product side. The conditions such as temperature, pressure, catalyst, etc. which affect the reaction. Thus, the balanced equation becomes: CaCO3 + 2HCl CaCl2 +H2O +CO2 3. Catalysts are chemical substances that increase or decrease the speed of a reaction. Catalyst does not take part in the chemical reaction. of The nature of the reaction, i.e., whether it is reversible or irreversible. D 1. 4Na + O2 2Na2O Catalysts are speci c in nature, which means we cannot use the same catalyst in all the reactions. For example, potassium chlorate decomposes in the presence of manganese dioxide. 2KClO3 MnO 2KCl + 3O2 2 a. Atomic mass of Na 4 x 23 = 92 Atomic mass of sodium oxide = 124 Ratio of the masses of sodium and sodium oxide is Na : Na2O = 92:124 23:31 Iron is used as a catalyst in the preparation of ammonia. 4. A chemical equation should be balanced as according to the atomic theory, the number of atoms of elements on both sides of a chemical equation should be equal. They only transfer and share electrons among themselves in forming newer compounds. A balanced chemical equation gives the number of atoms and molecules in the reactants taking part in the reaction and in the products formed. It gives the ratio of the number of molecules of reactants and products. It also gives the ratio of the masses of reactants and the products formed. 47 b. 92 g of Na forms 124 g of Na2O 124 1g of Na will form = 92 Therefore 9.6g of Na will form 9.6 124 = 92 = 12.9 g air 2Fe2O3 2. a. 4Fe + 3O2 water b. Atomic mass of Fe is 56 Mass of Fe = 4 56 = 224 Mass of Fe2O3 = 2(112 + 48) = 320 Ratio of the masses of Iron and iron oxide = Fe : Fe2O3 224 : 320 = 7:10 of 244 g of KClO3 c. 224g of Fe when oxidised forms 320 g of Fe2O3 320 1g of Fe will form = 224 320 11.2 11.2 g of Fe will form = 224 =16 g 224 1 g will be formed by 96 g 9.6 g of oxygen is formed by decomposition of 9.6 244 = 24.4g of potassium chlorate 96 6. S + O2 d. For producing 320g of Fe2O3, 224g of Fe was required Mass of S = 32 To produce 32 g of Fe2O3, Fe required is 224 32 = 22.4g = 320 3. a. S(s) + O2(g) SO2(g) Mass of oxygen = 2 16 = 32 Mass of SO2 = 32 + 32 = 64 32 g of S is required to burn 32 g of oxygen Therefore, 40 g of S is required to burn 40 32 g of oxygen = 32 = 40 g b. Mass of S = 32 Mass of oxygen = 2 16 = 32 Masses of S : SO2 = 32 : 64 = 1 : 2 c. i. Mass of S reacted = 96g 35g = 61 gm ii. 32 g of S produces 64 g of SO2 64 1 g of S will produce 32 g of SO2 61 g of S will produce 64 61 = 122g of SO2 32 4. 2Mg + O2 2MgO Mass of Mg = 2 24 = 48 Mass of oxygen = 2 16 = 32 E 1. There is no mass change during chemical reaction as it follows atomic theory and the law of conservation of mass. According to the atomic theory, the number of atoms of elements on both sides of a chemical equation should be equal. They only transfer and share electrons among themselves in forming newer compounds. According to law of conservation of mass, matter is neither created nor destroyed. A chemical equation can be balanced by applying this law on the atomic masses of reactants and products. Mass of Magnesium oxide = 2(24 + 16) = 80 When 48 g of Mg is burnt, 80 g of MgO is formed 80 1 g of Mg forms = 48 g 80 120 g of MgO 120 g of Mg forms = 48 = 200 g 5. 2KClO3 2KCl + 3O2 Mass of Potassium Chlorate = 2(39 + 35 + 48) = 244 Mass of oxygen = 96 96 g of oxygen is formed by decomposition 48 2. Metals have 1, 2, 3 electrons in their outermost shell and they easily lose electron(s) to form a positive ion called a cation, to complete the octate and attain stability. 3. When two or more elements have their names beginning with the same letter, one more letter is added to the symbol in order to avoid confusion. For example, chromium has the symbol Cr and chlorine has the symbol Cl. Thus, some symbols have two letters. 4. Helium belongs to a group of inert gases. These are also known as noble gases as they have full outer shells and are stable. They need not react with other elements to attain stability. F 1. A symbol is an abbreviation used to represent an element, whereas the number of atoms of elements present in one molecule of a compound which are represented using the chemical symbols of its constituent elements, is called a formula. Generally, the rst letter of the name of an element can be used as a symbol like oxygen is represented as O. H2O, which means one molecule of water, contains 2 atoms of hydrogen and 1 atom of oxygen. 2. An atom or a group of atoms that loses electron(s) forms a positive ion and is called a cation. For e.g. Sodium ion Na+. An atom or a group of atoms that gains electron(s) forms a negative ion and is called an anion. For example, Oxygen (Oxide ion) O2 . 3. Chemical reaction is the reaction when 2 or more substances react and a new substance is formed. Colour change, odour formed, gas given off, precipitate formed, energy change can easily be described, while a biochemical change is a chemical change that usually refers to a chemical change that occurs within a plant or animal. Often these require enzymes. Oxygen O Sulphur S Helium He Sodium Na Silver Ag Hydrogen H Nitrogen N Phosphorus P Boron B Bromine Br Calcium Ca Gold Au b. Sodium and nitrogen c. Carbon and calcium d. Silver and gold e. Jones Jacob Berzelius, a Swedish chemist. 2. a. XP d. YP3 3. 4. A chemical reaction in which heat is given out is called an exothermic reaction. For example, C + O2 CO2 + Heat A reaction in which heat is absorbed from the surroundings is called the endothermic reaction. b. X2Z c. Y2Z3 e. YQ3 Ion Chemical Formula Compound Calcium Ca2+ CaCl2 Sulphur S2 H 2S Phosphate PO4 (NH4)3PO4 Carbonate CO32 CaCO3 Ammonium NH4+ NH4Cl Chloride Cl NaCl Magnesium Mg 3 MgO 2+ Polyatomic ions are = phosphate, carbonate, ammonium For example, 2C + O2 + Heat 2CO LEARNING ZONE Think and answer Picture based questions 1. a. chloride Cl 1 b. oxide O2 2 1. a. Element Symbol Carbon C c. nitride N3 I d. sulphate SO4 Iodine 49 3 2 2 Answers to Assessment 1 A. 1. (a) 2. (b) 3. (a) 4. (b) 5. (c) B. 1. The space between the particles of matter either atoms or molecules is called interparticle space. 2. A process by which a substance changes from the liquid state to the gaseous state at any temperature below its boiling point is called evaporation. 3. A substance that is dissolved in another substance (solvent), forming a solution is called a solute. For e.g. in a sugar solution, sugar is a solvent. 4. Froth otation is the method of separation of a mixture based on the principle of differential wetting. It is used to purify sulphide ores. 5. Covalent bond is the bond formed by sharing of electrons to complete the octate and attain stability. C. 1. (e) 2. (a) 3. (d) 4. (c) 5. (b) D. 1. Valency 2. Chemical equation 3. Covalent bond 4. Electronic con guration 5. Valence electrons E. 1. Atomic number is the number of protons in an atom. As number of protons is equal to the electrons, atomic number is also equal to the number of electrons in the atom. On the other hand, atomic mass is the number of protons and neutrons in the nucleus. 2. Physical change Chemical change a. A change in which the chemical composition of a substance remains the same. A change in which the chemical composition of a substance changes. b. No new substance is formed A new substance is formed. c. Changes are temporary Changes are permanent F. 1. True 2. False 3. False 4. False 5. True G. 1. Changes that take place slowly are called slow changes. For examples, germination of seeds, rusting of iron, etc. 2. Condensation is the change of the physical state of matter from the gas phase to the liquid phase and is the reverse of evaporation. 3. Camphor and Iodine 4. The process by which a liquid changes into a soft, semi-solid mass is called curdling. For example, curdling in milk. When lime juice is added to milk, it changes into cottage cheese. 5. Digestion is a natural change as the process automatically starts once the food enters our mouth. It is the process by which food is broken down into simple chemical compounds that can be absorbed and used as nutrients and undigested part is eliminated from the body as waste. 6. Two immiscible liquids form an emulsion. In most cases, one of the components is water. A mixture of oil and water is an emulsion. 50 7. Finely suspended solid components in a liquid are separated by spinning the mixture in a closed container at a very high speed. This is called centrifugation. It is used to separate the components of a mixture based on the difference in density. H. 1. According to law of conservation of mass, matter is neither created nor destroyed. A chemical equation can be balanced by applying this law on the atomic masses of reactants and products. If a reactant or a product is a compound, then the atomic mass of each constituent element must be used to calculate the molecular mass of the compound. For example, in the equation: Fe + HCl FeCl2 + H2 the atomic mass of Fe = 55.85u; H = 1u; Cl = 35.5 Therefore, the molecular mass (average mass of a molecule) of reactants and products becomes Fe + HCl FeCl2 + H2 55.85 (1+35.5) 55.85+ (1 2) (35.5 2) 55.85 36.5 126.85 2 Total mass (of reactants) on LHS = 55.85 + 36.5 = 92.35 Total mass (of products) on RHS = 126.85 + 2 = 128.85 Difference of mass = 128.85 92.35 = 36.5 = Mass of one molecule of HCl, which should be added to the LHS. Therefore, the balanced equation is: Fe + 2HCl FeCl2 + H2 55.85 2(1+35.5) 55.85 + (1 2) (35.5 2) 55.85 73 126.85 2 Total mass (of reactants) on LHS = 55.85 + 73 = 128.85 Total mass (of products) on RHS = 126.85 + 2 = 128.85 2. Fermentation is a chemical change as it is the chemical breakdown of a substance by bacteria, yeasts or other microorganisms, typically involving the release of carbon dioxide (in the form of bubbles) and heat. It is a chemical change brought about by enzymes. 51 3. The purpose of separating the components of a mixture is to: a. remove unwanted and harmful substances. b. Obtain pure and useful substances. For e.g. Sieving- This method of separating a mixture involves using a sieve. If particles differ in size, they can be separated by sieving. The larger particles remain on the sieve while the smaller particles pass through. 4. The main points of Rutherford s atomic model are described below. a. An atom consists of a positively charged nucleus, which is surrounded by electrons moving around it. b. The nucleus of an atom consists of protons and neutrons because the whole mass of the atom is concentrated in the nucleus. c. The electrons are distributed in the empty space of the atom around the nucleus in different, concentric, circular paths, called orbits. d. The number of electrons in orbits are equal to the number of positive charges (protons) in the nucleus. Hence, the atom is electrically neutral. e. The volume of the nucleus is very small as compared to the volume of the atom. f. Most of the space of the atom is empty. 5. Atoms always want to attain stability by completing their octate. This can be done either by transferring electrons from one atom to another or by sharing electrons between two atoms, so that both complete their octate. This gives rise to bond (force of attraction) between the two atoms and is known as chemical bond. There are two common types of bonds. Electrovalent Bond or Ionic Bond- Metals have 1, 2 or 3 electrons in their valence shell. By giving them away, they have 8 electrons in the penultimate shell and they complete the octate. Non-metals like chlorine, oxygen and nitrogen accept 1, 2 and 3 electrons, respectively, to complete their octate. Both attain stability by the transfer of electrons. Metals become cations (positively charged ions) and nonmetals become anions (negatively charged ions). The oppositely charged ions are held together by a strong electrostatic force, which is called the ionic bond. For e.g. sodium chloride Covalent Bond- When the number of extra or de cient electrons is more than 3, transfer of electrons is not easy. In such cases, atoms of two elements share their electrons between them and form a covalent bond. For e.g. Carbon dioxide molecule. I. 1. a. Hydrogen b. Lithium c. Sodium atom d. Potassium 2. one 3. H=1 Li=3 Na=11 K=19 Answers to Worksheets WORKSHEET 1 reaction. 1. a. MgCl2 c. HNO3 e. K2CO3 2. A y b. CaCO3 d. CO For example, 2C + O2 + Heat 2CO N2 + O2 + Heat 2NO B These same reactions can be written as 2C + O2 2CO Heat x N2 + O2 2NO Heat Formula = AxBy WORKSHEET 2 3. a. Hcl + NaOH NaCl + H2O b. 2Na + 2H2O 2NaOH + H2 c. 3Fe + 4H2O Fe3O4 + 4H2 heat 2PbO + 4NO + O d. 2Pb(NO3)2 2 2 4. Reversible reactions proceed in the forward and backward directions. It means as soon as the product is formed, it decomposes to give the reactants. H2 + I2 2HI 5. A chemical reaction in which heat is given out is called an exothermic reaction. 1. A positive catalyst is used to increase the speed of a reaction whereas a negative catalyst is used to decrease the speed of a reaction. An example of a reaction with a negative catalyst is the decomposition of H2O2 in the presence of phosphoric acid (works as a negative catalyst) as well as the oxidation of chloroform in the presence of alcohol (works as a negative catalyst). So, the name of the catalyst must be mentioned in the chemical reaction. Phosphoric acid H2O2 H2 + O2 2. Instead of lumps, if the solid reactant is in a powder form, the reaction will be faster. For example, C + O2 CO2 + Heat N2 + 3H2 2NH3 + Heat A reaction in which heat is absorbed from the surroundings is called the endothermic 52 The reason for this is that a large surface area for contact facilitates the reaction. 3. Valency of Cl is 1. Since one atom of M has 2Cl atoms attached to it, so the valency of M is 2. CaCl2 is calcium chloride M SO4 +2 2 Ions Ca2+ and Cl MSO4. Thus the formula of sulphate of metal M will be MSO4. 4. Al2(SO4)3 is aluminium sulphate Ions Al3+ and SO42 KNO3 is potassium nitrate Ions K+ and NO3 CaCO3 is calcium carbonate Ions Ca 2+ and CO3 2 53 Formula Elements present Ammonia NH3 N and H Sulphur dioxide SO2 S and O Carbon disulphide CS2 C and S Carbon tetrachloride CCl4 C and Cl 5. Name Model Test Paper 1 Time: 3 hours Total marks: 50 Section A A. Fill in the blanks. [5] 1. The _______________ is applied in balancing a chemical equation. 2. In the process of photosynthesis, chlorophyll acts as a _______________ . 3. Chemical equation gives the ratio of the masses of _______________ and _______________ . 4. The process of separating the constituents of a mixture into useful materials is called _______________ . 5. According to the kinetic theory of matter, particles of matter are in constant _______________ and they _______________ with each other. B. Multiple choice questions. [5] 1. The collisions between molecules of gases are a. Elastic b. Inelastic c. Dependent on the molecules d. No collision occurs between molecules. 2. Melting of chocolate is a. Physical change b. Chemical change c. Periodic change d. Irreversible change 3. Sublimation of naphthalene balls is a/an a. irreversible, endothermic and desirable change. b. reversible, exothermic and desirable change. c. reversible, endothermic and desirable change. d. irreversible, exothermic and desirable change. 4. Centrifugation is used to separate the components of a mixture based on the a. difference in their arrangement b. difference in density c. difference in mass d. difference in size 5. Valency is equal to the number of a. electrons and neutrons b. protons and neutrons c. neutrons d. electrons in the outermost shell of the atom of an element C. State True or False. [5] 1. An element with a valency of 1 is said to be monovalent. 2. Chemical formula of Zinc Sulphate is Zn(SO4)2 3. Winnowing separates a mixture by using wind or blowing air 4. On heating, the particles of solid start to vibrate faster 5. A stream of particles emerging from anode and travelling towards cathode are called cathode rays. 54 D. Name the following. [4] 1. The electrode connected to the positive terminal of an electric current source 2. Representation of a chemical reaction using symbols and formula 3. A process by which a substance changes from the gaseous state to the liquid state on cooling 4. A homogeneous mixture of two or more metals or a metal and non-metal. Section B A. De ne the following. [3] 1. Suspension 2. Electronic con guration 3. Catalyst C. Short answer questions. [12] 1. Differentiate between the following. a. Reactants and Products b. Freezing and condensation 2. Explain how painting of iron gate prevents it from rusting 3. List the steps to write the formula of calcium hydroxide C. Long answer questions. [12] 1. Explain the process to separate a mixture of immiscible liquids. 2. What is an electrovalent bond? Explain the formation of NaCl along with its diagrammatic representation. 3. Look at the picture carefully and answer the following questions a. Name the atomic model. b. How are electrons lled in various energy levels? c. What happens when an electron moves from higher to its ground state? d. What is the maximum number of electrons each shell can hold? 4. On heating, calcium carbonate (CaCO3) decomposes to give calcium oxide (CaO) and carbon dioxide (CO2) a. Calculate the mass of calcium oxide produced when 150 g of calcium carbonate is heated b. How much calcium carbonate is required to produce 168 g of calcium oxide. 55 6 Chemical Reactions Learning Objectives Students will be able to: understand chemical reactions and their characteristics know about the different types of chemical reactions learn about direct combination, decomposition, single displacement and double displacement learn the reactivity series predict the reactivity of metals learn neutralisation reaction, endothermic and exothermic reaction, oxidation and reduction reaction understand the decomposition reactions to form oxides and various types of oxides Warm-up be same on both sides. Start the chapter by interacting with students regarding various symbols, formulae and compounds. Let them recollect the formulae of various compounds and their reaction with some metals. Also ask them regarding the position of metals and non-metals in the periodic table. Characteristics of a Chemical Reaction Now let students complete the exercise given in the Warm-up section. Explain to the students various characteristics of a chemical reaction like evolution of gas, heat 2KCl + 3O 2KClO3 2 a. Evolution of gas in the form of bubbles e.g. Zn + H2SO4 ZnSO4 + H2 hydrogen Concept Explanation Activity: To observe the evolution of a gas during a chemical reaction Chemical Reaction Materials required: A glass, baking soda and vinegar Explain to the students that in a chemical reaction, existing bonds are broken and new bonds are formed with the evolution or absorption of energy. Elements that take part in a chemical reaction are called reactants and which are formed are called products. The number of atoms of each element should Procedure: Take a pinch of baking soda in a glass. Add a small amount of vinegar in it. Brisk effervescence is obtained when vinegar is added to baking soda. Thus, in this chemical reaction, carbon dioxide is obtained in the form of effervescence. 56 b. Change in colour e.g. Blue copper sulphate crystals when heated become white. b. Decomposition reaction: A compound breaks up into elements or simpler compounds on heating. CaCO3 CaO + CO2(g) c. Odour Lime stone For e.g. c. Single displacement reaction: (substitution reaction) FeS + 2HCl FeCl2 + H2S Hydrogen sulphide A more reactive element displaces a less reactive element from a compound and takes its place. (smell of rotten eggs) d. Formation of precipitate AgNO3 + NaCl AgCl + Na NO3 FeSO4 + Mg MgSO4 + Fe (White ppt) Activity: To observe precipitation in a chemical reaction Materials required: Test tube, ferrous sulphate solution and sodium hydroxide solution Procedure: Take 2 mL of ferrous sulphate solution in a test tube. Add a few drops of sodium hydroxide solution to the test tube. Reaction: FeSO4(aq) + 2NaOH(aq) Fe(OH) + Na2SO4(aq) dirty green ppt A thick dirty green precipitate is formed. Thus, the chemical reaction between ferrous sulphate and sodium hydroxide solutions involves precipitation. e. Change of heat Reaction can be exothermic or endothermic C + O2 CO2 + heat N2 + O2 2NO heat Types of chemical reactions Explain to the students the different types of chemical reactions. a. Direct combination or synthesis: Two or more elements or compounds combine to form a new product. H2(g) + Cl2(g) 2HCl Quick lime d. Double displacement reaction: Two compounds exchange their ions. AgNO3 + NaCl AgCl + NaNO3 (ppt) One of the products is always a precipitate. Reactivity series Explain to the students the reactivity series in which metals are arranged in decreasing order of their reactivity. Metals above hydrogen in the series can displace hydrogen from dilute acids, while metals below hydrogen cannot displace it from dilute acids. e. Neutralisation reaction - Acid solution reacts with a base to form salt and water. It is double displacement reaction. 2NaOH + H2SO4 Na2SO4 + 2H2O To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. f. Exothermic and endothermic reactions: Heat given out in a reaction Exothermic reaction C + O2 CO2 + heat Heat absorbed from the surrounding Endothermic reaction. 2C + O2 2CO heat g. Oxidation and reduction: Oxidation involves either addition of oxygen, removal 57 of hydrogen or loss of electrons from an atom or ion. a. Acidic oxides Non-metal + Oxygen acidic oxide S + O2 SO2 (also known as acid anhydrides) 2HI + Cl2 2HCl + I2 (Covalent in nature) 2Na + Cl2 2NaCl Reduction involves removal of oxygen, addition of hydrogen or any other electropositive element or gain of electrons from an atom or an ion. 2CuO 2Cu + O2 SO3 + H2O H2SO4 b. Basic oxide Metal + Oxygen basic oxide (ionic in nature) Na2O + H2O 2NaOH c. Amphoteric oxide H2 + Cl2 2HCl CuO + H2 Cu + H2O Let students understand that when oxidation and reduction occur simultaneously, reaction is known as redox reactions. Show both acidic characteristics. as well as basic Oxide + acid Salt + Water (Basic property) Oxide + alkali Salt + Water FeO3 + 3CO 2Fe + 3CO2 (Acidic property) Fe2O3 is reduced and CO is oxidised. Decomposition reactions to form oxides d. Neutral oxide Explain to the students the formation of oxides by calcination and roasting. In calcinations, metal ores (from which metal is extracted) are heated in the absence of air or in a limited supply of air to form oxide, whereas in roasting, ore is heated in a regular supply of air in a furnace called reverberatory furnace at a temperature below the melting point of the metal. Some oxides neither show acidic nor basic characteristics Types of oxides Explain to the students the four types of oxides Eg. Oxides of NO and CO. Reinforce To reinforce, ask the students to read the Summary and Glossary sections and do the Exercises and Learning Zone sections from the textbook. Help students develop skills (research and thinking) given in the Skills for Life section in the chapter. 58 Worksheet 1 1. Name the following. a. A solid residue, which is one of the products of the reaction _______________ b. Process of addition of electrons to form anions _______________ c. Compounds of oxygen with other elements _______________ d. Oxides which do not exhibit acidic or basic characteristics _______________ e. Gas evolved when vinegar is added to baking soda _______________ 2. Write the balanced chemical equation for the following. Indicate the gas formed. a. Reaction of sodium with hydrochloric acid _____________________________________________________________________ b. Reaction of calcium carbonate with hydrochloric acid. _____________________________________________________________________ c. When potassium chlorate is heated. _____________________________________________________________________ 3. a. What happens when barium chloride solution is mixed with sodium sulphate solution. _____________________________________________________________________ _____________________________________________________________________ b. Write the balanced chemical equation. _____________________________________________________________________ _____________________________________________________________________ c. What is the white substance formed known as? _____________________________________________________________________ _____________________________________________________________________ 59 Worksheet 2 1. What happens when a. Carbon burns in oxygen _____________________________________________________________________ b. Quick line is mixed with water. _____________________________________________________________________ c. Silver nitrate reacts with sodium. _____________________________________________________________________ 2. What is the reactivity series of metals? Name the most reactive metal and the least reactive metal of the series. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 3. Differentiate between acidic and basic oxides on the basis of following points. a. Reaction of oxygen with ________________________________________________________________________ b. Bonds formed in the compounds. ________________________________________________________________________ c. Melting and boiling points. ________________________________________________________________________ 4. Complete the following: Oxidation is: The addition of _______________ or any non-metal. The _______________ of hydrogen or any _______________. The removal of electrons to form _______________ Reduction is: _______________ of hydrogen or any metal atom. The removal of _______________ or any _______________. The _______________ of electrons to form anions. 60 Answers to Coursebook PART I A 1. (a) 2. (b) 3. (b) and (d) both 4. (d) 5. (c) B 1. Symbols or formulae 2. Upward 3. White 4. Hydrogen sulphide 5. Exothermic 6. Combination C 1. True 2. False 3. True 4. False 5. False 6. False 7. True 2. S 3.NaOH D 1. H2O2 4. Redox 5. Oxidation E 1. NO 2. Amphoteric Oxide 3. Redox Reaction 4. Hydrogen peroxide 5. Neutralisation reaction 6. K Potassium 7. Au Gold 8. Lead sulphide (PbS) 5. When a solution of silver nitrate is added to a solution of sodium chloride, a white insoluble substance (precipitate), silver chloride, is formed. AgNO3 + NaCl(aq) AgCl + NaNO3 (aq) ppt (aq) 6. When carbon burns in the presence of oxygen, it releases a large amount of heat. C Carbon + O2 Oxygen CO2 + Heat Carbon dioxide 7. Zinc, Iron and Nickel B. 1. A chemical reaction may be accompanied by one or many of the following characteristics. a. Evolution of Gas: heated strongly 2KClO3 2KCl + 3O2 b. Change in Colour: heat CuO(s) + CO (g) CuCO3(s) 2 c. Odour : S + O2 SO2 pungent smell d. Formation of Precipitate: BaCl2 + Na2SO4 BaSO4 + 2NaCl PART II A 1. A chemical reaction is also called a chemical change. During a chemical reaction, existing bonds are broken and new bonds are formed. Energy is released or absorbed during this process. 2. A double displacement reaction between an acid and a base in which both lose their properties and produce a neutral salt solution in water. 3. FeCl3 + 3NaOH Fe(OH)3 + 3NaCl 4. a. Decomposition reaction. heat CuO(s) + CO (g) b. CuCO3(s) 2 Copper oxide (black solid)) e. Change of State: 2H2(g) + O2(g) 2H2O(l) f. Change of Heat: C + O2 CO2 + Heat 2. When two or more elements or compounds chemically combine to form a new product, it is called a synthesis or combination reaction. On heating, carbon combines with oxygen to form carbon dioxide. It is a combination reaction. The reaction is accompanied by the release of heat and light. (Double displacement reaction) Copper carbonate (green solid) white ppt C + O2 CO2(g) + Heat Carbon dioxide 61 3. High temperature, catalyst initiated, reduction, decomposition reaction 4. H2S + Cl2 2HCl + S It involves removal of hydrogen, so it is an oxidation reaction. 5. Zn + Cl2 Zinc Chlorine ZnCl2 Zinc chloride Here, Zn is oxidised as chlorine is added to it and chlorine is reduced as metal zinc is added to it. The ionic equation becomes Zn Zn+2 + 2e (Oxidation) Cl2 + 2e 2Cl (Reduction) Zn+2 + 2Cl ZnCl2 6. Acidic oxides CO2, SO2, NO2 Basic oxides Na2O, CuO, FeO Amphoteric oxides PbO Direct combination or synthesis: When two or more elements or compounds chemically combine to form a new product, it is called a synthesis or combination reaction. Carbon dioxide On heating, calcium carbonate (limestone) decomposes into calcium oxide (quick lime) and carbon dioxide. Limestone CaO Quick lime + For example, barium chloride reacts with sulphuric acid to form barium sulphate and hydrochloric acid. + Magnesium O2 Oxygen 2MgO Magnesium oxide Removal of Hydrogen H 2S Hydrogen sulphide + Cl2 Chlorine chloride 2HCl + Hydrogen S Sulphur Loss of Electrons CO2(g) + Heat Decomposition : On heating, a compound breaks up into elements or simpler compounds. This is called the decomposition of the substance and such reactions are called decomposition reactions. heat CaCO3 Double displacement: A reaction in which two compounds exchange their ions is called double displacement. 2Mg C. 1. There are four basic types of reactions: Oxygen (aq) CopperIron sulphate Addition of Oxygen Neutral oxides NO, CO Carbon (aq) IronCopper sulphate 2. Oxidation Reaction: During a chemical reaction, when oxygen is added or hydrogen is removed from a substance or there is a loss of electrons from an ion or atom, that reaction is called an oxidation reaction. O2 Fe(s) + CuSO4 Cu(s) + FeSO4 BaCl2 + H2SO4 BaSO4 + 2HCl C + For example, iron is more reactive than copper. Hence, iron displaces copper from copper sulphate solution. When sodium metal reacts with chlorine gas to form sodium chloride (NaCl), the sodium metal loses an electron, which is then gained by chlorine. 2Na + Sodium Cl Chlorine 2NaCl Sodium chloride Na e Na+ (Loss of electrons is oxidation) Cl + e Cl (Gain of electrons is reduction) CO2(g) Carbon dioxide Single displacement: It is a reaction in which a more reactive element displaces a less reactive element from a compound and takes its place. This is also called a substitution reaction. 62 When it loses the electron, means the sodium metal has been oxidised to the sodium cation. Any element or compound which helps in the addition of oxygen or an electronegative element or the removal of hydrogen or an electropositive element is called an oxidising agent An oxidising agent brings about an oxidation reaction. In the above reaction, sodium is oxidised example, MgO Oxides can be classi ed into four types: acidic oxide, basic oxide, amphoteric oxide and neutral oxide. Reduction Reaction : A chemical reaction in which hydrogen or any other electropositive elements like metals are added or oxygen is removed or a gain of electrons from an atom or an ion takes place is called a reduction reaction. Acidic Oxide Non-metals react with oxygen to form acidic compounds of oxides which are held together by covalent bonds. Acidic oxides form acids when they react with water. Addition of Hydrogen Basic Oxide Metals react with oxygen to give basic compounds of oxygen. These compounds are usually ionic in nature. H2 + Cl2 Hydrogen Chlorine 2HCl Hydrogen chloride In this reaction, hydrogen is added to chlorine. So, it gets reduced. CO Carbon monoxide + 2H2 Hydrogen Methanol Removal of Oxygen Copper oxide 2Cu + Copper Basic oxides form bases when they react with water. Na2O + H2O 2NaOH CH3OH In this reaction, hydrogen is added to carbon monoxide. So, it gets reduced. 2CuO SO3 + H2O H2SO4 Amphoteric oxides - are compounds of oxygen which exhibit both acidic as well as basic characteristics. Example: aluminium oxide. Acidic characteristics: O2 Al2O3 + 6HCl 2AlCl3 +3H2O Oxygen In this reaction, oxygen is removed from copper oxide. Hence, copper is reduced. Fe2O3 + 3CO 2Fe + 3CO2 In this reaction, oxygen is removed from iron oxide. Hence, iron is reduced. Gain of Electrons CuO + H2 Cu + H2O In the reaction, copper ion gains two electrons and forms a copper atom. Cu2+ + 2e Cu (Gain of electrons is reduction) Any substance that removes oxygen or electronegative elements from compounds or adds hydrogen or electropositive elements is a reducing agent. In the given reaction, copper oxide is reduced with the help of hydrogen. So, hydrogen is the reducing agent in the given reaction. Hydrogen and carbon are reducing agents. 3. A compound in which oxygen is present as an union is called an oxide. For 63 Basic characteristics: Al2O3 + 2NaOH 2NaAlO2 + H2O Neutral Oxide Some compounds react with oxygen to form oxides, which do not exhibit acidic or basic characteristics. Such compounds are called neutral compounds of oxygen. Examples of neutral oxides are NO and CO. 4. a. Reactions in which the product formed may not be soluble in water. It settles as a precipitate in the test tube are called precipitation reaction. For example, when barium chloride solution is mixed with sodium sulphate solution, a white precipitate is obtained. It is barium sulphate, which is insoluble in water. BaCl2 + Na2SO4 BaSO4 + 2NaCl b. When an acid solution reacts with a base by exchanging their radicals, such that a salt and water are the only products, then the reaction is called a neutralisation reaction. It is a type of double displacement reaction. For example, sulphuric acid (dilute) reacts with sodium hydroxide solution to form sodium sulphate (salt) and water. 2NaOH + H2SO4(dil) Na2SO4 + 2H2O D 1. When oxides of Al react with acid, they undergo a neutralisation reaction to form water and salt. This exhibits the basic property of the compounds. Similarly, these oxides react with alkali to form salt and water, exhibiting the acidic property Acidic characteristics: c. The evolution of gas in the form of bubbles is called e ervescence. For example, when sodium reacts with acids, hydrogen gas is evolved. Al2O3 + 6HCl 2AlCl3 + 3H2O Basic characteristics: Al2O3 + 2NaOH 2NaAlO2 + H2O 2Na + 2HCl 2NaCl + H2 Sodium Hydrochloric Acid Sodium chloride 2. Cu is less reactive than Fe and so cannot displace Fe and so no colour change occurs. hydrogen 5. A list in which different metals are arranged in decreasing order of their reactivity to oxygen, water, mineral acid, etc. is called the reactivity series of metals. 3. Metals have a tendency to donate electrons and get oxidised. Thus, they are reducing agents. 4. Ionic bonding can result from a redox reaction when atoms of an element (usually metal), whose ionisation energy is low, give some of their electrons to achieve a stable electron con guration. In doing so, cations are formed. The activity series of metals help in deciding which metal can displace other metals. Only a more reactive metal can displace a less reactive metal. The reactivity decreases from top to bottom. Metals that occur above hydrogen in the activity series can displace hydrogen from dilute acids. But metals below hydrogen in the reactivity series cannot displace it from dilute acids. The atom of another element (usually nonmetal), whose electron af nity is positive, then accepts the electron(s), again to attain a stable electron con guration, and after accepting electron(s) the atom becomes an anion. a. i. Ag and Cu are present below hydrogen and thus cannot displace other metal. ii. Fe and Zn are present above the hydrogen ,so can displace other metal. iii. Cu is present below hydrogen and is not reactive. So it is not possible. b. K Na Ca Zn 5. Hydrogen is not a metal, but it is included in the metal reactivity series as like metals, hydrogen also forms H+ ions. E. 1. Non-metals react with oxygen to form acidic compounds of oxides which are held together by covalent bonds. These compounds are also called acid anhydrides. Acid anhydrides usually have low melting and boiling points. Acidic oxides form acids when they react with water. Whereas metals react with oxygen to give basic compounds of oxygen. These compounds are usually ionic in nature. They have high boiling and melting points. Basic oxides form bases when they react with water. H Cu Hg Ag 64 2. During a chemical reaction, when oxygen is added or hydrogen is removed from a substance or there is a loss of electrons from an ion or atom, that reaction is called an oxidation reaction. On the other hand, a chemical reaction in which hydrogen or any other electropositive elements like metals are added or oxygen is removed or a gain of electrons from an atom or an ion takes place is called a reduction reaction. 3. Any element or compound which helps in the addition of oxygen or an electronegative element or the removal of hydrogen or an electropositive element is called an oxidising agent. An oxidising agent brings about an oxidation reaction. On the other hand, any substance that removes oxygen or electronegative elements from compounds or adds hydrogen or electropositive elements is a reducing agent. 4. A chemical reaction in which heat is given out is called an exothermic reaction. For example, C + O2 CO2 + Heat, whereas a reaction in which heat is absorbed from the surroundings is called an endothermic reaction .e.g. b. In the reaction, copper ion gains two electrons and forms a copper atom. Cu2+ + 2e Cu, so reduced and H2 is oxidised c. H2S (oxidised) + SO2 (reduced) 3S + 2H2O d. The silver ion, Ag+, is reduced to silver metal, and zinc metal is oxidized to Zn2+ e. 2Al (oxidised) + 6HCl (reduced). 2AlCl3 + 3H2 LEARNING ZONE Picture based questions 1. a. Formation of Precipitate b. Evolution of gas in the form of bubbles c. Green solid changes into a black solid. Also, a colourless, odourless gas is evolved. Heating of copper carbonate(green solid) gives copper oxide (black in colour) and carbon dioxide. 2. a. possible b. not possible c. not possible d. possible e. possible 2C + O2 2CO Heat When the energy absorbed for breaking a bond is more than the energy released during the formation of a new bond, the extra energy will be given out and the surroundings will get heated. On the other hand, if the energy absorbed is less than the energy released during the formation of a bond, the system needs more energy and energy is absorbed. 5. In roasting, the ore is heated in a regular supply of air in a furnace called reverberatory furnace at a temperature below the melting point of the metal whereas metal ores are heated strongly in the absence of air or in a limited supply of air to obtain the oxide by removing carbon dioxide and water is called calcination. F. a. In this reaction, hydrogen atom in H2 are oxidised and Cl in Cl2 are reduced. f. not possible 3. a. Reverberatory furnace b. Roasting c. During roasting, the sulphide is converted to an oxide, and sulphur is released as sulphur dioxide, a gas. heat 2Fe O + 4SO 4FeS + 7O2 2 3 2 d. This process is generally applied to sulphide ores such as zinc blende (ZnS) and galena (PbS). Think and answer 1. The primary difference between metals is the ease with which they undergo chemical reactions. The elements toward the bottom left corner of the periodic table are the metals that are the most active in the sense of being the most reactive. Lithium, sodium, and potassium all react with water, for example. 65 IA and IIA of the periodic table. Metals in the second class are slightly less active. They don t react with water at room temperature, but they react rapidly with acids. The rate of this reaction increases as we go down this column, however, because these elements become more active as they become more metallic. The third class contains metals such as chromium, iron, tin, and lead, which react only with strong acids. It also contains even less active metals such as copper, which only dissolves when treated with acids that can oxidize the metal. Metals in the fourth class are so unreactive they are essentially inert at room temperature. These metals are ideal for making jewellery or coins because they do not react with the vast majority of the substances with which they come into daily contact. As a result, they are often called the coinage metals. Classifying Metals Based on Activity The metals are often divided into four classes on the basis of their activity, as shown in the table below. Thus we can say that in metals reactivity increases as you go down a group because the farther down a group of metals you go, the easier it is for electrons to be given or taken away, resulting in higher reactivity. Common Metals Divided into Classes on the Basis of Their Activity Class I Metals: The Active Metals Across a Period: In metals reactivity decreases as you go across a Period because though they still want to give away valence electrons they have more of them to get rid of, which requires more energy. Li, Na, K, Rb, Cs (Group IA) Ca, Sr, Ba (Group IIA) Class II Metals: The Less Active Metals Mg, Al, Zn, Mn Class III Metals: The Structural Metals Cr, Fe, Sn, Pb, Cu Class IV Metals: The Coinage Metals Ag, Au, Pt, Hg The most active metals are so reactive that they readily combine with the O2 and H2O vapor in the atmosphere and are therefore stored under an inert liquid, such as mineral oil. These metals are found exclusively in Groups 2. The solution of dilute HNO3, ZnCl2 and H2O can be kept in the container made of copper. Since copper is a less reactive metal and is placed below the hydrogen in activity series. Hence it does not react with HNO3, ZnCl2 and H2O. While aluminium is highly reactive metal and can reacts with these solutions. Thus container made of copper is suitable to keep the given solutions. Answers to Worksheets WORKSHEET 1 d. Neutral Oxide 1. a. Precipitate e. CO2 b. Reduction 2. a. 2Na + 2HCl 2NaCl + H2 b. CaCO3 + 2HCl CaCl2 + H2O + CO2 c. Oxides 66 c. 2KCLO3 2KCl + 3O2 decreasing order of their reactivity to oxygen, water, acid etc is called the reactivity series of metals. 3. a. When barium chloride solution is mixed with sodium sulphate solution, barium sulphate and soldium chloride is formed. The most reaction metal is at the top of the series, which is potassium and the least reactive metals at the bottom, which is gold. strongly heated Potassium chlorate Potassium Oxygen Chloride b. BaCl2 + Na2SO4 BaSO4 + 2NaCl Acidic oxide 3. white Ppt. c. Barium sulphate ppt. 4. Heating of copper carbonate (green solid) gives copper oxide (black solid) along with the evolution of colourless, odorless, gas, CO2. WORKSHEET 2 1. a. Carbon burns in oxygen to form carbon dioxide and heat is produced. C + O2 CO2 + heat Basic oxide 1. Reaction of oxygen with Non Metals Metals 2. Bonds formed Covalent bond Ionic bond 3. Melting and boiling point Low melting and boiling point High melting and boiling point 4. Oxidation is: b. When quick lime is mixed with water, calcium hydroxide is formed and heat is produced. CaO + H2O Ca(OH)2 + heat The addition of oxygen or any non-metal The removal of hydrogen or any metal The removal of electrons to form cations Reduction is: c. Silver Chloride and sodium nitrate is formed. AgNO3 + NaCl AgCl + NaNO3 2. A list in which different metals are arranged in 67 Addition of hydrogen or any metal atom The removal of oxygen or any non metal The addition of electrons to form anions 7 Hydrogen Learning Objectives Students will be able to: learn about the rst element in the periodic table hydrogen understand the discovery of hydrogen know about the occurrence of hydrogen learn about the preparation, properties (physical and chemical) and uses of hydrogen understand oxidation and reduction reactions Warm-up Start the chapter by interacting with students about periodic table. Tell them to name a few elements metals or non-metals. Then, ask them the position of hydrogen in the periodic table and let them know that it is the most abundant of all elements in the universe. Make them aware about hydrogen propelled cars and how hydrogen can be used to fuel cars. Concept Explanation Finally, Lavoisier gave the name hydrogen after studying its properties. Let students know that the outer atmosphere of the sun and stars consists largely of hydrogen, whereas the outermost layer of earth s atmosphere has traces of it only. It is widely distributed in the combined state as in proteins, starch, sugar, petroleum, natural gas and coal. Preparation of Hydrogen Explain to the students that hydrogen can be prepared in the laboratory by Hydrogen: The Best Element Explain to the students that hydrogen is the lightest of all elements which contains only one proton and one electron (with atomic number 1) and no neutron. It is the rst element in the periodic table. Discovery of Hydrogen Make students aware of the fact that hydrogen was rst discovered in air by Robert Boyle but remained unidenti ed. Cavendish prepared this gas and named in ammable air . 68 a. Electrolysis of water, which should not be pure as pure water does not conduct electricity. Acidi ed or acidulated water (water mixed with some acids) conducts electricity and dissociates into hydrogen (H+) and hydroxyl ions (OH ). Hydrogen gas is released at the cathode and oxygen gas at the anode. b. By the action of dilute acids on metals Metals react with dilute HCl and dilute H2SO4 to form metal salts with the release of hydrogen. Zn + 2HCl ZnCl2 + H2 Explain to the students the reactivity series in which the metals are arranged in descending order of reactivity based on their reaction with acid. Generally zinc is preferred to other metals because it is more reactive and cheaper compared to other metals. Explain to the students the Industrial production of hydrogen by Bosch s Process, which involves passing steam over red hot coke at higher temperature. C + H2O (CO ) + H2 Heat To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. Properties of Hydrogen Explain to the students that hydrogen is a colourless odourless, tasteless, lightest gas which is almost insoluble in water. Also make them understand the chemical properties of hydrogen. It is neutral to litmus, is a combustible gas, reacts with chlorine, nitrogen, CO2, carbon, CO, sulphur and metals. It burns in air with a pop sound. To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. Uses of Hydrogen Explain to the students the use of hydrogen in weather balloons, hydrogenation of oils, in manufacture of chemicals, in oxy-hydrogen ame and as a fuel. Oxidation and Reduction Explain to the students the oxidation and reduction reaction involving hydrogen. Addition of hydrogen - Reduction Removal of hydrogen - Oxidation Activity: To show that hydrogen is a reducing agent. Hydrogen gas is passed through a U-tube lled with anhydrous calcium chloride. It removes moisture from the gas. The dry gas is then passed into a combustion tube. The combustion tube is closed at both ends with corks carrying delivery tubes. Copper oxide is kept in the combustion tube. It is clamped to a stand. The dry hydrogen gas coming out of the U-tube is passed into the combustion tube. Copper oxide is heated strongly. Reduction takes place. The water vapour coming out at the other end is condensed in a chilled beaker. To show that water is produced in the reaction, the liquid coming out is allowed to drop on anhydrous copper sulphate, which turns blue. Anhydrous copper sulphate is white while hydrated copper sulphate is blue in colour. Reactions involved: CuO + H2 Cu + H2O Thus, copper is left in the combustion tube and hydrogen reduces copper oxide to copper. Reinforce To reinforce, ask the students to read the Summary and Glossary sections and do the Exercises and Learning Zone sections from the textbook. Help students develop skills (research and thinking) given in the Skills for Life section in the chapter. Explore Ask students to do the Learn by Doing section given at the end of the chapter. 69 Worksheet 1 1. Explain the similarity of hydrogen with halogens. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 2. Write an equation showing hydrogen as reducing agent. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 3. Why is the helium gas used in weather balloons in place of hydrogen these days? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 4. Name the following. a. Water into which few drops of dilute acid are added. _____________ b. Gas used in weather balloons in place of hydrogen. _____________ c. Gas which burns in air with a pop sound. _____________ d. Gas that is released at the anode during the electrolysis of water. _____________ e. Conducting rods that allow electric current to enter and leave the electrolytic cell. _____________ 5. What is oxy-hydrogen ame? Where is it used? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 70 Worksheet 2 1. Look carefully at the picture given. a. Identify the element _________________________________________________ b. Write its symbol _________________________________________________ c. What is its atomic number and mass number? _____________________________________________________________________ d. What is its position in the periodic table? _____________________________________________________________________ e. Is it a metal or a non-metal? _____________________________________________________________________ 2. Draw a labelled diagram to show the electrolysis of water. 3. Name two metals that do not produce hydrogen gas with acids. Also give its reason. ________________________________________________________________________ ________________________________________________________________________ 4. Write a balanced equation for Haber Bosch process, indicating the conditions required for the reaction. Which gas is formed in this process? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 71 Answers to Coursebook PART I A 1. (b) 2. (a) 3. (c) 4. (d) 5. (a) B 1. Reducing agent 2. Acidulated 3. Presence 4. Reduced 5. Methane C 1. True 2. False 3. True 4. True 5. True 6. False 7. True 8. True 9 .False D 1. Water gas 2. Electrolytic Cell 3. Hydrogen 4. Metal hydrides 5. Hydrogen sulphide gas (H2S) E 1. 2NaH 2. CH4 + 2H2O + Energy 3. H2S 4. 2NH3 5. CH3OH water. CO2 + 4H2 CH4 + 2H2O + energy This reaction is called the Sabatier reaction. 2. a. In hydrogenation of oils- Solid vanaspati is obtained by passing hydrogen gas through an oil in the presence of nickel as a catalyst. b. In the manufacture of chemicals- Many important compounds like hydrochloric acid, methanol and ammonia are manufactured using hydrogen as a reactant. c. As a fuel- Liquid hydrogen, because of the high value of heat of combustion, is used as a rocket fuel. 3. a. Sodium Hydrogen reacts with sodium forming metal hydrides as shown by the following equation. H2(g) + 2Na(s) 2NaH (Sodium hydride) b. Sulphur PART II On passing hydrogen through boiling sulphur, hydrogen sulphide (H2S) gas is formed, which has the smell of rotten eggs. A 1. Antoine Lavoisier 2. The outer atmosphere of the sun and the stars consists largely of hydrogen. The outermost layer of the earth s atmosphere contains hydrogen, but in traces. But in the combined state, it occurs in water, starch, sugars, fats, proteins and other organic compounds. It is the main constituent of petroleum, natural gas and coal. H2 + S H2S c. Chlorine Hydrogen combines with chlorine violently, causing an explosion when the mixture is kept in bright sunlight. In di used light, the reaction is slow and hydrogen chloride is formed. 3. Ca, Mg 4. Hydrogen reduces copper oxide to copper. 5. Zn + H2SO4 ZnSO4 + H2 6. Hydrogen gas burns in air with a pop sound. B 1. Hydrogen reacts with carbon dioxide at elevated temperatures (optimally 300 400 C) and pressures in the presence of a nickel catalyst to produce methane and (Hydrogen sulphide) H2 + Cl2 2HCl 4. Hydrogen removes oxygen from metal oxides. This is called reduction and hydrogen is called a reducing agent. 72 CuO + H2 Cu + H2O Copper oxide Copper PbO + H2 Pb + H2O Lead oxide Lead 5. Solid vanaspati is obtained by passing hydrogen gas through an oil in the presence of nickel as a catalyst. This process is called hydrogenation of oil. On passing hydrogen, we get a saturated compound which is a solid and gives a better taste. 6. A reaction in which oxidation and reduction take place simultaneously is known as a redox reaction. Removal of oxygen: (reduction): CuO Cu Addition of oxygen (oxidation): H 2 H 2O Consider the reaction CuO +H2 Cu + H2O In the given reaction, CuO has eliminated oxygen from it to change to Cu. Thus, we can say that CuO has been reduced to Cu. But H2 has added oxygen to it to form H2O. Thus, H2 has been oxidised to H2O. Hydrogen is a reducing agent and copper oxide is the oxidising agent. We observe that reduction and oxidation have taken place simultaneously. There can be no reduction without oxidation and vice versa. 7. Dil. sulphuric acid or dil. hydrochloric acid is preferred over nitric acid in the laboratory preparation of hydrogen as nitric acid is a strong oxidising agent. C 1. Conical ask, thistle funnel, delivery tube, trough, beehive shelf, gas jar, two-holed rubber corks, dil. hydrochloric acid and zinc granules are required. Method: Granulated zinc is taken in the conical ask. It is closed with a two-holed rubber cork. Insert the thistle funnel and the delivery tube through the holes. The tail of the thistle funnel should reach the bottom of the ask. The delivery tube is passed into the beehive shelf kept immersed in water in the trough. Invert the gas jar lled with water over the beehive shelf. Pour dilute hydrochloric acid through the thistle funnel. If the reaction is very slow, a few 73 crystals of copper sulphate can be added to the ask and this acts as a catalyst and speeds up the reaction. Zn + 2HCl ZnCl2 + H2 Bubbles of hydrogen gas evolve briskly at the bottom of the ask, rising up from the surface of the zinc granules. The hydrogen gas is collected through the delivery tube in the gas jar by the downward displacement of water, as hydrogen is insoluble in water and lighter than water. The gas cannot be collected over air, as it is miscible in air. 2. Industrially, hydrogen is prepared by passing steam over red hot coke at a high temperature forming CO and hydrogen. This mixture of carbon monoxide and hydrogen is called water gas. C + H2O (CO) + H2 Heat It is diffcult to separate hydrogen from water gas. Therefore, to increase the production of hydrogen, the water gas is mixed with steam in the presence of iron chromate as a catalyst. The reaction produces a mixture of carbon dioxide and hydrogen gas. Iron chromate CO + H2 + H2O CO2 + 2H2 From this mixture, carbon dioxide is separated by passing through cold water or caustic potash solution. The CO2 dissolves in caustic potash solution or water and hydrogen is collected in cylinders. 3. Conical ask, boiling tube, U-tube, anhydrous calcium chloride, a jet, test tube, stand, hydrochloric acid, thistle funnel, zinc granules, a container are required. The conical ask contains granulated zinc. The delivery tube is passed into a U-tube containing anhydrous calcium chloride. The outlet from the U-tube is connected to a jet which passes into an inverted dry test tube clamped to a stand. Add hydrochloric acid into the ask through the thistle funnel. It is observed that Zinc reacts with dil. hydrochloric acid and releases hydrogen. reaction produces a mixture of carbon dioxide and hydrogen gas. This hydrogen is dried by passing it through anhydrous calcium chloride. As the gas starts evolving, bring a burning matchstick to the jet. Hydrogen starts burning at the jet with a blue ame. As the burning continues, water droplets are seen on the inner side of the test tube. They drop down into the container kept below the test tube. This activity shows that water is produced when hydrogen burns in air; it is also a test of hydrogen gas. chromate CO + H2 + H2O Iron CO2 + 2H2 d. Hydrogen is a combustible gas. It burns in air, producing water. 2H2 + O2 2H2O + Heat e. Hydrogen reacts with carbon at the temperature 520 C and above in the presence of nickel or cobalt and form hydrocarbons. Reactions involved: 2H2 + C CH4 Zn + 2HCl ZnCl2 + H2 Methane 5. a. 2Na + 2H2O 2NaOH + H2 Hydrogen b. 3Fe +4H2O Fe3O4 + 4H2 2H2 + O2 2H2O + Heat c. CuO + H2 Cu + H2O Thus, hydrogen burns with oxygen in air to form water, which is collected in the container after condensation. Cu/300 C d. CO + H2 CH3OH (Methyl alcohol) Fe/Mo, 200 atm 2NH e. N2 +3H2 3 4. a. Hydrogen combines with nitrogen in the ratio 3:1 by volume, in presence of catalyst iron and promoter molybdenum, at a pressure of 200 atmospheres and a temperature of 450 C, and gives ammonia. 200 atm Fe/Mo N2 + 3H2 2NH3 This process of manufacturing ammonia gas is known as the Haber Bosch process. b. Hydrogen reacts with carbon monoxide in the presence of powdered copper at 300 C, producing methyl alcohol. 6. a. Reduction b. Oxidation c. CuO d. Hydrogen D 1. Metals lying below hydrogen do not displace hydrogen when treated with HCl or H2SO4, while those placed above hydrogen displace hydrogen. So metals like Cu, Ag, Au are present below hydrogen and cannot displace hydrogen. 300 C, Cu 2H2 + CO CH3OH (Methyl alcohol) c. Industrially, hydrogen is prepared by passing steam over red hot coke at a high temperature. The products are CO and hydrogen. This mixture of carbon monoxide and hydrogen is called water gas. C + H2O (CO) + H2 Heat It is diffcult to separate hydrogen from water gas. Therefore, to increase the production of hydrogen, the water gas is mixed with steam in the presence of iron chromate as a catalyst. The 74 2. Hydrogen reacts with metals like sodium, potassium and calcium, forming metal hydrides as shown by the following equations. H2 + 2Na 2NaH (Sodium hydride) This is because it can show the valency as H +, H . 3. PbO + H2 Pb + H2O In the given reaction, PbO has eliminated oxygen from it to change to Pb. Thus, we can say that PbO has been reduced to Pb. But H2 has added oxygen to it to form H2O. Thus, H2 has been oxidised to H2O. Hydrogen is a reducing agent and lead oxide is the oxidising agent. We observe that reduction and oxidation have taken place simultaneously. 2. Anode and cathode: The negatively charged electrode is called cathode. When an electric current is passed through an electrolyte, the cations move towards cathode. While the positively charged electrode is called anode and the anions move towards anode. 4. Hydrogen reacts with oxygen inside the fuel cells, which produces electricity to power the motors. Bene t of large-scale deployment of hydrogen vehicles is that it could lead to decreased emissions of greenhouse gases and ozone precursors. 3. Oxidising and reducing agent: Substances that bring about oxidation are known as oxidising agents. Substances that bring about reduction are known as reducing agents. 5. Pure water does not conduct electricity because it has a negligible amount of ions. But when few drops of acid are mixed with some acid, it conducts electricity. This type of water is called acidi ed or acidulated water. On passing electric current through acidulated water, the dissociation of water takes place. E 1. Electrolysis: The process of the breaking down of an electrolyte chemically on the passage of electric current is called electrolysis. The process of electrolysis needs an electrolytic cell, an electrolyte, two electrodes and a power supply. Consider the reaction, CuO + H2 Cu + H2O Thus hydrogen is a reducing agent and copper oxide is the oxidising agent. LEARNING ZONE Picture based questions 1. a. Ammonia b. Catalyst iron and promoter molybdenum 2. Electrodes: Electrodes are conducting rods that allow electric current to enter and leave an electrolyte. They are usually made of inert or non-reactive substances so that they do not react with the electrolyte. Electrodes are of two types: anode and cathode. 3. Ions: When an electrolyte breaks down into positive and negative particles, the particles are called ions. Positively charged ions are called cations and negatively charged ions are called anions. c. Hydrogen combines with nitrogen in the ratio 3:1 by volume d. In the presence of catalyst iron and promoter molybdenum, at a pressure of 200 atmospheres and a temperature of 450 C. e. It shows that the reaction is reversible. f. Haber and Bosch 2. a. For the preparation of hydrogen 4. Hydrogenation: Solid vanaspati is obtained by passing hydrogen gas through an oil in the presence of nickel as a catalyst. This process is called hydrogenation. F 1. Oxidation and reduction: When a substance adds oxygen to it or eliminates hydrogen from it, the substance gets oxidised and this process is called oxidation. When a substance adds hydrogen to it or eliminates oxygen from it, the substance gets reduced. This process is called reduction. 75 b. A - Chilled dry test tube, B - Burning jet of hydrogen, C - Water droplets, D - Zn granules, E - HCl acid, F - Anhydrous calcium chloride c. The delivery tub from the conical ask is passed into one side of a U-tube containing anhydrous calcium chloride and the outlet from the U-tube is connected to a jet which passes into an inverted dry test tube clamped to a stand, so it is connected on both sides. d. This experiment shows that water is produced when hydrogen burns in air. e. Zn + 2HCl ZnCl2 + H2 delivery tube in the gas jar by the downward displacement of water, as hydrogen is insoluble in water and lighter than water. The gas cannot be collected over air, as it is miscible in air. 2H2 + O2 2H2O + Heat 3. a. Acidi ed water (dilute sulphuric acid) b. Test tube with cathode c. Oxygen gas O2(g) 1 volume of gas Hydrogen gas H2(g) 2 volumes of gas d. Pure water does not conduct electricity because it has negligible amount of ions. But water mixed with some acid conducts electricity and this type of water is called acidi ed or acidulated water. On passing electric current through acidulated water, the dissociation of water takes place. Think and answer 1. The hydrogen gas is collected through the 2. Hydrogen is a combustible gas. It burns in air, producing water. But when a large amount of hydrogen burns in air, it leads to an explosion. This is because hydrogen combines with oxygen violently. When made to burn at the end of a jet, it burns with a blue ame. 3. Liquid hydrogen, because of the high value of heat of combustion, is used as a rocket fuel. When a large amount of hydrogen burns in air, it leads to an explosion. This is because hydrogen combines with oxygen violently. When made to burn at the end of a jet, it burns with a blue ame. Answers to Worksheets WORKSHEET 1 WORKSHEET 2 1. Both hydrogen and halogens require one electron to complete their octets. For example H is 1s1 and F is 1s2 2s2 2p5. Hence, hydrogen can gain one electron to form a uni negative ion. Also, like halogens, it forms a diatomic molecule and several covalent compounds. 1. a. Hydrogen b. H c. Atomic number = 1 Mass number d. Hydrogen is the rst element in the periodic table. 2. CuO + H2 Cu + H2O Copper oxide Copper 3. This is due to the in ammable nature of hydrogen. 4. a. Acidulated water b. Helium c. Hydrogen d. Oxygen e. It is a highly reactive non-metal. 2. Refer gure 7.2 on page 112. 3. Cu, Hg, Au do not produce hydrogen gas with acids because these metals are present below hydrogen in the reactivity series and do not displace hydrogen when treated with HCl or H2SO4 4. N2 + 3H2 e. Electrode =1 5. A mixture of hydrogen and oxygen is called oxy-hydrogen ame, which when used in a welding torch, burns, giving a temperature of 2800-3000 C. This ame is used in cutting and welding of metals. 76 200 atm Fe/Mo 2NH3 Hydrogen combines with nitrogen in the presence of catalyst Iron and promoter molybdenum at 200 atmospheres and 450 C temperature. Ammonia is formed. 8 Water Learning Objectives Students will be able to: learn about water and its sources understand dissolution of salts in water know why water is a universal solvent learn about the different types of solutions know about the factors, affecting the formation of a solution differentiate between true solution, suspension and colloid understand water of crystallisation learn about reactivity of metals with water understand concept of hardness of water Warm-up Start the chapter by interacting with students regarding renewable and non-renewable resources. Water is a renewable resource and nearly three-fourth of the earth s surface is covered with water. Now discuss with them about the reaction of water with copper sulphate. Hydrated copper sulphate is always blue. On heating a sample of copper sulphate to dry it (forming anhydrous copper sulphate), we observe that it becomes white. Adding water will cause the colour to change back to a blue colour (i.e. hydrated form). Now, ask the students to complete the questions given in the Warm-up section. Concept Explanation Water and its Resources Explain to the students that water is a colourless, odourless and tasteless covalent compound formed by hydrogen and oxygen in the ratio of 2:1. Let them know that rainwater, surface water and groundwater are the major sources of water. Dissolution of salts in water Explain to the students how a solution is formed. When an ionic compound (like NaCl or salt) is dissolved in water, it undergoes a chemical change and when a covalent compound (like sugar) is dissolved in water, it does not result in a chemical reaction. Make students understand that water dissolves almost all substances on the earth and hence known as a universal solvent. Explain to the students different types of solution saturated, unsaturated and supersaturated and factors affecting the formation of a solution like temperature, stirring, particle size. 77 To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. True Solution, Suspension and Colloid Explain to the students the difference between true solution, suspension and colloid based on the size of the solute present in them. Explain to the students that when a beam of light is passed through a colloid kept in dark room, path of light through colloid become visible. This scattering of light by colloidal particles is called Tyndall effect. To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. Water of crystallisation Let them understand that there is a xed amount of water which is necessary for certain salts to crystallise from their aqueous solution. This is known as water of crystallisation. Reactivity of metals Explain to the students the reaction of metals with hot water, steam and cold water. Pb, Ni, Ag, Au show no reaction with water or steam. Metals such as potassium, calcium and sodium react with cold water vigorously, often catching re. They form hydroxides and hydrogen gas when they react with water. Magnesium metal reacts with hot water to form magnesium hydroxide and hydrogen gas. Metals such as magnesium, aluminium, zinc and iron react with steam vigorously and form oxides of metal and hydrogen gas. Hardness of water Explain to the students the difference between hard water and soft water. Hard water contains certain salts of Ca and Mg in large amounts and is not good for drinking. If hardness is temporary, it can be removed by boiling or adding lime, while permanent hardness can be removed by adding sodium carbonate or by ion exchange resins. Reinforce To reinforce, ask the students to read the Summary and Glossary sections and do the Exercises and Learning Zone sections from the textbook. Help students develop skills (research and thinking) given in the Skills for Life section in the chapter. Explore Ask students to do the Learn by Doing section given at the end of the chapter. 78 Worksheet 1 1. Give one word for the following. a. Foam produced when soap is rubbed with water. ________________ b. A solution which cannot dissolve any more solute at a given temperature. ________________ c. A transparent solution in which the solute is completely dissolved. ________________ d. Anhydrous solids that absorb moisture from air and form a solution. ________________ e. Colourless covalent compound, formed by the combination of hydrogen and oxygen. ________________ 2. Name the three physical forms of water. ________________________________________________________________________ ________________________________________________________________________ 3. Why is hard water not used for cooking? ________________________________________________________________________ ________________________________________________________________________ 4. Write the reactions of following metal with water a. Al _________________________________________________________________ b. Na _________________________________________________________________ c. Pb _________________________________________________________________ d. Cu _________________________________________________________________ 5. Why does table salt turn moist on exposure to air? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 79 Worksheet 2 1. Write the chemical names and formulas of the following. a. Gypsum _____________________________________________________ b. Glauber s salt _____________________________________________________ c. Green Vitriol _____________________________________________________ d. Plaster of Paris _____________________________________________________ e. Epsom Salt _____________________________________________________ 2. Differentiate between true solution and colloid on the basis of appearance and Tyndall effect. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 3. If 50 grams of a salt can be dissolved in 100 grams of water at room temperature, what is the solubility of the salt. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 4. How are blue crystals of copper sulphate formed? What happens when it is heated? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 5. What is the difference between hydrated salts and anhydrous salts? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 80 Answers to Coursebook Surface Water. Surface water comprises all the water bodies, such as oceans, seas, rivers and lakes, which are present on the earth s surface. PART I A 1. (c) 2. (c) 3. (b) 4. (a) 5. (d) B 1. Calcium and magnesium 2. Deliquescence 3. Covalent 4. Milk 5. Lime C 1. False 2. True 3. False 4. True 5. True 6. False D 1. Hard water 2. Ef orescence 3. Colloid 4. Solute 5. Solvent E 1. Solid 2. NaCl 3. Sulphuric acid 4. Ag 5. Lime Groundwater. When it rains, a part of the rainwater percolates down through the rocky layer and collects underground. This is called groundwater. 2. Water is a colourless, odourless and tasteless covalent compound, which is formed by the combination of hydrogen and oxygen. 3. A solid that dissolves in a liquid is called a solute. The liquid in which the solid dissolves is called a solvent. When a solid dissolves in a liquid, solution is formed. For example, in the case of common salt and water, salt is the solute and water is the solvent, and the resultant mixture is the salt solution. 4. The scattering of light by colloidal particles is called the Tyndall effect. When a strong beam of light is passed through a colloid kept in a dark room, the path of light beam through the colloid becomes visible. PART II A 1. When a saturated solution is cooled, its solubility decreases. This effect is used to determine whether a mixture is a true solution or a colloid. 2. a. Copper (II) sulphate CuSO4.5H2O 5. Certain substances also absorb moisture (water vapour) from the atmosphere, but not enough to form solutions. Such substances are called hygroscopic substances and the phenomenon is called hygroscopy. For example, silica gel b. Sodium carbonate Na2CO3.10H2O 3. When water contains certain salts of calcium and magnesium in large amounts, it doesn t produce lather with soap and causes hardness of water. Such substances are used as drying agents to remove moisture from other substances without chemically reacting with them. It is because of this that small silica gel packets are kept in bottles to keep them dry. 4. It is un t for dyeing clothes, as the dye will not x to the fabric due to the excess salt present in water. 5. Na, K 6. Al B 1. There are three main sources of water Rainwater. The primary source of water is rain. C 1. It is the ability of a solute to dissolve in a given solvent at a given temperature. 81 Factors Affecting the Formation of a Solution carbonates which precipitate out. a. Solubility increases with temperatureAt a given temperature, a saturated solution will become unsaturated on heating. On the other hand, solubility decreases as the solution is cooled. Ca(HCO3)2(aq) CaCO3 + H2O + CO2 b. Stirring- The rate of formation of a solution can be increased by stirring. c. Particle size- If the size of the solute is small, the rate of formation of the solution is faster. Mg(HCO3)2(aq) MgCO3 + H2O + CO2 This method is suitable only for small amounts of water because it is time consuming and expensive. Permanent hardness can be removed by the following methods. Calcium sulphate CaSO4.2H2O By adding sodium carbonate (washing soda). Sodium carbonate is added to hard water. It reacts with the soluble chlorides and sulphates of calcium and magnesium to produce insoluble carbonates which are ltered. The sodium chloride or sulphate formed does not interfere in the formation of foam. Copper (II) sulphate CuSO4.5H2O Na2CO3 + CaSO4 CaCO3 + Na2SO4 Ferrous sulphate FeSO4.7H2O Na2CO3 + MgCl2 MgCO3 + 2NaCl Zinc sulphate ZnSO4.7H2O Using permutit. Permutit is sodium aluminium silicate. When hard water is treated with permutit, the calcium and magnesium chlorides and sulphates are converted to sodium chloride and sodium sulphate and the hardness is removed. 2. Water of crystallisation is the xed amount of water which is necessary for certain salts to crystallise out from their aqueous solutions. Calcium sulphate semi-hydrate (CaSO4) . . H2O 3. When water contains certain salts of calcium and magnesium in large amounts, it doesn t produce lather with soap. Then, the water is said to be hard. The salts that cause the hardness of water are as follows. Calcium bicarbonate [Ca(HCO3)2] and magnesium bicarbonate [Mg(HCO3)2] they cause temporary hardness. Calcium chloride (CaCl2) and magnesium chloride (MgCl2) they cause permanent hardness. Ion exchange resins. These resins exchange calcium and magnesium ions with sodium ions, thereby removing the hardness. 4. a. Na reacts with cold water and catches re 2Na(s)+2H2O(l) 2NaOH(aq)+H2 b. Mg reacts with hot water and oats over water Mg(OH)2(aq) and H2(g) Mg(s) + 2H2O(hot) Mg(OH)2(s) + H2 Calcium sulphate (CaSO4) and magnesium sulphate (MgSO4) they also cause permanent hardness. Mg reacts with steam Removal of Hardness Mg(s) + H2O(g) MgO(s) + H2 Temporary hardness can be removed by boiling or adding lime. During boiling, calcium and magnesium bicarbonates decompose into insoluble carbonates, which settle at the bottom. When lime is added, the bicarbonates are converted to 82 c. Al reacts with Steam 4Al(s) + 6H2O(g) 2Al2O3(s) + 3H2 d. Fe reacts Steam 3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2 solvent. It can dissolve most minerals and nutrients present in our food and these dissolved materials are thus easily absorbed by the body. Water also dissolves the waste materials of the body, which are then removed by kidneys. Salts and metals also dissolve in water. e. Zn reacts with Steam Zn(s) + H2O(g) ZnO(s) + H2 f. Cu shows no reaction with water. 5. Water is called a universal solvent as it dissolves almost all substances on earth. It can dissolve most minerals and nutrients present in our food. These dissolved materials are thus easily absorbed by the body. Water also dissolves the waste materials of the body, which are then removed by kidneys. Salts and metals dissolve in water. There are many liquids that freely mix with water. It dissolves gases like oxygen, carbon dioxide, etc. Gases like sulphur dioxide, nitrogen dioxide, etc. dissolve in water to give acids. 2. Aluminium is highly reactive metal. When aluminium is exposed to air it reacts with oxygen and forms a white thin layer of aluminium oxide on its surface. This layer forms protective coating on aluminium and prevents the reaction of aluminium with oxygen. Aluminium metal with this protective layer is used for making cooking utensils. 3. Blue crystals of CuSO4.5H2O are formed by the chemical combination of 1 mole of CuSO4 with 5 moles of H2O. When heated, it loses the water of crystallisation (i.e., 5 moles) and forms a white powder, CuSO4. D 1. Supersaturated Solution: A solution that contains more solute than the solvent can dissolve at a speci c temperature is known as a supersaturated solution. 2. True solution: A true solution is a homogeneous mixture of two or more substances in which a substance dissolved (solute) in solvent has the particle size of less than 10 9 m or 1 nm. A simple solution of sugar in water is an example of true solution. 4. Hard water produces boiler scales in gas boilers. Boiler scales are produced due to the deposition of salt on the walls of the boiler, as the dissolved salts crystallise when water evaporates. 5. As temperature rises, more and more solute can dissolve in the solvent. In other words, on heating to a higher temperature, a saturated solution becomes unsaturated. 3. Tyndall Effect: The scattering of light by colloidal particles is called the Tyndall e ect. 4. Suspension: A suspension is heterogeneous and the particle size is large enough to be seen with naked eyes. A suspension is opaque. 5. Colloid: In colloids, particles are partially visible. Colloids are translucent. They are homogeneous as they pass through the lter paper; the solid phase cannot be separated from the liquid phase. 6. Water of crystallisation: It is the xed amount of water which is necessary for certain salts to crystallise out from their aqueous solutions. This water makes it possible for them to form crystals. F 1. Substances which lose the water of crystallisation when exposed to air are called efforescent substances and the phenomenon is called e orescence, whereas the substances which absorb water when exposed to the atmosphere and become moist, hence, ultimately, they turn into solutions by absorbing water are called deliquescent and the phenomena is called deliquescence. E 1. Water dissolves almost all substances on earth. That is why it is called a universal 83 2. True solution is homogeneous, clear and transparent. Particles of solute are invisible. Colloid is heterogeneous, cloudy and translucent. Particles can be seen with the help of a powerful microscope. True solutions do not scatter light whereas light is dispersed by a colloidal solution. 3. Permanent hardness is caused by chlorides and sulphates of calcium and magnesium. Calcium bicarbonate [Ca(HCO3)2] and magnesium bicarbonate [Mg(HCO3)2] cause temporary hardness. 4. A solution in which no more solute can dissolve at a speci c temperature is called a saturated solution whereas a solution that contains more solute than the solvent can dissolve at a speci c temperature is known as a supersaturated solution. 5. The salts containing the water of crystallisation are known as hydrated salts. On heating, they lose the water of crystallisation and are called anhydrous salts. LEARNING ZONE Think and answer 1. Detergents work well with hard water. When a soap is used in hard water, a solid substance called scum is formed. This is because charged calcium and magnesium particles (called ions) present in the water react with soap to form an insoluble substance. Scum builds up on clothes, baths and sinks. Detergents do not form scum. They are made from propene (formula CH3 CH=CH2) a compound from distilling crude oil. A complicated series of reactions turns propene into a detergent. Like soap, detergent molecules have a long chain of carbon and hydrogen atoms, but at the end of the molecule there is this group. -SO3 Na+ instead of the - COO Na+ group present in soap. This difference stops scum forming. Picture based questions 1. a. A. If the size of the solute is small, the rate of formation of the solution is faster. b. E, because solubility temperature. iii. Hard water is not good for drinking, as it may cause kidney stones. increases with c. F, because solubility decreases as the solution is cooled. d. We can get back the solute by heating the solution till all the solvent evaporates. e. On increasing the temperature. 2. a. A hard water B soft water b. By boiling or adding lime. During boiling, calcium and magnesium bicarbonates decompose into insoluble carbonates, which settle at the bottom. When lime is added, the bicarbonates are converted to carbonates which precipitate out. 2. Water puri cation removes harmful contaminants from water. Filtration, which physically blocks or chemically removes contaminants, is a different puri cation technique from reverse osmosis, which lters water through a semi-permeable membrane, and distillation, which vaporizes water to separate it from the contaminants. Domestic Carbon lters are very effective at removing a number of deleterious chemicals. These include chlorine, benzene, radon, solvents trihalomethane compounds, volatile organic chemicals such as pesticides and herbicides and hundreds of other man-made chemicals that may come into contact with tap water as it proceeds through the system. In addition, lters remove bad tastes and odours from water. c. i. Hard water doesn t give lather with soap. As a result, a lot of soap is wasted and clothes will not be cleaned of stains. ii. If hard water is used for cooking, it takes a longer time to cook and there is a wastage of fuel. 84 Carbon lters are not particularly successful at removing dissolved inorganic contaminants and heavy metals such as minerals, salts, antimony, arsenic, asbestos, barium, beryllium, cadmium, chromium, copper, uoride, mercury, nickel, nitrates, selenium, sulfate, thallium and other contaminants, which may require a reverse osmosis system or distiller instead. 3. The World Health Organization says that there does not appear to be any convincing evidence that water hardness causes adverse health effects in humans . In fact, it has been found that hard water actually serves as a dietary supplement for calcium and magnesium. Recommendations have been made for the maximum and minimum levels of calcium (40 80 ppm) and magnesium (20 30 ppm) in drinking water. Answers to Worksheets WORKSHEET 1 d. Calcium sulphate semi hydrate (CaSO4) . H 2O 1. a. Lather e. Magnesium sulphate - MgSO4 . 7H2O b. Saturated solution 2. c. True solution d. Deliquescence e. Water 2. Solid, liquid, gas 3. Hard water is not used for cooking as it takes a longer time to cook and there is a wastage of fuel. 4. a. 4Al(s) + 6H2O(g) 2Al2O3(s) + 3H2 b. 2Na(s) + 2H2O(l) 2NaOH(aq) + H2 c. Pb + H2O No reaction d. Cu + H2O No reaction 5. On exposure to air, table salt (NaCl) turns moist and forms a solution, especially during the rainy season because it contains impurities like MgCl2 and CaCl2 which are deliquescent. NaCl is not deliquescent. WORKSHEET 2 1. a. Calcium Sulphate CaSO4 . 2H2O b. Sodium sulphate Na2 SO4 . 10H2O Property True solution Colloid 1. Appearance Homogeneous, Heterogeneous clear and trans- and translucent parent 2. Tyndall effect Do not scatter light Light is dispersed by a colloidal solution 3. 50%, as the solubility is expressed as a percentage. 4. The blue crystals of copper sulphate are formed by the chemical combination of 1 mole of CuSO4 with 5 moles of H2O.CuSO4. 5H2O When heated, it loses the water of crystallisation (i.e. 5 moles) and forms a white power, CuSO4. 5. The salts containing the water of crystallisation are known as hydrated salts. On the other hand, when hydrated salts lose the water of crystallisation on heating, they form anhydrous salts. For e.g. c. Ferrous Sulphate FeSO4 . 7H2O CuSO4 . 5H2O hydrated salt CuSO4 85 anhydrous salt 9 Carbon and its Compounds Learning Objectives Students will be able to: learn about carbon and its allotropes differentiate between crystalline and amorphous forms of carbon. know the examples, physical properties and uses of crystalline forms of carbon and amorphous form of carbon understand the preparation, properties, tests and uses of CO2 learn about Greenhouse effect and global warming. know properties of carbon monoxide. Warm-up Start the chapter by discussing metals and non-metals in the periodic table. Take the example of carbon. Let them recollect that carbon is an element of immense signi cance to us in both its elemental form and in the combined form. It is a versatile element that forms the basis for all living organisms and many of the things we use. For example, wood, paper and cream Concept Explanation Carbon and its Allotropes Explain to the students that carbon is a nonmetal and is the sixth element in the periodic table with atomic number 6 and atomic mass 12. Make them understand that carbon forms a large number of inorganic and organic compounds and exists in two allotropic forms crystalline and amorphous. Explain to the students the various crystalline forms of carbon, starting with diamond. In this, each carbon atom is linked to 4 other carbon atoms to form a tetrahedron and many such units fuse together and form a three dimensional molecule giving octahedral shape. Diamond is the hardest substance known, transparent, good conductor of heat, chemically inert substance. It is used in cutting machines, drilling tools in manufacture of thin wires and in jewellery. Graphite. Graphite is soft, greyish black, opaque substance, insoluble in most solvents and good conductor of heat and electricity. In graphite, each c-atom is linked to other three other carbon atoms to form hexagonal rings, which further form a layer. It is used as pencil lead, electrodes in batteries, lubricant for machines, moderator in nuclear reactors. Fullerene. Fullerene are more active than diamond and graphite chemically. In this, many (30-900) carbon atoms are held together in cage-like structure. They also occur in cylindrical form known as carbon 86 nanotubes. Fullerenes are used as catalyst, semi-conductors in computers, and are super conductors. To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. Explain to the students the amorphous forms of carbon charcoal soft, porous solid is formed when wood, sugar or bone is heated in the absence of air in a closed container. Make the students aware about different uses of charcoal. Coal. Coal is a fossil fuel formed when vegetation buried due to natural calamities, under high temperature and pressure was converted into coal. Let students know that based on the carbon content, it is divided into 4 types peat, lignite, bituminous, anthracite. Explain to them the different uses of coal. Soot. This form of carbon has 98-99% carbon and is prepared by heating carbonrich substances. It is collected in the form of black powder and also known as lamp black. CaCO3 + 2HCl CaCl2 + CO2 + H2O Calcium Explain to the students that CO2 occurs in free state in air. It can be prepared by heating metal carbonates, heating metal bicarbonates, burning carbon, reaction of dilute acids with metal carbonates. Make them understand, the preparation of CO2 in the laboratory, by the following equation. Carbon Water dioxide Explain to the students that CO2 is colourless, odourless gas which does not support combustion and forms a white solid called dry ice when cooled to 70 C. Make them understand the chemical properties also. A covalent compound, turns blue litmus red. Dissolves in water CO2 + H2O H2CO3 (Carbonic acid) Also dissolves in water under pressure e.g. soda and aerated drinks. Reacts with alkalis 2NaOH + CO2 Na2CO3 + H2O (Neutralisation reaction) Coke. Purest form of carbon, produced by heating bituminous coal to a high temperature in the absence of air. Used to prepare producer gas and water gas. Carbon Dioxide Calcium Chloride Explain to the students the test of CO2. When CO2 is passed through lime water, it turns milky due to the formation of calcium carbonate. Milkiness disappears due when excess of CO2 is passed due to formation of calcium bicarbonate. Also, a burning matchstick or a candle when put in a jar of CO2, gets extinguished. Gas carbon. A grey solid prepared by the destructive distillation of coal. To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook. Hydrochloric acid Mg burns in CO2 2Mg + CO2 2MgO + C Reacts with hydrogen 3CO2 + 6H2 CH4 + 2CO+C Methane Explain to the students the various uses of CO2 in soft drinks, storage of food, in medical eld, in re extinguishers. Greenhouse Effect Explain to the students that some of the radiations from the sun are trapped by CO2 in the air making the earth warm. This is known as Greenhouse effect . As the amount of CO2 is increasing in the air due to the 87 pollution and due to other green house gases in air, more heat is being trapped, increasing the greenhouse effect and further warming of the earth. This is known as global warming. limited supply of air. Make students aware of the harmful effects of CO. Make them aware of the effects of the global warming that how Gangotri glacier in the Himalayas has started melting and ecological balance is being disturbed. Carbon Monoxide To reinforce, ask the students to read the Summary and Glossary sections and do the Exercises and Learning Zone sections from the textbook. Help students develop skills (research and thinking) given in the Skills for Life section in the chapter. Explain to the students about a poisonous gas carbon monoxide Explore 2C + O2 2CO It is formed when carbon burns in a Reinforce Ask the students to do the Learn by Doing section given at the end of the chapter. 88 Worksheet 1 1. a. Identify the allotrope of carbon. _____________________________________________________ _____________________________________________________ b. How are carbon atoms held together? _____________________________________________________________________ _____________________________________________________________________ c. What happens when it is heated to about 1000 C? _____________________________________________________________________ _____________________________________________________________________ d. Give two uses of this allotrope of carbon. _____________________________________________________________________ _____________________________________________________________________ e. Give most common example of this allotrope. _____________________________________________________________________ _____________________________________________________________________ 2. Give two examples of organic compounds formed by carbon. ________________________________________________________________________ ________________________________________________________________________ 3. Give two examples of the compounds of carbon in combined state. a. In solid state _____________________________________________________________________ b. In liquid state _____________________________________________________________________ c. In Gaseous state _____________________________________________________________________ 89 Worksheet 2 1. Complete the following. Carbon Graphite Coal 2. a. Which gas is produced when carbon burns in a limited supply. _____________________________________________________________________ b. Write a balanced equation for this. _____________________________________________________________________ c. What happens when it is inhaled in large quantities. _____________________________________________________________________ 3. Name four greenhouse gases ________________________________________________________________________ ________________________________________________________________________ 4. Why is CO2 used in re extinguishers ________________________________________________________________________ ________________________________________________________________________ 5. What is destructive distillation? a. What is formed as a residue? b. Name the gases formed in this process ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 90 Answers to Coursebook PART 1 A 1. (b) 2. (c) 3. (c) On each carbon atom, one electron is free which makes graphite a good conductor of electricity. 4. (a) 5. (d) 3. Bituminous is the most common variety of coal. B 1. Fossil fuels 2. Dolomite 4. Fullerene is the crystalline form of carbon. In fullerenes, many carbon atoms are held together in a cage-like structure. 3. Hydrocarbons 4. Carboxy haemoglobin 5. When charcoal is heated, it forms activated charcoal. Activated charcoal is more porous than charcoal. 5. Allotropy 6. Diamond 6. Coke is used for manufacturing steel and extracting many metals. 7. Fullerenes 8. Carbonisation C 1. True 2. True 3. True 4. True 5. True 6. False 7. True 8. False 9. False D 1. (e) 2. (a) 3. (g) 5. (b) 6. (d) 7. (f) 7. CO2 forms a white solid called dry ice when cooled to 70 C. On heating, dry ice sublimes to form gaseous carbon dioxide. 8. Carbon dioxide is used in re extinguishers as it is not a supporter of combustion. 4. (c) B 1. The process of heating organic substances strongly in the absence of air is known as destructive distillation. E. 1. Destructive distillation 2. Fullerenes In the process of destructive distillation of wood, wood charcoal is formed. Charcoal is formed as a residue, and carbon dioxide, carbon monoxide, methane and hydrogen gases are also formed. The mixture of these gases is combustible and is known as wood gas. 3. Activated charcoal 4. Coke 5. Coke 6. Diamond 7. Carbon dioxide F. 1. Graphite 2. An organic compound is virtually any chemical compound that contains carbon. 2. Soot Methane is the simplest organic compound. Other examples include Ethyl alcohol- C2H5OH, Acetic acid CH3COOH. 3. Lactose 4. Oxalic acid PART 2 A 1. The reason for the brilliance of a diamond is its cutting and polishing. 2. In graphite, each carbon atom is linked to three other carbon atoms to form hexagonal rings which forms a layer. Several such layers are held together by a weak force. 91 3. When carbon monoxide (CO) gas reacts with oxides of zinc, iron, lead or copper, they are reduced to metals and carbon dioxide (CO2) is formed. ZnO + CO Zn + CO2 PbO + CO Pb + CO2 4. Lime water contains calcium hydroxide. It reacts with carbon dioxide, forming calcium carbonate, which is insoluble in water and remains as a precipitate. That s why lime water turns milky. 5. The trapping of the earth s radiated energy by carbon dioxide present in the air, so as to keep the earth warm, is called greenhouse e ect . 6. It is a colourless, odourless gas, fairly soluble in water. It is 1.5 times heavier than air. It is neither combustible nor a supporter of combustion. That is why carbon dioxide gas is used in extinguishing res. It forms a white solid called dry ice when cooled to 70 C. On heating, dry ice sublimes to form gaseous carbon dioxide. 7. Soot is a light, black powder which contains 98 99% carbon. It is prepared at home by heating carbonrich substances like turpentine oil or kerosene oil in a limited supply of air. The oil burns with a sooty ame that contains large amounts of free carbon. The black smoke is collected in the form of black powder. 8. Wood charcoal serves as an e cient fuel because it burns at a low temperature without producing smoke. It is an important constituent of gunpowder. It is used in gas masks to absorb harmful gases. C 1. Refer Figure 9.4 and 9.7 In diamond, each carbon atom is linked to 4 other carbon atoms to form a tetrahedron. Many such tetrahedral units are fused together and form a three dimensional molecule. This makes it very rigid, and it is di cult to break the C C link. The shape of the crystal is octahedral. On the other hand in graphite, each carbon atom is linked to three other carbon atoms to form hexagonal rings. Many such rings together form a layer. Several such layers are held together by 92 a weak force. On each carbon atom, one electron is free. This free electron accounts for the electrical conductivity of graphite. The layers can slide over one another, which makes it soft and soapy to touch. Thus, there occurs difference in hardness and electric conductivity. 2. Coal was formed when vegetation was buried due to natural calamities, such as earthquakes and volcanic eruptions, and was trapped inside the deeper layers of the earth for millions of years. Under high temperature, high pressure and less supply of oxygen, it was converted into coal which is actually a fossil. The slow process of conversion of wood into coal is called carbonisation. Based on the carbon content, coal is divided into four categories: Peat: This variety of coal contains about 50 60% of carbon. It is the rst stage of the formation of coal. It is light brown in colour. Lignite: This variety of coal contains more than 60% of carbon. This marks the second stage in the formation of coal. It is also brown in colour although it is harder than peat due to greater carbon content. Bituminous: This variety contains 90%, 80% and 70% carbon depending upon whether it is of high, medium or low quality. This variety marks the third stage in the formation of coal. This variety is the most common and is known as household coal. Anthracite: It is the last and fourth stage in the formation of coal. It contains 92 98% carbon. It is hard, black and dense. 3. CO2 is prepared in laboratory by the following method. Things needed. A Woulfe s bottle, corks, delivery tube, thistle funnel, gas collecting jar with lid, marble chips and dilute hydrochloric acid. Instead of the Woulfe s bottle, a conical ask can be used. Method. Take marble chips in the Woulfe s bottle. Close it with the cork. Pass a thistle funnel and delivery tube through the holes in the cork. Pass the other end of the delivery tube into the gas collecting jar. The tail of the thistle funnel should reach the bottom of the ask. Pour dilute hydrochloric acid through the thistle funnel. There is brisk e ervescence and the gas evolved collects in the gas jar. The following reaction takes place. CaCO3 + 2HCl CaCl2 + CO2 + H2O Carbon dioxide being heavier, displaces air upward and occupies the gas jar. 4. The trapping of the earth s radiated energy by carbon dioxide present in the air, so as to keep the earth warm, is called greenhouse e ect . Due to air pollution, the total amount of carbon dioxide in air has increased. Besides that, there are other greenhouse gases in air due to pollution, such as nitrous oxide, ozone, chloro uorocarbon, methane, etc. All these gases have created a thermal blanket around the earth, trapping more heat and increasing the greenhouse effect. This causes further warming of the earth, known as global warming. Refer gure 9.19 from the textbook. 5. Charcoal, coal, soot, gas carbon and coke are the amorphous forms of carbon. a. Charcoal-Charcoal is a black, soft and porous solid. When organic substances such as wood, bone or sugar are heated strongly in the absence of air in a closed container, then charcoal is formed. Uses-Wood charcoal serves as an e cient fuel because it burns at a low temperature without producing smoke. It is an important constituent of gunpowder. It is used in gas masks to absorb harmful gases. It is used in the form of tablets given to patients su ering from gastric problems and indigestion. Because of its adsorptive action, it removes stomach gases and provides relief. It is used in the sugar industry to decolourise sugar. b. Coal-It is a fossil fuel. It was formed 93 when vegetation was buried due to natural calamities, such as earthquakes and volcanic eruptions, and was trapped inside the deeper layers of the earth for millions of years. Under high temperature, high pressure and less supply of oxygen, it was converted into coal which is actually a fossil. Based on the carbon content, coal is divided into four categories: Peat, Lignite, Bituminous, Anthracite. Uses -Coal nds use as a domestic and industrial fuel. It is used in the manufacture of synthetic petrol. It is used as a source of a number of organic compounds such as benzene, naphthalene, etc. and is used to prepare coke, coal gas and coal tar. c. Soot (Lamp Black)- Soot is a light, black powder. It contains 98 99% carbon. It is prepared by heating carbonrich substances like turpentine oil or kerosene oil in a limited supply of air. Uses -It is used in making black shoe polish, carbon paper, printing ink, black paint, etc. It is also used in cosmetics. d. Gas Carbon- It is prepared by the destructive distillation of coal or when petroleum products are heated at high temperatures in a closed container. Uses -It is used for making the electrodes of dry cells and carbon rods for arc lamps. It is also a good conductor of electricity. e. Coke- It is a tough, porous and black coloured substance, which is the purest form of carbon. It has high carbon content and it burns with very little or no smoke. Uses -Coke is used for manufacturing steel and extracting many metals. It is also used to prepare gaseous fuels, such as producer gas (nitrogen and carbon monoxide) and water gas (hydrogen and carbon monoxide). 6. Fullerenes is an Crystalline form of carbon. It is black in colour and hard. In fullerenes, many carbon atoms are held together in a cage-like structure. (The number of carbon atoms vary between 30 and 900.) In the most common fullerene, called buckminster fullerene or buckyball, 60 carbon atoms are arranged in a spherical structure. 5. Anthracite- It is the last and fourth stage in the formation of coal. It contains 92 98% carbon. It is hard, black and dense. Although it is di cult to ignite, but once ignited, it gives a lot of heat which lasts for a long time. 6. In fullerenes, many carbon atoms are held together in a cage-like structure. Cylindrical fullerenes are called carbon nanotubes. Physical properties. Fullerences are soluble in organic solvents. Their speci c gravity ranges from 1.8 to 2.1 g/cm3. Chemically, fullerenes are more active than diamond and graphite. On heating to around 1000 C, the cagelike structure of fullerenes collapses. Uses- Fullerenes act as insulators. Some of the fullerenes are superconductors. They are used as catalysts. They are used as semiconductors in computers and TVs. E. 1. CO is the enemy of man. It is a poisonous gas. When inhaled in large quantities, it leads to death. CO combines with the haemoglobin of the blood to form carboxy haemoglobin, which stops the absorption of oxygen by blood and the respiratory system fails. D 1. Allotropy is the existence of a chemical element in two or more forms, which may di er in the arrangement of atoms in crystalline solids or in the occurrence of molecules that contain di erent numbers of atoms in the same physical state. The di erent forms of an element are known as allotropic forms or allotropes. All the allotropes of an element have the same chemical properties but di erent physical properties. 2. CO2 forms a white solid called dry ice when cooled to 70 C. On heating, dry ice sublimes to form gaseous carbon dioxide. 3. Carbon Monoxide is a colourless, odourless and highly poisonous gas. It is formed when carbon burns in a limited supply of air. 2C + O2 2CO 4. Bituminous is a type of coal which contains 90%, 80% and 70% carbon depending upon whether it is of high, medium or low quality. It marks the third stage in the formation of coal. This variety is the most common and is known as household coal. 94 2. Carbon dioxide molecules are heavier than air. Because of this, they push the oxygen and other molecules in the air out of the way as they sink down over the ame, due to which the ame is put out. 3. Coal and petroleum are called nonrenewable resources as these are those resources that are limited in quantity and cannot be replaced quickly after use. Coal and petroleum are produced organically which is why they are classi ed as fossil fuels. 4. When coal oven and coal gas are used for cooking, there should be proper ventilation as CO produced, is a poisonous gas. When inhaled in large quantities, it leads to death. 5. Carbon dioxide is harmless when breathed in small quantities but death may result from suffocation when inhaled in large quantities because it prevents oxygen from reaching the lungs. 6. Diamond is an allotrope of carbon. It is very hard and have high refractive index. Hence it is used in jewellery. It has lustre ,and is less reactive, Diamond used in jewellery is most expensive because, when cut by experts, it will sparkle and re ect light in an attractive way. F 1. Graphite and Diamond: Diamond is transparent and brilliant. Its density is 3.5 g/cm3. It is a good conductor of heat but a bad conductor of electricity. It is the hardest material known. It burns at 850 1000 C in air, giving carbon dioxide. It is chemically inert. 4. Charcoal is a black, soft and porous solid. When organic substances such as wood, bone or sugar are heated strongly in the absence of air in a closed container, then charcoal is formed. Coke is a tough, porous and black coloured substance, which is the purest form of carbon. It has high carbon content and it burns with very little or no smoke. It is produced by heating bituminous coal to a very high temperature in the absence of air. Coke can be obtained naturally or it can be prepared arti cially as well. On the other hand, graphite is soft and greasy to touch. It is a greyish black, opaque substance with metallic lustre. It has a density of 2.39 g/cm3. It is stable to heat and has a very high melting point of 3700 C. It is a good conductor of heat and electricity. It is insoluble in most solvents. It burns in air at 800 C to form carbon dioxide. 5. Charcoal is a black, soft and porous solid. When organic substances such as wood, bone or sugar are heated strongly in the absence of air in a closed container, then charcoal is formed. 2. Coal and Coke: Coal is a fossil fuel. It was formed when vegetation was buried due to natural calamities, such as earthquakes and volcanic eruptions, and was trapped inside the deeper layers of the earth for millions of years. Under high temperature, high pressure and less supply of oxygen, it was converted into coal which is actually a fossil. When charcoal formed is heated further, it forms activated charcoal. Activated charcoal is more porous than charcoal. 6. It is a colourless, odourless and highly poisonous gas. Carbon monoxide is formed when carbon burns in a limited supply of air. Coke It is a tough, porous and black coloured substance, which is the purest form of carbon. It has high carbon content and it burns with very little or no smoke. It is produced by heating bituminous coal to a very high temperature in the absence of air. Coke can be obtained naturally or it can be prepared arti cially as well. 3. Crystalline and Crystalline form of amorphous form of carbon A m o r p h o u s carbon form of carbon They have a de nite geometric shape when broken, and each piece has a sharp edge and plane surfaces. They do not have a de nite form. When cut or broken, the pieces are not similar and have no sharp edges or plane surfaces 2C + O2 2CO CO support combustion and burn with pale blue ame. CO2 is a colourless, odourless gas, fairly soluble in water. It is 1.5 times heavier than air. It is neither combustible nor a supporter of combustion. LEARNING ZONE Picture based questions 1. a. A Lignite, B- Peat, C- Bituminous, DAnthracite b. Lignite - more than 60% of carbon, Peat 50 60% of carbon, Bituminous 90%, 80% and 70% carbon depending upon whether it is of high, medium or low quality, Anthracite - 92 98% carbon They have a de nite They have no de nite melting point. melting point c. Bituminous For example, For example, coal, diamond, graphite charcoal and coke. and fullerene. d. Peat 95 2. a. Apparatus used for distillation of wood. the destructive b. 1. pieces of wood 2. wood gas 3. tar c. Charcoal d. Charcoal serves as an e cient fuel because it burns at a low temperature without producing smoke. 3. a. If a burning candle is put in the jar of carbon dioxide, it gets extinguished. b. If the length of the candle is more, it is in contact with air more and thus continue burning. c. It is neither combustible nor a supporter of combustion. Think and answer 1. Due to increase in CO2, ice in polar regions may melt, causing oods in coastal regions and islands. The Gangotri glacier in the Himalayas has already started melting. It would cause disturbance in ecological balance. It could result in wide ranging e ects on rainfall patterns, agriculture, forests, etc. Extinction of many species of plants and animals may also take place. One way to reduce the amount of carbon dioxide in the air is to burn less fossil fuels. Unfortunately, we depend on the burning of fossil fuels for heating, electricity generation and transport. If we are to burn less fossil fuels, we will need alternatives for these essential activities. We can t all buy 100% organically and locally produced items that have been created with renewable energy all the time, so try to purchase green tags to help offset carbon dioxide emissions. 2. The property that is used in making jewellery is the transparency of substance and re ection of light. Graphite does not possess these properties. It is soft, black and opaque. Unlike diamond which is transparent, hard and re ect light. So, graphite is not used for making jewellery. Answers to Assessment 2 A 1. (a) 2. (d) 3. (b) 4. (c) heated strongly in the absence of air or in a limited supply of air to obtain the oxide by removing CO2 and H2O. 5. (b) B 1. It is brown in colour and marks the second stage in the formation of coal. It contains 60% of carbon. C 1. (c) 2. (a) 4. (b) D. 1. Carbon monoxide 2. CO2 forms a white solid when cooled to 70 C. It is known as dry ice. 2. Potassium dichromate 3. When it rains, some part of it percolates down through the rocky layer and collects underground. This is called groundwater. Hand pumps, springs, wells are the sources of ground water. 3. Hydrated 4. It is a reaction in which a more reactive element displaces a less reactive element from a compound and takes its place. 3. (d) permanganate, potassium 4. Charcoal 5. Carbonisation E 1. When two or more elements or compounds chemically combine to form a new product, it is called a synthesis or combination reaction. For e.g. Fe + CuSO4 Cu + FeSO4 Calcination is a decomposition reaction. It is the process in which metal ores are 96 C + O2 CO2(g) + Heat Whereas when on heating, a compound breaks up into elements or simpler 2. 3. F 1. 4. G 1. 2. compounds is called the decomposition of the substance and such reactions are called decomposition reactions. CaCO3 heat CaO + CO2(g) Temporary hardness which is caused by Calcium and magnesium bicarbonate i.e. [Ca(HCO3)2] and [Mg(HCO3)2]. It can be removed by boiling or adding lime. During boiling, calcium and magnesium bicarbonates decompose into insoluble carbonates, which settle at the bottom. When lime is added, the bicarbonates are converted to carbonates which precipitate out. This method is suitable only for small amounts of water because it is time consuming and expensive. On the other hand, permanent hardness is caused by chlorides and sulphates of calcium and magnesium. It can be removed by adding sodium carbonate (washing soda), using permutit (sodium aluminium silicate) or ion exchange resins. Carbon dioxide occurs in free state in air. It constitutes 0.03% 0.04% by volume of air. Carbon dioxide is fairly soluble in water. All water bodies, such as oceans, lakes, rivers, etc., contain dissolved carbon dioxide. It is produced in respiration. Atmospheric carbon dioxide is used by plants in the preparation of food during photosynthesis. On the other hand, carbon monoxide is a colourless, odourless and highly poisonous gas. Carbon monoxide is formed when carbon burns in a limited supply of air. 2C + O2 2CO True 2. True 3. False True 5. True Any element or compound which helps in the addition of oxygen or an electronegative element or the removal of hydrogen or an electropositive element is called an oxidizing agent. An oxidising agent brings about an oxidation reaction. Fe2O3 + 3CO 2Fe + 3CO2 Here, ferric oxide is reduced and carbon monoxide is oxidised. Carbon monoxide is a reducing agent. 3. Solid vanaspati is obtained by passing hydrogen gas through an oil in the presence of nickel as a catalyst. This process is called hydrogenation. 4. Water dissolves almost all substances on earth. That is why it is called a universal solvent. It can dissolve most minerals and nutrients present in our food. These dissolved materials are thus easily absorbed by the body. Water also dissolves the waste materials of the body, which are then removed by kidneys. Salts and metals dissolve in water. 5. Factors Affecting the Formation of a Solution Solubility increases with temperature Stirring Particle size 6. a. It is transparent and brilliant. The brilliance and beauty of a diamond depends on its cutting and polishing. b. It is a good conductor of heat but a bad conductor of electricity. 7. Fullerene is crystalline form of Carbon. In fullerenes, many carbon atoms are held together in a cage-like structure. The number of carbon atoms vary between 30 and 900. Fullerenes show variable properties depending upon the number of carbon atoms. H 1. The process of heating organic substances strongly in the absence of air is known as destructive distillation. 97 In the process of destructive distillation, wood charcoal and bone charcoal are formed, depending upon the material used. Charcoal is formed as a residue, and carbon dioxide, carbon monoxide, methane and hydrogen gases are also formed. The mixture of these gases is combustible and is known as wood gas. When charcoal is heated further, it forms activated charcoal. 2. A few uses of coal are. Coal nds use as a domestic and industrial fuel. It is used in the manufacture of synthetic petrol. 5. Characteristics of a chemical reaction a. Evolution of Gas It is used as a source of a number of organic compounds such as benzene, naphthalene, etc. 2Na + 2HCl 2NaCl + H2 b. Change in Colour When ferric chloride solution is mixed with sodium hydroxide solution, a brown precipitate is obtained. It is used to prepare coke, coal gas and coal tar. 3. a. Na2CO3 +2HCl 2NaCl +H2CO3 FeCl3 + 3NaOH Fe(OH)3 + 3NaCl b. CO2 + 4H2 CH4 + 2H2O c. Odour + Some reactions are accompanied by a pungent smell or foul odour. For example, when ferrous sulphide is mixed with dilute acid, there is a smell of rotten eggs. 4. Uses of hydrogen In weather balloons.-. the use of these balloons has been stopped because of the in ammable nature of hydrogen. Nowadays, helium gas is used in weather balloons in place of hydrogen. This is due to the formation of hydrogen sulphide. In hydrogenation of oils -. Solid vanaspati is obtained by passing hydrogen gas through an oil in the presence of nickel as a catalyst. This process is called hydrogenation. Oil is a liquid because it is an unsaturated compound. On passing hydrogen, we get a saturated compound which is a solid and gives a better taste. FeS + 2HCl FeCl2 + H2S d. Formation of Precipitate BaCl2 + Na2SO4 BaSO4 + 2NaCl BaSO4 + 2NaCl e. Change of State - In many chemical reactions, a change of state is observed. For example, the reaction might start with solid or liquid reactants and end up with gaseous products and vice versa. The reaction between hydrogen sulphide and chlorine (both gases) produces sulphur (solid) and hydrogen chloride (gas). In the oxy-hydrogen ame. A mixture of hydrogen and oxygen, when used in a welding torch, burns, giving a temperature of 2800 3000 C. Such a ame is used in the cutting and welding of metals. As a fuel -. Liquid hydrogen, because of the high value of heat of combustion, is used as a rocket fuel. As a reducing agent.- Hydrogen gas is used as a reducing agent to obtain less reactive metals like copper, lead, tin, etc. from their oxides. However, hydrogen gas does not act as an e ective reducing agent when active metals are involved. H2S(g) + Cl2(g) 2HCl(g) + S(s) change of colour in a chemical reacti on I In the manufacture of chemicals.Many important compounds like hydrochloric acid, methanol and ammonia are manufactured using hydrogen as a reactant. 98 1. Copper carbonate-CuCO3 2. Change of colour in a chemical reaction. 3. This is an example of thermal decomposition and are endothermic reactions. 4. Calcium hydroxide reacts with carbon dioxide to form calcium carbonate and water. heat CuO(s) + CO2(g) 5. CuCO3(s) Ca(OH)2(s) + CO2(g) CaCO3(s) + H2O(g) Answers to Worksheets WORKSHEET 1 d. i. As a catalyst 1. a. Fullerene ii. As insulators b. In fullerene, the carbon atoms are held together in a cage like structure and the number of carbon atoms vary between 30 and 900. Also these carbon atoms exist as unlinked particles. e. Buckminster fullerene (C60) 2. Ethane C2H 6 Glucose C6H12O6 3. Solid lime, dolomite c. On heating at 1000 C, the cage-like structure of fullerenes collapses. Liquid petrol, grease Gaseous natural gas, marsh gas. WORKSHEET 2 Carbon 1. Amorphous Crystalline Diamond Graphite Fullerenes Soot Charcoal Coal Coke Gas Carbon 2. a. Carbon monoxide b. 2C + O2 2CO c. It leads to death. 3. CO2, nitrous oxide, ozone, chloro uorocarbon, methane 4. CO2 is used in re extinguishers as it is not a supporter of combustion. 5. The process of heating organic substances in the absence of air is known as destructive distillation. a. Charcoal is formed as a residue. b. CO2, CO, CH4 and H2 gas are formed. 99 Model Test Paper 2 Time: 3 hours Total marks: 50 Section A A. Fill in the blanks. [5] 1. Endothermic reactions produce _______________ effect by absorbing heat. 2. Bosch s process is used in the preparation of _______________ . 3. Oxy-hydrogen ame is used in the _______________ and _______________ of metals. 4. A simple solution of sugar in water is an example of _______________ . 5. CO2 is a _______________ gas which turns _______________ litmus _______________ . B. Multiple choice questions. [5] 1. Food grains can be stored in an atmosphere of ________ to protect them from insects. a. CO b. CO2 c. CH4 d. Na2CO3 c. Helium d. Sodium c. Rutherford d. Niels Bohr c. 1 d. Variable 2. An element that does not have a neutron. a. Carbon atom b. Hydrogen atom 3. The nucleus was discovered by a. Chadwick b. Dalton 4. The valency of all inert gases is a. 1 b. 0 5. Heating of copper carbonate gives a black solid known as a. CuCO2 b. CuO c. CO d. CuCO4 C. State True or False. [5] 1. When ferrous sulphide is mixed with dilute acid, it gives a pleasant odour. 2. Galena is a sulphide ore. 3. Metals are arranged in the increasing order of their reactivity in the metal activity series. 4. The rate of formation of a solution can be increased by stirring. 5. Carbon has 6 protons and 6 neutrons. D. Name the following. [4] 1. An allotrope of carbon which does not have a de nite form 2. An opaque mixture of a liquid and insoluble solid 3. Gas that burns in air with a pop sound 4. Substance that removes oxygen or provides an electron to an atom Section B A. De ne the following. [3] 1. Water of crystallization 2. Haber Bosch Process 100 3. Decomposition reaction B. Short answer questions. [12] 1. Differentiate between a. Single displacement reaction and double displacement reaction b. Saturated and Unsaturated solution 2. Why does sky appears blue in colour? 3. What is Sabatier Process? Write a balanced equation involved in this process. C. Long answer questions. [12] 1. Study the diagram. a. What does it show? b. Write the chemical equation involved in the above process. c. Why is the gas formed collected by the upward displacement of air? d. Is the gas formed acidic or basic? 2. Write the balanced equation for the following and the name of the gas evolved. a. Mg reacts with steam b. Cu reacts with cold water c. Ca reacts with cold water d. Mg with hot water 3. What is dissolution ? Explain the dissolution of sugar and salt in water. 4. Write the uses of carbon dioxide 101 Answers to Model Test Paper 1 Section A condensation is a process by which a substance changes from the gaseous state to the liquid state on cooling. A 1. Law of conservation of mass 2. Catalyst 2. For rusting, both oxygen and water are essential. When oxygen and water present in the atmosphere come in contact with the iron, it rusts. Painting of iron gate does not allow the oxygen and moisture present in the atmosphere to come in contact with the iron and prevents it from rusting. 3. reactants; products 4. Re ning 5. Motion; collide B 1. (a) 2. (a) 3. (b) 4. (b) 5. (d) C 1. True 2. False 4. True 5. False 3. 3. True 4. 1. Anode 2. Chemical equation 3. Condensation 4. Alloy Section B A. 1. A suspension is a heterogeneous mixture containing solid particles that are suf ciently large for sedimentation. 2. The arrangement of electrons in various energy levels around the nucleus of the atom of an element is called electronic con guration. 3. Catalyst is a chemical substance that increases or decreases the speed of a reaction. A catalyst can be positive or negative. For example, iron is used as a catalyst in the preparation of NH3. B. 1. a. The substance that chemically reacts in a chemical reaction are known as reactants whereas the new substances formed in a reaction are called products N2 + 3H2 (a) Write the symbols side by side Ca OH (b) Write the valencies below each +2 1 (c) Interchange the valencies and write as subscripts Ca (OH)2 (d) Ratio of valencies in the lowest terms 1 : 2 (e) Chemical formula of calcium chloride (OH)2 C 1. Materials required for this are - mixture of kerosene oil and water or CCl4 (carbon tetrachloride) and water, separating funnel . Pour the mixture of kerosene oil and water in a separating funnel. Keep it undisturbed till two separate layers of oil and water are visible. Open the stopcock of the separating funnel and pour the lower layer into a beaker carefully. Close the stopcock immediately as the other layer reaches near the stopcock. Thus ,we conclude that one of the liquids is left in the separating funnel and the other is obtained in the beaker. 2NH3 N2 and H2 are reactants NH3 is a product b. Freezing is the process by which a substance changes from the liquid state to the solid state on cooling, whereas 102 2. Electrostatic bond is formed by the sharing of electrons to attain stability . The oppositely charged ions formed are held together by a strong electrostatic force, which is called the ionic bond. In sodium atom, its L shell has 8 electrons and the valence shell M has 1 electron. Hence, the sodium atom has to lose its 1 valence electron to become stable. When it comes in contact with one chlorine atom, with 7 electrons in its valence shell M, the chlorine atom accepts 1 electron from the sodium atom. As a result, the sodium atom forms a sodium cation (Na+) and one chlorine atom forms one chloride anion (Cl ). Due to the electrostatic force of attraction between the anion and cation, a new compound, sodium chloride (NaCl), is formed. 3. a. Bohr s atomic model 4. The balanced equation for the reaction becomes CaCO3 CaO + CO2 Mass of CaCO3 = Ca + C + (3 O) = 40 + 12 + 48 = 100 Mass of CaO = Ca + O = 40 + 16 = 56 Mass of CO2 = C + (2 x O) = 12 + 32 = 44 b. Electrons tend to occupy the lowest energy level available, which is known as the ground level. c. When an electron moves back to its ground state, the extra energy is emitted as radiation. d. The maximum number of electrons each shell can hold is 2n2 where n is the serial number of the shell. a. 100 gm of CaCO3 form 56 g of CaO 1 g of CaCO3 will form g of CaO 150 g of CaCO3 will form g = 84 g CaO b. 56 g of CaO is obtained when 100 gm of CaCO3 is heated 1 g of CaO is obtained from g of CaCO3 g CaO is obtained from = 300 g of CaCO3 is required. Answers to Model Test Paper 2 Section A of water which is necessary for certain salts to crystallise out from their aqueous solutions. This water makes it possible for them to form crystals, and it is responsible for the shapes of their crystals. A 1. Cooling 2. Hydrogen 3. Cutting; Welding. 2. Hydrogen combines with nitrogen in the ratio 3:1 by volume, in presence of catalyst iron and promoter molybdenum, at a pressure of 200 atmospheres and a temperature of 450 C, and gives ammonia. 4. True Solution. 5. Acidic; blue; red B 1. (b) 2. (b) 3. (c) 4. (b) 5. (b) C 1. False 2. True 4. True 5. True 3. False 200 atm Fe/Mo 2NH . N2 + 3H2 3 This process of manufacturing ammonia gas is known as the Haber Bosch process. D 1. Amorphous form 2. Suspension 3. When on heating, a compound breaks up into elements or simpler compounds, it is called the decomposition of the substance and such reactions are called decomposition reactions. For e.g. 3. Hydrogen 4. Reducing agent Section B A. 1. Water of crystallization is the xed amount 103 heat CaCO3 CaO + CO2(g) B 1. a. It is a reaction in which a more reactive element displaces a less reactive element from a compound and takes its place. This is also called a substitution reaction. For example, Fe(s) + CuSO4(aq) Cu(s) + FeSO4(aq) b. A solution in which no more solute can dissolve at a speci c temperature is called a saturated solution, whereas a solution in which more solute can dissolve at a speci c temperature is called an unsaturated solution. 2. The sky appears blue in colour due to the scattering of blue colour of the sun s light by colloidal particles, i.e., due to the Tyndall effect. 3. Hydrogen reacts with carbon dioxide at elevated temperatures (optimally 300 400 C) and pressures in the presence of a nickel catalyst to produce methane and water. CO2 + 4H2 CH4 + 2H2O + energy This reaction is called the Sabatier reaction or the Sabatier process. C 1. a. Laboratory set-up for the preparation of carbon dioxide b. CaCO3 + 2HCl CaCl2 + CO2 + H2O c. Carbon dioxide being heavier, displaces air upward and occupies the gas jar. d. CO2 is an acidic gas. It turns blue litmus red. 2. a. Mg reacts with Steam Mg(s) + H2O(g) MgO(s) + H2 b. No reaction c. Ca reacts with Cold water, vigorous reaction, oats over water. Ca(s) + 2H2O(l) Ca (OH)2(aq) + H2 d. Mg reacts with hot water, oats over water Mg(s) + 2H2O(hot) Mg(OH)2(s)+ H2 104 3. When a solid disappears in water, the solid is said to be dissolved and the product so obtained is called a solution, whereas the process involving the disappearance of a solid in water is called dissolution. Dissolution of sugar in water is a physical change, as no new substance is formed and the solution remains the same, retaining the properties of sugar as well as water. When we dissolve sugar in water, the molecules of sugar spread throughout the water, but they don t change their chemical identity. When a salt dissolves in water, the negative part of water attracts the positive part of the salt and the positive part of water attracts the negative part of the salt. As a result, the salt disappears. This phenomenon is called the dissolution of salt in water. The dissolution of salt is a chemical process, as it breaks down into sodium and chloride ions. This can be represented in the form of the equation given below. NaCl(s) Na + (aq) + Cl (aq) This solution can conduct electricity. So, we can say that dissolving a covalent compound like sugar does not result in a chemical reaction and, therefore, will undergo only a physical change. When we dissolve any ionic compound like salt in water, it undergoes a chemical change. 4. Soft drinks. Carbon dioxide is made to dissolve under pressure in soft drinks. Being acidic, it gives a tickling sensation to the tongue while drinking. In Industries. Carbon dioxide is used: (a) In the manufacture of washing soda and baking soda. (b) In the manufacture of urea a fertilizer. It is produced by heating a mixture of ammonia and carbon dioxide. In the medical eld. Oxygen mixed with 5% carbon dioxide called carbogen helps in treating gas poisoning, suffocation and shocks. In re extinguishers. A re extinguisher works on the principle that carbon dioxide is not a supporter of combustion.

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