Formatting page ...
Table of Contents Table of Contents CHAPTER 08: STUDY OF COMPOUNDS HYDROGEN CHLORIDE ..................... 1 Hydrogen Chloride: ........................................................................................................................... 1 Preparation of hydrogen chloride gas: ......................................................................................... 1 Physical Properties of Hydrogen Chloride Gas:........................................................................... 3 Chemical properties of Hydrogen Chloride Gas: ......................................................................... 4 Hydrochloric Acid: ............................................................................................................................. 4 Preparation of Hydrochloric Acid:................................................................................................. 4 Physical Properties of Hydrochloric Acid: .................................................................................... 5 Chemical properties of Hydrochloric Acid: ................................................................................... 5 Uses of hydrochloric Acid:............................................................................................................ 6 Tests for Hydrogen Chloride gas and Hydrochloric acid:.................................................................. 6 Tests for Chloride ion: .................................................................................................................. 7 PREVIOUS YEARS BOARD QUESTIONS: ........................................................................................................ 7 CLASS WORK EXERCISE: ............................................................................................................................ 8 HOME WORK EXERCISE: ............................................................................................................................. 9 ANSWERS: ................................................................................................................................................ 10 CHAPTER 09: STUDY OF COMPOUNDS AMMONIA ........................................ 14 Introduction: ..................................................................................................................................... 14 Occurrence: ..................................................................................................................................... 14 Preparation of Ammonia Gas: ......................................................................................................... 14 General methods: ....................................................................................................................... 14 Laboratory Preparation: ............................................................................................................. 15 Preparation of Aqueous Ammonia: ................................................................................................. 16 Manufacture of Ammonia (Haber Process): .................................................................................... 16 Physical properties of ammonia: ..................................................................................................... 17 Fountain Experiment: ................................................................................................................. 18 Chemical properties of ammonia: ................................................................................................... 18 Tests for ammonia gas and Ammonium ion:................................................................................... 20 Uses of ammonia: ........................................................................................................................... 21 PREVIOUS YEARS BOARD QUESTIONS: ...................................................................................................... 21 CLASS WORK EXERCISE: .......................................................................................................................... 22 HOME WORK EXERCISE: ........................................................................................................................... 23 ANSWERS: ................................................................................................................................................ 24 CHAPTER 10: STUDY OF COMPOUNDS NITRIC ACID .................................... 26 Introduction: ..................................................................................................................................... 26 Occurrence: ..................................................................................................................................... 26 Formation of nitric acid in atmosphere. ...................................................................................... 26 Laboratory Preparation:................................................................................................................... 27 Formation of nitric acid by Ostwald s process: (Industrial Preparation) ..................................... 27 Properties of Nitric acid: .................................................................................................................. 28 Uses of Nitric acid: .......................................................................................................................... 30 Test for nitric acid and nitrates: .................................................................................................. 30 PREVIOUS YEARS BOARD QUESTIONS: ...................................................................................................... 31 CLASS WORK EXERCISE: .......................................................................................................................... 33 HOME WORK EXERCISE: ........................................................................................................................... 34 ANSWERS: ................................................................................................................................................ 34 Volume 2 of 2 Universal Tutorials X ICSE Chemistry CHAPTER 11: STUDY OF COMPOUNDS SULPHURIC ACID ........................... 36 Introduction: ..................................................................................................................................... 36 Occurrence: ..................................................................................................................................... 36 Preparation of Sulphuric Acid: ......................................................................................................... 36 Manufacture of Sulphuric Acid (Contact Process): ......................................................................... 37 Properties of Sulphuric Acid: ........................................................................................................... 39 Uses of Sulphuric Acid: ................................................................................................................... 40 PREVIOUS YEARS BOARD QUESTIONS: ...................................................................................................... 41 CLASS WORK EXERCISE: .......................................................................................................................... 43 HOME WORK EXERCISE: ........................................................................................................................... 45 ANSWERS.................................................................................................................................................. 45 CHAPTER 12: ORGANIC CHEMISTRY ................................................................. 47 12A: ORGANIC COMPOUNDS: .................................................................................................................... 47 Introduction: ..................................................................................................................................... 47 Organic Compounds: ...................................................................................................................... 48 Sources of organic compounds:................................................................................................. 48 Unique Nature of Carbon Atoms: .................................................................................................... 48 Tetravalency of the carbon atom:............................................................................................... 48 Catenation: ................................................................................................................................. 49 Isomerism: .................................................................................................................................. 49 Functional Group: ............................................................................................................................ 49 Hydrocarbons: ................................................................................................................................. 50 Classification of Hydrocarbons:.................................................................................................. 50 Comparison of Saturated and Unsaturated Hydrocarbons: ....................................................... 50 Alkyl Group: ..................................................................................................................................... 51 Structure and Isomers: .................................................................................................................... 51 Structure: .................................................................................................................................... 51 Isomers:...................................................................................................................................... 52 Homologous series:......................................................................................................................... 52 Examples of Homologous Series: .............................................................................................. 53 Characteristics of a homologous series: .................................................................................... 53 Nomenclature: ................................................................................................................................. 53 IUPAC names:............................................................................................................................ 56 Writing Structural Formula From IUPAC name: ......................................................................... 57 12B ALKANES: ......................................................................................................................................... 58 Homologous series of alkanes: .................................................................................................. 58 Methane and Ethane: ................................................................................................................. 60 Chemical properties: .................................................................................................................. 62 Uses: .......................................................................................................................................... 63 12C ALKENES: ......................................................................................................................................... 63 Preparation of ethene (ethylene):............................................................................................... 64 Properties of Alkenes: ................................................................................................................ 65 Reaction with ozone (ozonolysis):.............................................................................................. 66 Polymerization: ........................................................................................................................... 66 Oxidation: ................................................................................................................................... 66 Combustion of ethene: ............................................................................................................... 66 Uses of ethene: .......................................................................................................................... 67 12D ALKYNES: ......................................................................................................................................... 67 Ethyne (Acetylene): .................................................................................................................... 67 Chemical properties: .................................................................................................................. 69 12E ALCOHOLS: ....................................................................................................................................... 70 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Table of Contents Laboratory preparation: .............................................................................................................. 71 Industrial method (large scale method): ..................................................................................... 71 Properties of alcohols: ................................................................................................................ 71 12F CARBOXYLIC ACIDS: .......................................................................................................................... 73 Carboxylic Acids: ........................................................................................................................ 73 Acetic acid CH3 COOH:.............................................................................................................. 74 Lab preparation: ......................................................................................................................... 74 Manufacture: .............................................................................................................................. 74 Physical properties: .................................................................................................................... 74 Chemical properties: .................................................................................................................. 75 Acetic acid is used: .................................................................................................................... 75 PREVIOUS YEARS BOARD QUESTIONS: ...................................................................................................... 76 CLASS WORK EXERCISE: .......................................................................................................................... 79 HOME WORK EXERCISE: ........................................................................................................................... 83 ANSWERS: ................................................................................................................................................ 85 Volume 2 of 2 Universal Tutorials X ICSE Chemistry Chapter 08: Study of Compounds Hydrogen Chloride 1 Chapter 08: Study of Compounds Hydrogen Chloride Occurrence Hydrogen Chloride Gas Preparation Physical and Chemical Properties Hydrochloric Acid Preparation Physical and Chemical Properties Uses Test for Hydrogen Chloride Gas and Hydrochloric Acid Hydrogen Chloride: Molecular formula: HCl Molecular mass: 36.5 Bond: H Covalent H + Cl H Cl or H Cl Dot diagram or Lewis structure Cl Orbital diagram Occurrence: z HCl gas occurs in volcanic emissions. z HCl acid is present in gastric juice of mammals. Preparation of hydrogen chloride gas: General Preparation: z By synthesis (Direct combination): Moist hydrogen gas combines with chlorine in the presence of diffused sunlight. Hydrogen + Chlorine Hydrogen chloride H2(g) + Cl2(g) 2HCl(g) Diffused Sunlight z By heating metallic chloride with conc. sulphuric acid: Metal chloride + Sulphuric acid [conc.] Salt + Hydrogen chloride Laboratory Preparation: z In the laboratory, hydrogen chloride gas can be prepared by the action of concentrated sulphuric acid on sodium chloride. Reactants: Volume 2 of 2 Sodium chloride and concentrated sulphuric acid. Universal Tutorials X ICSE Chemistry 1 2 Procedure: Place some common salt in a flat bottomed flask and pour concentrated sulphuric acid through the thistle funnel. On heating the mixture gently, HCl gas is evolved. The gas is dried by passing through concentrated sulphuric acid. It is collected by upward displacement of air. Conc. Sulphuric Acid Dry Hydrogen chloride NaCl + H2SO4 con. Conc. H2SO4 Air Air Heat Preparation of hydrogen chloride gas from common salt Reaction: < 200o C NaCl + H2SO4 NaHSO4 + HCl Though it is a reversible reaction, yet it goes to completion as hydrogen chloride continuously escapes as a gas. The reaction can occur upto the stage of formation of sodium sulphate on heating above 200 C. above 200o C NaHSO4 + NaCl Na2SO4 + HCl i) Sodium chloride is cheap and therefore it is preferred for preparation of HCl over other metal chlorides. ii) Conc. nitric acid is not used during the preparation of HCl because it is volatile and may volatilize out alongwith hydrogen chloride. Purification of HCl gas: z It is dried by passing through conc. sulphuric acid. The other drying agents like phosphorus pentoxide (P2O5) and quick lime (CaO) cannot be used, since they react with hydrogen chloride as follows. 2P2O5 + 3HCl POCl3 + 3HPO3 CaO + 2HCl CaCl2 + H2O Collection: z z Hydrogen chloride gas is collected by the upward displacement of air as it is 1.28 times heavier than air. It is not collected over water, since it is highly soluble in water. Identification: z z 2 When the jar is completely filled with hydrogen chloride, fumes appear above the jar s mouth. When hydrogen chloride gas is exposed to air it gives white fumes, due to the formation of hydrochloric acid on reacting with atmospheric water vapour. Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 08: Study of Compounds Hydrogen Chloride z z 3 In order to know whether the gas jar is full, bring a rod dipped in ammonium hydroxide near its mouth. HCl + NH4OH NH4Cl + H2O Dense white fumes of ammonium chloride will be produced proving thereby that the jar is full of hydrogen chloride gas. Precautions: z The lower end of the thistle funnel must be dipped in conc. sulphuric acid. Delivery tube should be dipped in drying agent i.e. conc. H2SO4. z Temperature is maintained at nearly 200 C z At higher temperature i.e. above 200 C: The apparatus which is made of glass may crack. Fuel is wasted. Sodium sulphate formed, forms a hard crust which sticks to the glass and is difficult to remove. Physical Properties of Hydrogen Chloride Gas: 1. Colour colourless gas 2. Smell pungent smell 3. Taste acidic taste (sour) 4. Physiological nature It is corrosive in nature. It irritates nose, throat and lungs. 5. Density It is about one and a quarter times heavier than air (V.D. of HCl is 18.25 and that of air 14.4). 6. Boiling point 83 C 7. Melting point 113 C 8. Liquefaction and solidification When subjected to a high pressure (40 atm.) at low temperature (10 C), it is liquefied to a colourless liquid. 9. Solubility Hydrogen chloride gas is highly soluble in water (1 volume of water dissolves 452 volumes of the gas at room temperature). HCl being covalent is soluble in organic non polar solvents such as acetone and toluene. Experiment: To show that HCl gas is heavier than air. Air It can be proved by pouring the gas in a jar with a burning candle. The candle gets extinguished because HCl gas being heavier occupies the lower portion of the jar and forces the air out of it. HCl gas Experiment: Volume 2 of 2 To show that HCl gas is highly soluble. The great solubility of the gas can be demonstrated by means of Fountain Experiment as illustrated below. Universal Tutorials X ICSE Chemistry 3 4 Fou untain Exp periment: z z Take a dry round bot ttomed flask k filled with dry d HCl gas. Arrange A the apparatus as a shown in the t fig. On the mouth of o the flask, fix a rubb ber stopper with w two holes s. Through one o hole pass sa long jet tube, t and th hrough other hole pass s a dropper with w few drop ps of water. Put P the jet tube in the bea aker containin ng blue litmu us solution. Press the e dropper. It is i seen that the blue litm mus solution enters e the je et tube with a great forc ce, forming a red fountain n. HC Cl Gas Je et Tube Blue Fountain D Dropper Red d Litmus Solu ution R Reason: As the e water goes s in the flask k from the dr ropper, HCl gas g present in the flask dissolves due to o its high so olubility, ther reby lowering g the pressu ure inside. T The outside pressure being higher h pushe es the blue litmus solution inside, thro ough the jet t tube. The blue litmus solution turns red r due to the acidic natu ure of hydrog gen chloride gas. g Chem mical prop perties of f Hydroge en Chloride Gas: C Combustibil lity: The gas is neither combustible e nor a supp porter of com mbustion. It does not b burn, and ext tinguishes a burning splin nt. Thermal T diss sociation: On O heating above 500 , it t dissociates into hydroge en and chlorine. > 500 C H2 + Cl2 2HCl W With metals s: All active metals that come before e hydrogen in the electr rochemical series s like s sodium, pota assium, calc cium, magne esium, zinc, iron etc. form their cor rresponding chlorides w when heated d and liberate e hydrogen. With W ammon nia: It combines with amm monia to form m dense white fumes of a ammonium chloride. c NH3(g) + HCl(g) NH N 4Cl(s) Hydr rochloric c Acid: Whe en hydrogen chloride gas s is dissolved d in water, hy ydrochloric acid a is formed d. The e covalent compound ioni izes in water r due to its po olar nature. HCl + H2O H3O+ + Cl Prepa aration of f Hydroch hloric Acid: Lab boratory method: m z Hydrochlo oric acid is pr repared by dissolving d hyd drogen chlor ride gas in w water. z The gas is passed in nto water unt til no more gas g is absor rbed, the pro oduct is concentrated ains about 36 6% of hydrog gen chloride by mass. and conta Pro ocedure: z z 4 An invert ted funnel, connected to the Hyd drogen Chloride gas g supply, is i placed in the t beaker in n such a way that it just tou uches the water w taken in the trough. Since HC Cl gas is hig ghly soluble in water the e water rises s up in the funnel, back suction occurs an nd in turn the e level outsid de the funne el falls creating an air ga ap between the t rim of U Universal Tuto orials X ICS SE Chemistr ry Volu ume 2 of 2 Chapter 08: Study of Compounds Hydrogen Chloride z 5 the funnel and the surface of water. The pressure outside and inside then becomes equal and the water which had risen in the funnel falls down again. This process continues till the water in the trough is saturated with hydrogen chloride gas resulting in the formation of hydrochloric acid. The funnel arrangement: Prevents or minimizes back-suction of water. Provides a large surface area for absorption of HCl gas. Why is funnel arrangement used? z Hydrogen chloride gas is sufficiently soluble, so, it is absorbed in water more quickly than it is being generated in the flask. z In this case, the pressure in the delivery tube and flask is reduced and the atmospheric pressure from outside forces the water back upto the delivery tube. This effect is called back suction . HCl acid forms constant boiling mixture at 110 C: z z A dilute aqueous solution of hydrochloric acid gets gradually concentrated on distillation, till the concentration of the acid reaches 22.2% HCl by weight and 77.8% water by weight which boils at 110 C. When this concentration is reached, no further increase in concentration of the acid is possible by boiling. A constant boiling mixture is a solution which boils without any change in its composition. Physical Properties of Hydrochloric Acid: 1. 2. 3. 4. 5. Colour Smell Taste Physiological action Solubility colourless Pungent choking smell acidic Concentrated acid is corrosive and causes blisters on the skin. Readily soluble in water in all proportions. Chemical properties of Hydrochloric Acid: Nature: Aqueous solution is strongly acidic, and shows all properties of acids. Action on metals: Hydrochloric acid reacts with metals above hydrogen in the activity series forming metallic chlorides and evolving hydrogen. Ca + 2HCl CaCl2 + H2 Action on oxides and hydroxides: It reacts with oxides and hydroxides (bases) to form salt and water only. MgO + 2HCl MgCl2 + H2O With salts of weaker acids: It decomposes salts of weaker acids eg. carbonates, bicarbonates, sulphites and sulphides. CaCO3 + 2HCl CaCl2 + H2O + CO2 ; NaHCO3 + HCl NaCl + H2O + CO2 ; Ca(HCO3)2 + 2HCl CaCl2 + 2H2O + 2CO2 ; Na2SO3 + 2HCl 2NaCl + H2O + SO2 ; Na2S + 2HCl 2NaCl + H2S Action on thiosulphates: Dilute hydrochloric acid reacts with thiosulphates to produce sulphur dioxide gas and yellow sulphur is precipitated. Na2S2O3 + 2HCl 2NaCl + H2O + SO2 + S Volume 2 of 2 Universal Tutorials X ICSE Chemistry 5 6 Action on metallic nitrites: On warming with metallic nitrites, dilute hydrochloric acid gives metallic chlorides and oxides of nitrogen. 2KNO2 + 2HCl 2KCl + 2HNO2; 2HNO2 H2O + NO + NO2 Reaction with nitrates: Dil. HCl does not normally react with nitrates. However on reaction with silver nitrate solution it gives a thick curdy white precipitate of silver chloride. AgNO3 + HCl AgCl + HNO3 The white precipitate is insoluble in nitric acid but soluble in ammonium hydroxide solution, and forms a complex salt called diammine silver (I) chloride is formed. AgCl + 2NH4OH [Ag(NH3)2]+Cl + 2H2O When exposed to light, silver (I) chloride blackens since it decomposes into chlorine and black powder of Ag. 2AgCl 2Ag + Cl2 Similarly, lead nitrate and mercury (I) nitrate react with hydrochloric acid to give white precipitate of lead and mercury (I) chloride. Pb (NO3)2 + 2HCl PbCl2 + 2HNO3 Hg2 (NO3)2 + 2HCl Hg2Cl2 + 2HNO3 Uses of hydrochloric Acid: General uses: z In the laboratory as a reagent and for preparation of aqua regia. Industrial uses: z In the manufacture of Chlorine and chlorides e.g. ammonium chloride used in dry cells. Dyes, drugs, paints and photographic chemicals (silver chloride). Glucose from starch. z In industry to pickle steel, as HCl dissolves the oxides. Steel before being plated with tin or chromium has to be purified by pickling in HCl and some inhibitors. z For purifying bone black, because HCl dissolves the calcium phosphate present in bones. z To remove rust from iron sheets. z For cleaning metal surfaces before painting, electroplating, galvanizing, soldering etc. z In the extraction of glue from bones. In tanning and calico printing industry. Medicine: Dil. HCl is prescribed to patients with decreased activity of their gastric juices. HCl acid helps in the digestion of proteins and also in destroying microorganisms that enter the alimentary canal alongwith the food. Tests for Hydrogen Chloride gas and Hydrochloric acid: HCl gas possesses a characteristic irritating smell. HCl gas gives thick white fumes of ammonium chloride, when a glass rod dipped in ammonia solution is held near the vapours of the acid. NH3 + HCl NH4Cl With silver nitrate solution, both the gas and the acid give a white precipitate of silver chloride. AgNO3 + HCl AgCl + HNO3 The precipitate is insoluble in nitric acid but soluble in ammonium hydroxide. A greenish-yellow gas i.e. chlorine, is liberated when concentrated hydrochloric acid is heated with oxidizing agent like manganese dioxide. The gas liberated turns starch iodide paper blue black. 6 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 08: Study of Compounds Hydrogen Chloride 7 Tests for Chloride ion: If concentrated sulphuric acid is added to the salt, white pungent fumes of hydrogen chloride gas are evolved. NaCl + H2SO4 NaHSO4 + HCl If the salt is warmed with manganese dioxide and concentrated sulphuric acid, chlorine gas is evolved which bleaches moist litmus paper. 2NaCl + 2H2SO4 + MnO2 Na2SO4 + MnSO4 + 2H2O + Cl2 If silver nitrate solution is added to a solution of the salt containing chloride, a white curdy precipitate is formed. Cl (aq) + AgNO3 AgCl + NO3 The precipitate is soluble in ammonium hydroxide but insoluble in nitric acid. PREVIOUS YEARS BOARD QUESTIONS: Year 2012: 1) Identify the anion present in the compounds, When a solution of compound Y is treated with silver nitrate solution a white precipitate is obtained which is soluble in excess of ammonium hydroxide solution. 2) State one chemical test between each of the following pairs: i) Sodium carbonate and sodium sulphite. ii) Manganese dioxide and Copper (II) oxide. 3) Refer to the flow chart diagram below and give balance equations with conditions, if any, for the following conversions A to D. Iron (II) B Sodium Chloride A Hydrogen Chloride Chloride C D Ammonium Chloride Lead Chloride Year 2010: 1) The diagram shows an apparatus for the laboratory preparation of hydrogen chloride. [5] i) Identify A and B. ii) Write the equation for the reaction. iii) How would you check whether or not the gas jar is filled with hydrogen chloride? iv) What does the method of collection tell you about the density of hydrogen chloride? Year 2008: 1) What property of hydrogen chloride is demonstrated when it is collected by downward delivery (upward displacement)? [1] 2) Why is hydrogen chloride not collected over water? [1] 3) Write the equations for the following reactions: [2] i) Dilute hydrochloric acid and sodium thiosulphate. ii) Dilute hydrochloric acid and lead nitrate solution. Year 2007: 1) Write balanced chemical equations for the reaction of dilute Hydrochloric acid with each of the following: [5] i) Iron ii) Sodium hydrogen carbonate iii) Iron ( ) sulphide iv) Sodium sulphite v) Sodium thiosulphate solution Volume 2 of 2 Universal Tutorials X ICSE Chemistry 7 8 Year 200 06: 1) Write balanced d chemical equation for th he reaction of o zinc and dilute hydroch hloric acid. [1] 2) What do you observe [1] o when n hydrochloric acid is add ded to silver nitrate soluti ion? 05: Year 200 1) Write balance ed equation for the follo owing reaction: Mangan nese(IV) oxid de and concentrated [1] Hy ydrochloric acid. a 2) i) Name the experiment e illustrated abo ove. ii) Which prop perty of hydrogen chlori ide is demonstrated by this experim ment? iii) State the colour c of the water that has entered the round[3] bottomed flask. CLASS WORK EXE ERCISE: 1) Dr raw a labeled d diagram for the laborato ory preparation of hydrog gen chloride gas. 2) Write the react tions betwee en common salt s and conc centrated sulphuric acid: i) below 200 C and ii) at 200 C 3) Na ame the dryin ng agents: i) Used in dry ying hydrogen chloride ga as. ii) Which cann not be used to t dry hydrog gen chloride gas? 4) Ca alcium oxide and phosph horus pentox xide are good drying age ents but they y are not em mployed to dry y hydrogen chloride c gas. Give reason ns for each. 5) Ex xplain why: i) Anhydrous HCl is a po oor conducto or while aq. HCl H is an exc cellent condu uctor. ii) Only a ve ery dilute solu ution of hydr rogen chlorid de in water can c be conce entrated by boiling b the solution while w a very concentrated c d solution would become less concent trated when boiled. iii) When the e stopper of a bottle full of o hydrogen chloride gas s is opened there are fum mes in the air. iv) ) A solution n of hydrogen n chloride in water turns blue litmus red, r and cond ducts electric city, while a solution of the same e gas in tolue ene: a) has no effect on litm b) does mus and d not con nduct electric city v) Hydrogen n chloride gas s does not co onduct electricity. ) Hydrochlo oric acid cond ducts electric c current. vi) vii) Hydrogen n chloride gas s dissolve in toluene but this solution does not co onduct electri icity. viii) White thic ck fumes are e formed whe en a glass ro od dipped in NH N 4OH is br rought near the t mouth of a bottle e full of HCl gas. g ix) ) Dry hydro ogen chloride e gas does not n affect a dry d strip of bl lue litmus pa aper but it turns red in the presence of a drop p of water. x) Hydrogen n chloride gas s is not collected over wa ater. 6) Write the main n difference in n hydrogen chloride c gas and hydroch hloric acid. 7) De escribe brief fly the meth hod employe ed to dissolve hydrogen n chloride g gas in water r as it is pre epared in the e laboratory. 8) What is the pu urpose of using a funnel while prepa aring hydroch hloric acid fro om hydrogen n chloride ga as? 9) i) Name one element whi ich reacts with hydrogen n to form a compound c wh hich is strongly acidic in water. ii) Explain why y dilute hydro ochloric acid d cannot be concentrated c d by boiling b beyond 22.2% %. 8 U Universal Tuto orials X ICS SE Chemistr ry Volu ume 2 of 2 Chapter 08: Study of Compounds Hydrogen Chloride 9 10) i) With reference to given figure for the dissolution of hydrogen chloride gas in water, explain briefly, how the device with the mouth of the funnel just below the surface of water prevents the back suction of water? HCl Air gas ii) How does solubility of hydrogen chloride gas gap in water change with temperature? Water 11) Describe an experiment, giving the arrangement of the apparatus you would use, to prove the extreme solubility of hydrogen chloride gas. 12) i) Name two gases which chemically combine to form: (a) a solid (b) a liquid. ii) Name the chemical in which gold can be dissolved. 13) Give reasons for the following: i) An aqueous solution of HCl is acidic in nature. ii) Silver nitrate solution can be used to distinguish HCl from HNO3. 14) Which one of the following metals will not liberate hydrogen gas from hydrochloric acid? [Na, Cu, Fe, Mg] 15) State what you observe when silver nitrate solution is added to dilute hydrochloric acid. 16) What do you see when conc. hydrochloric acid is added to lead (IV) oxide with warming. 17) What must be added to sodium chloride to obtain hydrogen chloride? 18) What would you see when hydrogen chloride mixes with ammonia? 19) Hydrogen chloride dissolves in water forming an acidic solution. i) Name the experiment which demonstrates that hydrogen chloride is very soluble in water. ii) Give three distinct tests [apart from using an indicator] you would carry out with this solution to illustrate the typical properties of an acid. 20) Name the gas produced with exposure of chlorine water to sunlight. HOME WORK EXERCISE: 1) Write equation for the reactions of aqueous hydrochloric acid on: i) Silver nitrate solution ii) magnesium foil iii) caustic soda solution iv) iron wire v) zinc carbonate vi) copper oxide vii) lead nitrate solution 2) By what experiment can it be proved that HCl contains hydrogen and chlorine? Write equations for the reactions. i) Name all the products formed when conc. hydrochloric acid is warmed with manganese dioxide. ii) Name one metallic oxide which reacts with hydrochloric acid to give a coloured solution. iii) Name two colourless gases, which when mixed produce a white solid. 3) Complete the following reaction and balance them, < 200 C i) NaCl + H2SO4 > 200 C ii) NaCl + H2SO4 iv) NaHSO3 + HCl iii) NH4OH + HCl vi) Pb3O4 + HCl v) Cu(NO3)2 + HCl 4) How will the action of dilute hydrochloric acid on sodium carbonate and sodium sulphite enable you to distinguish between these two compounds? 5) Write the equation for the reaction of hydrochloric acid with each of the following: i) Lead nitrate solution ii) Manganese (IV) oxide. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 9 10 6) Write the balanced equations for the following reactions of: i) Dilute hydrochloric acid and sodium sulphite. ii) The preparation of hydrogen chloride from sodium chloride and sulphuric acid. State whether the sulphuric acid should be concentrated or dilute. iii) The reaction of hydrogen chloride with ammonia. 7) State how you would prove that HCl contains i) Hydrogen using an active metal below Mg ii) Chlorine using an oxidizing agent containing lead ANSWERS: Class Work Exercise: Conc. Sulphuric Acid 1) Dry Hydrogen chloride NaCl + H2SO4 con. Conc. H2SO4 Air Air Heat Preparation of hydrogen chloride gas from common salt < 200 C > 200 C 2) i) NaCl + H2SO4 NaHSO4 + HCl ii) NaHSO4 + NaCl Na2SO4 + HCl 3) i) It is dried by passing it through conc. sulphuric acid. ii) P2O5 and quick lime, CaO cannot be used to dry HCl. 4) The other drying agents like phosphorus pentoxide, P2O5 and quick lime, CaO cannot be used, since they react with hydrogen chloride. 2P2O5 + 3HCl POCl3 + 3HPO3 CaO + 2HCl CaCl2 + H2O 5) i) When hydrogen chloride gas is dissolved in water, hydrochloric acid is formed. The covalent compound ionizes in water due to its polar nature. HCl + H2O H3O+ + Cl Thus aqueous HCl is a good conductor. Dry hydrogen chloride gas or liquid hydrogen chloride does not conduct electricity, as it has only molecules and no ions. It shows covalent nature of hydrogen chloride. ii) A dilute aqueous solution of hydrochloric acid gets gradually concentrated on distillation, till the concentration of the acid reaches 20.2% HCl by weight and 77.8% water by weight which boils at 110 C. When this concentration is reached, no further increase in concentration of the acid is possible by boiling A very dilute solution of HCl becomes concentrated by boiling but a concentrated solution of HCl becomes dilute on boiling. Reason: Vapours evolved in the first case consist mostly vapours of water but when concentrated HCl is boiled its vapours consist molecules HCl. iii) When the jar is completely filled with hydrogen chloride, fumes appear above the jar s mouth. These fumes consist of hydrochloric acid which is formed by combination of HCl with moisture (H2O) contained in the air. iv) When hydrogen chloride gas is dissolved in water, hydrochloric acid is formed. The covalent compound ionizes in water due to its polar nature. HCl + H2O H3O+ + Cl 10 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 08: Study of Compounds Hydrogen Chloride 11 These ions conduct electricity. Dry hydrogen chloride gas or liquid hydrogen chloride does not turn dry blue litmus paper, showing non acidic character of the gas. Further, liquefied hydrogen chloride does not conduct electricity, as it contains only molecules. It shows covalent nature of hydrogen chloride. v) Dry HCl gas or liquid hydrogen chloride does not conduct electricity as it is covalent in nature. Covalent compounds do not conduct electricity. vi) Hydrochloric acid conducts electric current because hydrogen chloride gas when dissolved in water forms hydrochloric acid. This covalent compound ionises in water due to its polar nature. HCl + H2O H3O+ + Cl . Thus on ionization the H+ and Cl ions conduct electric current. vii) The gas is also soluble in dry toluene, but in that case it neither turns blue litmus red nor conducts electricity. This indicates the absence of H+ in toluene showing thereby that hydrogen chloride is a covalent compound. When hydrogen chloride gas is exposed to air, it gives white fumes due to the formation of hydrochloric acid on reacting with atmospheric water vapour. viii) In order to know whether the gas jar is full, bring a rod dipped in ammonium hydroxide near its mouth. Dense white fumes of ammonium chloride will be produced proving thereby that the jar is full of hydrogen chloride gas. ix) Dry hydrogen chloride does not ionize to give H+ and Cl ions. Since Cl ions are not released blue litmus paper is not affected by Cl ions. But when a drop of water is added to HCl gas it dissolves in the water and ionizes as follows HCl + H2O H3O+ + Cl . The Cl ions now turn blue litmus red. x) It is not collected over water, since it is highly soluble in water. 6) Hydrogen chloride gas no effect on blue litmus paper HCl gas does not ionize to release Cl ions Hydrochloric acid turns blue litmus red HCl acid ionizes in water releasing Cl ions (HCl + H2O H3O+ + Cl ) which turn blue litmus paper red. 7) Hydrochloric acid is prepared by dissolving hydrogen chloride gas in water by means of an inverted funnel arrangement. The gas is passed into water until no more gas is absorbed, the product is concentrated and contains about 36% by mass of hydrogen chloride. Procedure: The rim of the funnel is placed such that it just touches the water taken in a trough. Back suction occurs, the water rises up in the funnel and in turn the level outside the funnel falls creating an air gap between the rim of the funnel and the surface of water. The pressure outside and inside then equalizes and the water which had risen in the funnel falls down again. This process continues till the water in the trough is saturated with hydrogen chloride gas resulting in formation of hydrochloric acid. 8) The funnel arrangement: a) prevents or minimizes back suction of water. b) provides a large surface area for absorption of HCl gas. 9) i) Chlorine ii) A dilute aqueous solution of hydrochloric acid gets gradually concentrated on distillation, till the concentration of the acid reaches 20.2% HCl by weight and 77.8% water by weight which boils at 110 C. When this concentration is reached, no further increase in concentration of the acid is possible by boiling. A very dilute solution of HCl becomes concentrated by boiling but a concentrated solution of HCl becomes dilute on boiling. Reason: Vapours evolved in the first case consist mostly vapours of water but when concentrated HCl is boiled its vapours consist molecules HCl. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 11 12 10) i) The rim of the funnel is placed such that it just touches the water taken in a trough. Back suction occurs, the water rises up in the funnel and in turn the level outside the funnel falls creating an air gap between the rim of the funnel HCl Air and the surface of water. The pressure outside and gas gap inside then equalizes and the water which had risen in the funnel falls down again. This process Water continues till the water in the trough is saturated with hydrogen chloride gas resulting in formation of hydrochloric acid. ii) It increases with increase in temperature. 11) The great solubility of the gas can be demonstrated by means of the Fountain experiment. Take a dry round bottomed flask filled with dry HCl gas. On the mouth of the flask, fix a rubber stopper with two holes. Through, one whole pass a long jet tube and through other hole pass a dropper with few drops of water. Put the jet tube in the beaker containing blue litmus solution. Press the dropper. The blue litmus solution enters the jet tube with a great force, forming a red fountain. Reason: As the water goes in the flask from the dropper, HCl gas present in the flask dissolves due to its high solubility, thereby lowering the pressure inside. The outside pressure being higher pushes the blue litmus solution inside through the jet tube. 12) i) a) NH3(g) + HCl(g) NH4Cl (white solid) b) 2H2 + O2 2H2O (liquid) ii) Aqua Regia 13) i) HCl gas in solution gives HCl acid. This acid ionizes as follows, HCl + H2O H3O+ + Cl . The liberated H3O+ ion turns blue litmus paper red showing its acidic nature. But dry HCl gas does not ionize, so there is no effect on the dry litmus paper. ii) When AgNO3 is formed along with HNO3. This white ppt of AgCl does not dissolve in HNO3. AgNO3 + HCl AgCl + HNO3 (white curdy ppt) This white ppt of AgCl is soluble in NH4OH to form a complex diammine silver chloride. AgCl + NH4OH [Ag(NH3)3]+Cl + 2H2O 14) Cu 15) When AgNO3 is added to HCl (acid) a white curdy ppt of silver chloride is formed along with nitric acid. This white ppt is insoluble in HNO3. AgNO3 + HCl AgCl + HNO3. 16) Pb3O4 + 8HCl 3PbCl2 + 4H2O + Cl2 < 200 C NaHSO4 + HCl 17) NaCl + H2SO4 (conc.) 18) HCl(g) + NH3(g) NH4Cl(s) dense white fumes of solid NH4Cl. 19) i) Fountain experiment. ii) a) First test: HCl when it reacts with metals above hydrogen on the reactivity series forming metallic chlorides evolving hydrogen. (b) Second test: HCl reacts with a base to give salt and water, HCl + NaOH NaCl + H2O. (c) Third test: HCl reacts with metallic sulphides to give salt and hydrogen sulphide. HCl + Na2S NaCl + H2S 20) HCl Home Work Exercise: ii) Mg + 2HCl MgCl2 + H2 1) i) AgNO3 + HCl AgCl + HNO3 iv) Fe + 2HCl FeCl2 + H2 iii) NaOH + 2HCl NaCl + H2O vi) CuO + 2HCl CuCl2 + H2O v) ZnCO3 + 2HCl ZnCl2 + H2O + CO2 vii) Pb(NO3)2 + 2HCl PbCl2 2HNO3 12 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 08: Study of Compounds Hydrogen Chloride 13 2) i) MnO2 + 4HCl MnCl2 + 2H2O + Cl2 ii) FeO + 2HCl FeCl2 (green) + H2O iii) HCl(g) + NH3(g) NH4Cl (white solid) < 200 C 3) i) NaCl + H2SO4 NaHSO4 + HCl > 200 C Na2SO4 + HCl ii) NaCl + H2SO4 iii) NH4OH + HCl NH4Cl + H2O iv) NaHSO3 + HCl NaCl + H2O + SO2 v) Cu(NO3)2 + 2HCl CuCl2 + 2HNO3 vi) Pb3O4 + 8HCl 3PbCl2 + 4H2O + Cl2 4) Na2CO3 + 2HCl 2NaCl + H2O + CO2 NaHSO3 + HCl NaCl + H2O + SO2 From the products formed; Na2CO3 and NaHSO3 can thus be differentiated from each other 5) i) Pb(NO3)2 + 2HCl PbCl2 + 2HNO3 ii) MnO2 + 4HCl MnCl2 + 2H2O + Cl2 6) i) ii) iii) 7) i) HCl (dil.) + NaHSO3 NaCl + H2O + SO2 2NaCl + H2SO4 (conc.) Na2SO4 + 2HCl HCl(g) + NH3(g) NH4Cl(s) (white cloud of NH4Cl solid) Zn + 2HCl(g) ZnCl2 + H2 ii) PbO2 + 4HCl PbCl2 + 2H2O + Cl2 3PbCl2 + 4H2O + Cl2 Pb3O4 + 8HCl Volume 2 of 2 Universal Tutorials X ICSE Chemistry 13 14 Chapter 09: Study of Compounds Ammonia Introduction Occurrence Preparation of Ammonia gas General method of preparation Laboratory preparation Industrial preparation Preparation of Aqueous NH3 Physical and chemical properties of NH3 Uses of NH3 Tests for NH3 gas and NH + 4 ion Introduction: LONE PAIR Molecular formula of ammonia : NH3 Relative molecular mass: 17 LONE PAIR H H N N H H H H Lewis diagram or dot diagram Covalent bonding in ammonia Occurrence: Free state: Ammonia is present in small amounts in air and in traces in natural water. Combined state: In nature, ammonia occurs in combined form in many compounds such as ammonium chloride ammonium sulphate etc. Ammonium compounds do not occur as minerals as they are highly soluble in water. Forms of ammonia: Ammonia is used commonly in the following forms: Gaseous ammonia. Liquid ammonia Liquor ammonia fortis (880 NH3) saturated solution of NH3 0.880 sp. gravity. Laboratory bench reagent: It is a diluted solution of liquor ammonia. Preparation of Ammonia Gas: General methods: Ammonia gas can be prepared by warming an ammonium salt with caustic alkali, such as slaked lime or caustic soda or caustic potash. 14 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 09: 0 Study of Compounds C Ammonia 15 2NH4Cl(s) CaCl2(s) + 2H2O + 2NH3 ) + Ca(OH)2(s s) Laboratory Pr reparation n: Fro om ammon nium chlo oride: z Reactants: Ammoniu um chloride (NH4Cl) and d calcium hydroxide e [Ca(OH)2] in n the ratio of f 2 : 3 by weight. z Reaction: 2NH4Cl + Ca(OH) C C 2 + 2H2O + 2NH3 2 CaCl z Procedur re: Reactant ts are finely ground g and taken t in a round-bot ttomed flask fitted in a sla anting positio on, mouth downward ds. On heating the mixt ture, ammon nia gas is evolved. z Precautio ons: The flas sk is tilted in such a way that the wate er formed in the reaction does not trickle bac ck into the he eated flask and a thus brea aks it. z Drying of f ammonia gas: g In orde er to get dry ammonia, th he gas is pas ssed through h a drying tower con ntaining lump ps of quick lim me (CaO). z Collection: Ammonia a gas is collec cted in inverted gas jars by the down nward displac cement of air becaus se it is: z Lighter r than air (V.D. of NH3, 8.5, that of air r, 14.4). Extremely y soluble in water w and the erefore, it cannot be colle ected over water. U Unsuitability y of other dr rying agents s: Other drying agen nts like conc c. sulphuric acid, a phosph horous pento oxide and anhydrous a calcium m chloride ar re not used, as ammonia a being basic c reacts with t them. 2NH3 + H2 SO4 (NH4)2SO4 6NH3 + P2O5 + 3H2O 2 (NH4)3PO4 Ammo onium phosphate e CaCl2 + 4NH3 CaCl C 2. 4NH3 Note: : 1) Ra atio of reacta ants taken is s 2:3 by weig ght, higher ra atio by weigh ht of the alka ali may counteract the los ss by sublima ation of NH4Cl. 2) Ca alcium hydro oxide is used, , as it is chea ap and not deliquescent d like other alk kalies. 3) Th hough all am mmonium sal lts, on heatin ng with alkali lies give NH3, yet NH4NO O3 is not use ed as it is ex xplosive in na ature and it decomposes d forming nitro ous oxide an nd water vapo our. Fro om metal nitrides: n z Ammonia can also be e obtained by b the action n of water on nitrides of f metals. (T This method d is costly) z Reaction: 6 2O 3Ca a(OH)2 + 2NH H3 Ca3N2 + 6H Mg3N2 + 6H 6 2O 3Mg g(OH)2 + 2NH H3 AIN + 3H2O AI(OH)3 + NH3 Volume 2 of 2 U Universal Tuto orials X ICS SE Chemistr ry 15 16 z z Procedur re: Magnesiu um nitride or r Aluminum nitride n is kep pt in a round d bottomed fl lask fitted with a this stle funnel an nd a delivery y tube. Warm m water is add ded very slow wly. Ammonia gas is liber rated and magnesium hy ydroxide is also a formed but it remains in the flask and the liberated ammonia gas escapes through th he delivery tu ube. The ga as can be dried by passing p it thro ough quick li ime packed in i a drying to ower. Preparation of o Aqueo ous Amm monia: An aqueous so olution of am mmonia is prepared p by y dissolving amm monia in water. Since th he solubility is very high h, therefore, back suction of water w is poss sible. o the outer end of the To avoid this, a funnel is attached to deliv very tube with a rubber tubing (the process p is si imilar to the method used to change HCl gas into hyd drochloric acid). Procedure: Wa ater is taken n in a conta ainer and only a small port tion of the mouth of th he funnel is s dipped in water. As amm monia dissolv ves in water r at a higher rate than its s production in th he flask, the e pressure in n the funnel above wate er level decreases for a moment, and a water rush hes into the funnel. f As a result, the rim of the fun nnel loses its s contact with water. Sinc ce ammonia produced pu ushes the wate er down the funnel come es in contact with water again. a In this way, ammonia dissolves s in water with hout back suc ction of wate er. Manu ufacture of Ammonia (Ha aber Proc cess): Rea actants: Nitro ogen and hy ydrogen in the e ratio of 1:3 3 by volume. Sou urces of re eactants: z z z Nitrogen gas is obtained by fract tional distillation of liquid air. a Hydrogen n gas: is obtained fr rom water gas (Bosch pr rocess) or fro om natural ga as. Reacti ion: N2 + 3H H2 l 2NH3 + heat h The reac ction is re eversible, exothermic e and proceeds with a decre ease in volum me. Fav vourable conditions c s: z z z z Temperat ture: Optimu um temp. is 450 500 4 C Pressure e: Above 200 0 atm. Catalyst: Finely divide ed iron. Promoter r: Traces of molybdenum m m or Al2O3. Rat te of conv version: z 8% to 12% % of the reac cting gases get g converted d to ammonia a. Rec covery of ammonia a: z 16 Ammonia is separated d from the un nreacted nitro ogen and hy ydrogen by: Liquefa action, as am mmonia compared to N2 and a H2 is easily liquefiab ble. Absorb bing in wate er because NH N 3 is highly y soluble in water, while e N2 and H2 are very slightly y soluble. U Universal Tuto orials X ICS SE Chemistr ry Volu ume 2 of 2 Chapter 09: Study of Compounds Ammonia 17 Note: Since the reaction is exothermic, the heat evolved further maintains the temperature. External heating is therefore not required after the reactants are initially heated. z z Process: Nitrogen and hydrogen are dried, purified and then mixed in the ratio of 1: 3 respectively at a relatively high pressure. This mixture is passed in an electrically heated catalytic chamber containing finely divided iron with aluminium oxide or a little amount of molybdenum at a temperature of 500 C. Mixture of ammonia formed along with residual nitrogen and hydrogen exchanges their heat with the incoming unreacted nitrogen and hydrogen mixture. Catalyst Poison: The presence of carbon dioxide, carbon monoxide and traces of sulphur compounds (H2S) poisons the catalyst. The removal of these catalytic poisons from nitrogen and hydrogen is very essential. The hot mixture of the outgoing gases contains nearly 10% ammonia. The mixture is passed through the cooling pipes (condenser). Ammonia liquefies first whereas nitrogen and hydrogen do not liquefy easily. The unchanged nitrogen and hydrogen are re-circulated through the plant to get more ammonia. The reaction is exothermic, hence low temperature will favour the synthesis. However, at low temperature, the reaction proceeds slowly. In practice, the optimum temperature has been found to be in the range of 450 C to 500 C. Four volumes of reactants produce two volumes of product, hence high pressure favours the formation of ammonia. The optimum pressure is found to be 200 to 900 atm. Practically, a pressure of about 250 atm. is used. Catalyst and promoter: The speed of the reaction can be improved by using a catalyst which is finely divided iron, obtained by the reduction of iron oxide. Flow chart of Haber s Process: Dry nitrogen 1 Vol Compression Pump Dry hydrogen 3 Vol More than 200 atm. Pressure Electrically heated catalytic Chamber Condenser with cooling Pipes Liquid ammonia Uncombined N2 and H2 recycled back Fe/Mo N2 + 3H2 l 2NH3 + heat 450 C 500 C above 200 atm. A promoter is used to increase the efficiency of the catalyst, which is molybdenum or Al2O3. Physical properties of ammonia: Colour: Colourless. Odour: Strong, pungent choking smell. Taste: Slightly alkaline taste. Physiological action: Non-poisonous. If inhaled affects the respiratory system and brings tears to eyes. It is a powerful heart stimulant and may cause death when inhaled in large quantities. Density: Vapour density = 8.5 (Lighter than air) Nature: Alkaline nature Liquefaction: Easily liquefied at 10 C by compressing it at 6 atm. pressure. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 17 18 Boiling point: Liquid ammonia boils at 33.5 C. Freezing point: Solid NH3 melts at 77.7 C. Solubility: Highly soluble in water. 1 vol. of water dissolves about 702 vols. of ammonia at 20 C and 1 atm. pressure. Fountain Experiment: To demonstrate the high solubility of ammonia gas in water. Apparatus: z A round bottomed flask filled with ammonia gas. Ammonia Gas z Mouth of the flask is fitted with a rubber stopper with two holes, one for jet tube and the other for a dropper containing water. Jet Tube z A trough containing red litmus solution. z A retort stand to fix the round bottomed flask in inverted position as shown in. Blue Fountain Dropper Red Litmus Solution Procedure: z The dropper containing water is squeezed. z As few drops of water enter the flask, ammonia gas present in the flask gets dissolved in water, due to its high solubility. This creates a partial vacuum in the flask. z Since outside pressure is higher, the red litmus solution rushes up through the jet tube and emerges as a blue fountain. (Ammonia gas being basic, changes red litmus solution blue) z A bottle of liquor ammonia should be opened very carefully, only after cooling it in ice or cold water. There is high pressure inside the bottle of ammonia and on cooling, the pressure drops. This prevents sudden flushing out of the gas. z Liquid NH3 is NH3 gas which is kept under high pressure and very low temperature. Hence it is stored in gas cylinders under pressure. Chemical properties of ammonia: Thermal dissociation: z Ammonia gas dissociates into nitrogen and hydrogen at high temperature or by electric sparks. 2NH3 l N2 + 3H2 Basic properties: z z H Dry ammonia is a covalent molecule. So, it is neutral even in | liquefied form. Lone pair : N H | Its aqueous solution it is a very weak base, the basicity is due to H lone pair of electrons on its nitrogen atom. z An aqueous solution of ammonia [NH4OH] is a weak base. It dissociates partially to give hydroxyl ions. Hence conduct electricity. z The alkaline behavior is due to the hydroxyl ions [OH ] NH3 + H2O NH4OH; 18 NH4OH NH+ 4 + OH Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 09: Study of Compounds Ammonia 19 Reaction with acids: z z Ammonia being a weak base accepts protons [hydrogen ions] to form ammonium ions. It, therefore, reacts with acids to form ammonium salts. NH3 (gas) + HCl (gas) NH4Cl (solid); NH3 (gas) + HNO3 NH4NO3; 2NH3 (gas) + H2SO4 (NH4)2SO4 Reaction with soluble metal salts: z z Ammonium hydroxide reacts with soluble salts of metals to give insoluble precipitates of the respective metallic hydroxides. The pale blue precipitate of copper hydroxide dissolves in excess of ammonium hydroxide forming [tetraammine copper [II] sulphate] an azure blue (deep blue) soluble complex salt. FeSO4 + 2NH4OH (NH4)2SO4 + Fe(OH)2 FeCl3 + 3NH4OH 3NH4Cl + Fe(OH)3 Pb(NO3)2 + 2NH4OH 2NH4NO3 + Pb(OH)2 Zn(NO3)2 + 2NH4OH 2NH4NO3 + Zn(OH)2 CuSO4 + 2NH4OH (NH4)2SO4 + *Cu(OH)2 + (NH4)2SO4 + 2NH4OH Cu(OH)2 Copper hydroxide Ammonium sulphate [Cu(NH3)4]SO4 + 4H2O Ammonium hydroxide Tetraammine copper[II] excess sulphate Reaction with oxygen: z z Ammonia is not a supporter of combustion. It extinguishes a burning splint and does not burn in air. It burns in oxygen with yellow flame. Experiment: The burning of ammonia in oxygen. Reaction: 4NH3 + 3O2 2N2 + 6H2O Procedure: Dry Ammonia Gas Oxygen A wide glass tube is fitted with a cork carrying two tubes, one of which reaches just near the top and the other remains lower. Ammonia is passed through the longer tube, and oxygen through the shorter tube and a lighted is applied. Observation: Ammonia burns with a yellow flame and produces water vapours and nitrogen. It shows that ammonia contains nitrogen and hydrogen. The reaction is irreversible and strongly exothermic. Catalytic oxidation of ammonia: z In the presence of platinum at 800 C, ammonia reacts with oxygen to give nitric oxide and water vapour. Procedure: Pass dry ammonia gas and oxygen gas through inlets over heated platinum placed in the combustion tube, which in the heated state emits a reddish glow. Reaction: Pt ,800o C 4NH3 + 5O2 6H2O + 4NO + Heat Volume 2 of 2 Universal Tutorials X ICSE Chemistry 19 20 2NO + O2 2NO2 (brown gas) Observations: Reddish brown vapours of nitrogen dioxide [NO2] are seen in the flask due to the oxidation of nitric oxide [NO]. 2NO + O2 2NO2 The platinum [catalyst] continues to glow even after the heating is discontinued since the catalytic oxidation of ammonia is an exothermic reaction. Reaction with carbon dioxide: z Ammonia reacts with carbon dioxide at 150 and 150 atm. pressure to give urea which is a valuable nitrogenous fertilizer. 2NH3 + CO2 NH2CONH2 + H2O urea Ammonia as a reducing agent: Reduction of chlorine to hydrogen chloride: When chlorine reacts with ammonia, it is reduced to HCl forming NH4Cl which further combines with excess of ammonia. (a) When ammonia is in excess, 2NH3 + 3Cl N2 + 6HCl 6NH3 + 6HCl 6NH4Cl 8NH3 + 3Cl2 N2 + 6NH4Cl (excess) Observation: The yellowish-green colour of chlorine disappears and white fumes of ammonium chloride are formed. (b) When chlorine is in excess, Then the products are hydrogen chloride and yellow coloured highly explosive liquid nitrogen trichloride. NH3 + 3Cl2 3HCl + NCl3 Reaction of metallic oxides: Ammonia reduces heated metallic oxide to give metals and nitrogen. 2NH3 + 3CuO 3Cu + 3H2O + N2 Tests for ammonia gas and Ammonium ion: All ammonium salts generally produce ammonia gas when alkali like sodium hydroxide is added to them. Ammonia gas can easily be recognized by the following characteristics: It has a sharp characteristic odour. It turns moist red litmus blue, moist turmeric paper brown and phenolphthalein solution pink. It gives dense white fumes with conc. hydrochloric acid. NH3 + HCl NH4Cl It first forms a blue precipitate with copper sulphate solution and then dissolves it to form a deep blue coloured solution on addition of excess of ammonia solution. Ammonium salt gives light to deep brown colour or precipitate with Nessler s solution K2HgI4 (a solution of potassium mercuric iodide, made slightly alkaline with sodium hydroxide) 20 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 09: Study of Compounds Ammonia 21 Uses of ammonia: Ammonia is used in the manufacture of: Nitric acid by the Ostwald process. Nitrogenous fertilizers like ammonium sulphate, diammonium hydrogen phosphate, ammonium nitrate and urea. Explosives like ammonium nitrate. Other ammonium salts such as ammonium carbonate (used as smelling salt for reviving a fainted person), ammonium chloride used in dry cells and in the preparation of nitrogen gas. NaNO2(aq) + NH4Cl(aq) NaCl(aq) + NH4NO2(aq) NH4NO2(aq) N2(g) + 2H2O(g) Nylon and rayon, and sodium cyanamide, plastics, dyes, organic chemicals, explosives and wood pulp. Sodium carbonate by Solvay process. This process involves the interaction of ammonia, carbon dioxide, and sodium chloride in water solution resulting in the precipitation of sodium hydrogen carbonate. NaCl + NH3 + CO2 + H2O NaHCO3 + NH4Cl z The sodium hydrogen carbonate is separated and ignited to obtain sodium carbonate. 2NaHCO3 Na2CO3 + H2O + CO2 Liquid ammonia is used as a refrigerant: Because ammonia takes a lot of energy to vaporize (5700 calories per mole at 33 C). This heat is taken from the surrounding bodies which are consequently cooled down. Aqueous NH3 is used: z To remove grease and perspiration stains from clothes because it emulsifies / dissolves fats, grease etc. and acts as clearing agent. z For cleaning tiles, windows etc. z Ammonia is used as an important laboratory reagent in qualitative analysis. z Ammonia is used as a source of hydrogen. Liquid hydrogen is not safe to transport in cylinders. Hence, hydrogen is converted into ammonia which can be transported. At the destination, it is split into nitrogen and hydrogen by heated catalysts. Nitric acid by Ostwald process. z PREVIOUS YEARS BOARD QUESTIONS: Year 2012: 1) The following questions are based on the preparation of ammonia gas in the laboratory: i) Explain why ammonium nitrate is not used in the preparation of ammonia. ii) Name the compound normally used as a drying agent during the process. iii) How is ammonia gas collected? iv) Explain why it is not collected over water. Year 2010: 1) The diagram shows a simple arrangement of the fountain experiment: i) Name the two gases you have studied which can be used in this experiment. ii) What is the common property demonstrated by this experiment? Volume 2 of 2 Universal Tutorials X ICSE Chemistry [3] 21 22 CLASS WORK EXERCISE: 1) What is the formula of liquid ammonia? Account for the basic nature of this compound. 2) How is high solubility of ammonia demonstrated? How is ammonia collected in the laboratory? 3) Name a drying agent for ammonia. Why other drying agents like H2SO4, P2O5 and CaCl2 are not used? 4) Name: i) The gas which is prepared by Haber s process. ii) Two gases which give dense white fumes with ammonia. iii) One salt of ammonia in each case which is used in: a) Dry cell b) explosives c) medicine iv) An acidic gas which reacts with a basic gas liberating a neutral gas. v) A metallic chloride soluble in ammonium hydroxide. vi) The gas obtained when ammonia burns in an atmosphere of oxygen without any catalyst. vii) A nitride of a divalent metal which reacts with warm water liberating ammonia. viii) An amphoteric oxide reduced by the basic gas. ix) A white salt produced by an acid gas and a basic gas. 5) A substance A was heated with slaked lime and a gas B with a pungent smell is obtained Name the substances A and B and give the balanced equation. 6) A gas P gives dense white fumes with chlorine. Its aqueous solution gives a blue colour with copper i) Name the gas P ii) Give its formula iii) Give three uses of P 7) How do you prove that NH3 contains nitrogen and hydrogen? 8) Distinguish between liquor ammonia fortis and liquid ammonia. 9) Give reasons for the following: i) Liquid ammonia is used as a refrigerant in ice plants. ii) Aqueous solution of ammonia is used for removing grease stains from woollen clothes. iii) Aqueous solution of ammonia gives a pungent smell. iv) Aqueous solution of ammonia conducts electricity. v) Ammonia cannot be collected over water. 10) Give a chemical test to distinguish between the following: i) Ammonium chloride and sodium chloride ii) Ferric salt and ferrous salt iii) Liquid ammonia and liquor ammonia fortis iv) Sodium sulphate and ammonium sulphate 11) Correct the following: i) A reddish brown precipitate is obtained when ammonium hydroxide is added to ferrous sulphate. ii) Liquid ammonia is a solution of NH3 iii) Finely divided platinum is used in Haber s process. iv) Conc. H2SO4 is a drying agent for NH3 12) Explain catalytic oxidation of ammonia. 13) Ammonia is manufactured by Haber s process. i) Under what conditions do the reactants combine to form ammonia? Give a balanced equation for the reaction. ii) In what ratio by volume, are the above gases used? iii) State one possible source of each reactant used in Haber s process. iv) What is the function of: (a) Finely divided iron (b) molybdenum in the above process? v) Mention two possible ways by which ammonia product is removed from unchanged gases. vi) Under what conditions do N2 and H2 combine to form NH3.State one large scale use of NH3 14) Name a chloride which is soluble in excess of ammonium hydroxide 22 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 09: Study of Compounds Ammonia 23 15) Pick the odd member from the list giving reasons [Ammonia, sulphur Dioxide, Hydrogen Chloride, Carbon Dioxide.] 16) State what will you observe when ammonium hydroxide solution is added to copper sulphate in excess. 17) Complete and balance the following equation: CuO (heat) + NH3 18) Explain why ammonia is evolved when water is added to magnesium nitride. 19) In Haber s process: i) Name the product and the catalyst used. ii) State the approximate temperature and pressure in the process. 20) When ammonium hydroxide is added to solution B, a pale blue precipitate is formed .this pale blue precipitate dissolves in excess ammonium hydroxide giving an inky blue solution. What is the cation [positive ion] present in solution B? What is the probable colour of solution B? 21) When an ammonium salt is warmed with sodium hydroxide solution, ammonium gas is evolved. State three ways in which you could identify this gas. 22) During the laboratory preparation, how is ammonia dried and collected? 23) What do you observe when ammonia gas is bubbled through red litmus solution. 24) State what you observe when a piece of moist red litmus paper is placed in a gas jar of ammonia. 25) Ammonium salts decompose on heating. What other property do ammonium salts have in common? 26) Is ammonia denser or less dense than air? What property of ammonia is demonstrated by the Fountain Experiment? Write the correctly balanced equation for the reaction between ammonia and sulphuric acid. 27) Choose the correct word or phrase from the brackets to complete the following sentences and write balanced equation for the same. i) Ammonium chloride is a soluble salt prepared by [precipitation, neutralization]. ii) When ammonium chloride is heated, it undergoes [thermal decomposition, dissociation] iii) Heating ammonium chloride with sodium hydroxide produces [ammonia, nitrogen] 28) State what you observe when: neutral litmus solution is added to an alkaline solution. 29) What are the products formed when ammonia is oxidized with copper oxide? HOME WORK EXERCISE: 1) Copy and complete the following equations. i) Mg3N2 + 6H2O ii) 2NH3 + 3CuO iii) 8NH3 + 3Cl2 iv) 4NH3 + 5O2 a) What property of ammonia is illustrated by equation (ii)? b) What important industrial process starts from equation (iv)? 2) How is NH4OH prepared? What do you observe when ammonium hydroxide is added to the aqueous solution of: i) FeSO4 ii) ZnSO4 iii) CuSO4 3) Give balanced equations for the following conversions: i) Ammonia to nitrogen using an acidic gas ii) Ammonia to brown gas iii) Ammonia to nitrogen trichloride iv) Ammonia solution to an amphoteric hydroxide v) A nitride of a trivalent metal to ammonia vi) Lead oxide to lead 4) Give two reactions to show reducing property of ammonia. 5) Write balanced equation of the reaction in the preparation of ammonia from ammonium chloride Give two large scale uses of ammonia. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 23 24 6) Write a balanced equation for the laboratory preparation of ammonia from ammonium chloride. 7) Write equation for the following: i) Burning of ammonia in oxygen. ii) In the catalytic oxidation of ammonia. What would you observe in (i)? Name the catalyst used in (ii). In the reaction (ii) the catalyst glows red hot, why? What is the name of the industrial process which starts with the reaction referred to in (ii)? a) How soluble is ammonia in water? b) Give two reasons to show that the solution of ammonia in water contains hydroxide ions? c) Name a simple method you would employ to prepare ammonium salts in your laboratory? 8) The following reactions are carried out: A: Nitrogen + metal compound X B: X + water ammonia + another compound C: Ammonia + metal oxide metal + water + N2 One metal that can be used for reaction A is magnesium i) Write the formula of the compound X formed. ii) Write the correctly balanced equation for reaction B where X is the compound formed. iii) What property of ammonia is demonstrated by reaction C? 9) Industrially, ammonia is obtained by direct combination between nitrogen and hydrogen. i) Write the correctly balanced equation for the direct combination of nitrogen with hydrogen ii) Which of the metals iron, platinum, copper catalyse this direct combination? iii) Is the formation of ammonia promoted by the use of high pressure or low pressure? 10) Name (formula is not acceptable) the gas produced in the following reaction: Warming ammonium sulphate with sodium hydroxide solution. 11) Write the equation for preparation of Ammonia from ammonium chloride and calcium hydroxide. 12) Write the equation for the action of heat on (i) Ammonium chloride and (ii) Ammonium nitrate. State whether each reaction is an example of thermal decomposition or thermal dissociation. 13) i) Write the equation for the formation of ammonia by the action of water on magnesium nitride. ii) How is ammonia collected? iii) Why is ammonia not collected over water? iv) Which compound is normally used as a drying agent for ammonia? ANSWERS: Home Work Exercise: 1) i) Mg3N2 + 6H2O 3Mg(OH)2 + 2NH3 ii) 2NH3 + 3CuO 3Cu + 3H2O + N2 Pt.800 C iii) 8NH3 + 3Cl2 N2 + 6HCl iv) 4NH3 + 5O2 6H2O + 4NO + heat a) Reduction property of ammonia is illustrated in equation (II) b) The Ostwald s process for the manufacture of HNO3 2) When NH3 gas is passed through water ammonia being highly soluble in water dissolves in water to ammonium hydroxide as per the following equation. NH3 + H2O NH4OH. i) FeSO4 + 2NH4OH (NH4)2SO4 + Fe(OH)2 dirty green insoluble ppt. ii) NH4OH + ZnSO4 (NH4)2SO4 + Zn(OH)2 white ppt gelations solution ppt. iii) NH4OH + CuSO4 (NH4)2SO4 + Cu(OH)2 pale blue soluble ppt. 3) i) 2NH3 + 3Cl2 (acidic gas) N2 + 6HCl Pt.800 C ii) 4NH3 + 5O2 6H2O + 4NO + heat; 2NO + O2 2NO2 (brown gas) iii) NH3 + 3Cl2 3HCl + NCl3 iv) Zn(NO3)2 + 2NH4OH 2NH4NO3 + Zn(OH)2 white gelation (soluble) 24 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 09: Study of Compounds Ammonia 25 v) AlN + 3H2O NH3 + Al(OH)3 vi) 3PbO + 2NH3 3Pb + 3H2O + N2 4) 2NH3 + 3CuO 3Cu + 3H2O + N2 2PbO + 2NH3 3Pb + 3H2O + N2 5) Ca(OH)2 + 2NH4Cl CaCl2 + 2NH3 + 2H2O i) On a large scale ammonia is used for the manufacture of fertilizers ii) Manufacture of HNO3 by Ostwald s process. 6) 2NH4Cl + Ca (OH)2 CaCl2 + 2H2O + 2NH3 iii) It forms a dense white cloud of NH4Cl when the fumes come in contact with HCl acid Pt. 800 C 7) i) 4NH3 + 5O2 6H2O + 4NO + heat; 2NO + O2 2NO2 (brown gas) ii) Reddish brown vapours of Nitrogen dioxide are seen in the flask, due to the oxidation of NO. i) ii) a) b) 2NO + O2 2NO2 (brown fumes) The catalyst used in Pt. The Pt. catalyst glows red hot as the oxidation (catalytic) of ammonia is an exothermic process Ostwalds process for the manufacture of HNO3. NH3 is highly soluble in water. Dry ammonia is neutral as it is a covalent compound however (a) when ammonia is passed through water it becomes basic in nature showing the presence if OH ions (b) since it undergoes partial dissociation in aqueous solution to give (OH ) ions in low concentrations. NH3 + H2O NH4OH; NH4OH l NH+ 4 + OH The aqueous solution of ammonia turns red litmus blue and phenolphthalein solution pink. c) NH3 being basic in nature when dissolved in water forms ammonium salts by reacting with acids by the method of neutralization thus respective. Ammonium salts can be prepared. 8) i) Mg3N2 ii) Mg3N2 + 6H2O 2NH3 + 3Mg(OH)2 iii) Reduction property of NH3 9) i) N2 + 3H2 2NH3 ii) Fe iii) Low pressure 10) [Ammonia] (NH4)2SO4 + 2NaOH Na2SO4 + 2H2O + NH3 ] 11) 2NH4Cl + Ca(OH)2 CaCl2 + 2H2O + 2NH3 heat 12) i) NH4Cl NH3 + HCl heat (NH4) NO3 N2O + 2H2O 13) i) ii) iii) iv) [thermal dissociation] [thermal dissociation] Mg3N2 + 6H2O 2NH3 + 3Mg(OH)2 NH3 is collected by the downward displacement of air. As NH3 gas is highly soluble in water it is not collected over water. CaO as it does not react with NH3. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 25 26 Chapter 10: Study of Compounds Nitric Acid Introduction Occurrence Preparation of HNO3 Laboratory Preparation Industrial Preparation Physical and chemical Properties of HNO3 Uses of HNO3 Nitrates Preparation of Nitrates General Properties of nitrates Effect of heat on Nitrates Tests for Nitric Acid and Nitrates Introduction: O Molecular formula: HNO3 H O N Relative molecular mass: 63 O This acid was formerly known as aqua fortis meaning strong water. It is so called because it dissolves silver metal which would not dissolve in other acids. It also attacks skin giving yellow stains. Occurrence: In Free State, nitric acid is found in rain water where it occurs in traces after lightning. In combined state, it is found in the form of metallic nitrates such as Chile saltpetre (NaNO3), nitre (KNO3) or calcium nitrate [Ca(NO3)2]. Formation of nitric acid in atmosphere. During lightning discharge the nitrogen present in the atmosphere reacts with the oxygen to form nitric oxide. N2 + O2 2NO The nitric oxide is further oxidized to nitrogen dioxide. 2NO + O2 2NO2 The nitrogen dioxide dissolves in atmospheric moisture and in the presence of oxygen of the air forms nitric acid in the Free State which is washed down by the rain. 4NO2 + 2H2O + O2 4HNO3 26 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 10: 1 Study of Compounds C Nitric Acid 27 Labo oratory Preparatio P on: Rea actants: It is s obtained by b distilling conc. sulphuric acid with h nitrates of potassium Nitrate KNO O3 (nitre) or r sodium Nitra ate NaNO3 (c chile saltpetr re). Procedure: A mixture of f equal pa arts, by we eight, of pota assium/sodiu um nitrate an nd concentra ated sulphuri ic acid is heated gently to o 180 200 C in a glass retort. Sulph huric acid is a non volatile acid and produces volatile v nitric acid on reac cting with pot tassium nitra ate or sodium m nitrate. Laboratory p preparation of nitric n acid < 200 o C R Reactions: KNO3 + H2SO S 4 KHSO4 + HNO3 <200 o C NaNO3 + H2SO4 NaHSO O4 + HNO3 C Collection: The va apours of nit tric acid are condensed to a light yellow liquid by chilling the e receiver with ru unning cold water. w Note: : Pure acid is i colourless s but the acid d obtained in n the labora atory is slight tly yellow. The Th yellow colou ur is due to dissolution d of f reddish bro own coloured d nitrogen di ioxide gas in n the acid. Th his gas is produ uced due to the t thermal decompositio d on of a portio on of nitric ac cid. 4HNO O3 2H2O + 4NO2 + O2 The e yellow colour c of th he acid is removed: z z If dry air or CO2 is bu ubbled throu ugh the yello ow acid, the latter turns colourless because b it drives out t NO2 from warm w acid wh hich is further r oxidized to nitric acid. Nitrogen gas dissolve es in water and thus the yellow col lour of the a acid is remo oved. The reaction is s the reverse e of the deco omposition of f nitric acid. Form mation of nitric n acid d by Ostw wald s pro ocess: (In ndustrial Preparat tion) T The process is explained in three step ps: z Oxidation of ammonia a into nitric ox xide in cataly ytic chamber r z Oxidation of nitric oxid de in oxidatio on chamber z Absorption of nitrogen n dioxide in water w Oxidation of ammonia a into nitric c oxide in n the cataly ytic chamber: z A mixture e of dry air (free from carbon dioxide and a dust particles) p an nd dry ammonia in the ratio of o 10 : 1 by volume, v is first com mpressed an nd then pass sed into the cat talytic cha amber con ntaining platinum gauze as catalyst at t about T results in the oxida ation of 800 C. This ammonia into nitrogen n monoxide. Pt O2 4N NO + 6H2O + Heat 4NH3 + 5O 800o C z The react tion is exothermic and th he heat evolved maintains m the e temperature e of the catalytic chamber. c Th he hot gases s are then passed through a heat exchanger wh here they are mixed d with air and d passed into o another coo oling chambe er called oxid dising chamb ber. Volume 2 of 2 U Universal Tuto orials X ICS SE Chemistr ry 27 28 Oxidation of nitric oxide in oxidation chamber: z In this chamber, nitric oxide combines with oxygen to form nitrogen dioxide at about 50 C. 50o C 2NO(g) + O2(g) NO2(g) Absorption of nitrogen dioxide in water. z z The nitrogen dioxide together with the remaining air (sometimes more air is added at this stage) is passed through the absorption tower (a steel tower filled with quartz stone packed in layers), from the top of which warm water trickles. The nitrogen dioxide and oxygen present in the air (atmosphere) react with water to form nitric acid. 4NO2(g) + 2H2O(l) + O2(g) 4HNO3(aq) The nitric acid obtained at the bottom of the tower is concentrated above 50%. The above acid on further distillation gives 68% nitric acid. This acid is concentrated nitric acid which is used in laboratories. Concentration of nitric acid: Nitric acid upto 98% (fuming nitric acid) is obtained by distilling 68% HNO3 over conc. sulphuric acid. Pure 100% nitric acid is obtained by strongly cooling the 98% acid, when colourless crystals of pure nitric acid get separated at 42 C. Flowchart for Ostwald s process Dry NH3 1 vol CATALYTIC CHAMBER 4NH3 + 5O2 Pt 700 C 800 C 4NO + 6H2O + Dry Air 10 vols (dust free) No Oxygen HEAT EXCHANGER Nitric acid OXIDATION CHAMBER 50 C 2NO + O2 2NO2 ABSORPTION TOWER 4NO2 + 2H2O + O2 4HNO3 Reactants: Pure dry ammonia (NH3) and dry air in the ratio 1:10 (by volume) Properties of Nitric acid: Physical properties: z z z z z z z z 28 Colour: It is a colourless liquid (98% concentration) is yellowish brown in colour. Odour: Suffocating smell. Taste: Acidic (sour taste). Nature: Hygroscopic and fumes in air. Hence, the bottle containing nitric acid should always be stoppered. Density: 1.54g/cm3 (98%) but the commercial nitric acid(68%) has lower density 1.42 g/cm3 Boiling point and melting point: It boils at 86 C and melts at 42 C. Solubility: Soluble in water in all proportions. Physiological action: Non poisonous. It has a corrosive action on the skin. Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 10: Study of Compounds Nitric Acid 29 Chemical Properties: z Stability: Pure nitric acid is rather unstable to heat or sunlight. It decomposes to give yellow solution due to the formation of nitrogen dioxide. 4NO2 + 2H2O + O2 4HNO3 Sunlight z Acidic properties: Nitric acid in water solution is a very strong monobasic acid. HNO3 ionises almost completely in dilute aqueous solution to produce hydrogen ions and nitrate ions. HNO3(aq) H+ + NO3 z It turns blue litmus red. Reaction with alkalis: It neutralises alkalies to form salt and water. Reaction with carbonates and bicarbonates: It reacts with carbonates and bicarbonates to give salt, water and carbon dioxide. CaCO3 + 2HNO3 Ca(NO3)2 + H2O + CO2 Action with metal oxides [Bases]: All metallic oxides react with dilute nitric acid to form their respective soluble metallic nitrates and water only. K2O + 2HNO3 2KNO3 + H2O Oxidising properties: Oxidising properties are due to nascent oxygen which it gives on decomposition. 2HNO3 (conc.) 2NO2 + H2O + [O] 2HNO3 (dil.) 2NO + H2O + 3[O] Action with metallic sulphites: Metallic sulphites from potassium sulphite to copper (II) sulphite in metal activity series, react with dilute nitric acid to form their soluble metallic nitrates, water and sulphur dioxide gas. K2SO3 + 2HNO3 2KNO3 + H2O + SO2(g) Action on non metals: Non metal+Acid Oxidised product+Water+ Nitrogen dioxide CO2 + 2H2O + 4NO2 C + 4HNO3 H2SO4 + 2H2O + 6NO2 S + 6HNO3 P4 + 20HNO3 4H3PO4 + 4H2O + 20NO2 Action on inorganic compounds Sulphur dioxide: 3SO2 + 2H2O + 2HNO3 3H2SO4 + 2NO Hydrogen sulphide: 3H2S + 2HNO3 3S + 2NO + 4H2O Potassium iodide: 2KI + 4HNO3 2KNO3 + I2 + 2NO2 + 2H2O Volume 2 of 2 Ferrous sulphate: 6FeSO4 + 3H2SO4 + 2HNO3 3Fe2(SO4)3 + 2NO + 4H2O Action on organic compounds Conc. nitric acid brings about oxidation of organic compounds. It oxidises organic compounds to carbon dioxide and water. [C6H10O5]n + Nitric acid Water + CO2 + NO2 Saw Dust [hot conc.] Action on metals Nitric acid reacts with all metals except gold and platinum. The action of nitric acid on metals depends on the temperature used and its concentration. Cold, dilute nitric acid oxidises metals to their nitrates and liberates nitric oxide. 3Cu + 8HNO3 3Cu(NO3)2 + 4H2O + 2NO Concentrated nitric acid [or hot dilute nitric acid] liberates nitrogen dioxide. Cu + 4HNO3 Cu(NO3)2 + 2H2O + 2NO2 Universal Tutorials X ICSE Chemistry 29 30 Very dilute acid reacts with very active metals such as magnesium and manganese at room temperature to give their nitrates and hydrogen gas. Mg + 2HNO3 Mg(NO3)2 + H2 (V. dilute) z Mn + 2HNO3 Mn(NO3)2 + H2 These reactions prove that nitric acid contains hydrogen. Metals like iron, aluminium, cobalt and nickel become passive (inert) when treated with pure concentrated nitric acid. It is due to the formation of extremely thin layer of insoluble metallic oxide which stops the reaction. Reaction as aqua regia: Conc. nitric acid (1 part by volume) when mixed with conc. hydrochloric acid (3 parts by volume) gives a mixture called aqua regia (meaning royal water). HNO3 + 3HCl NOCl + 2H2O+ 2[Cl] (Nitrosyl chloride) Action on proteins: Nitric acid produces yellow stains on proteins and proteinous substances such as skin, flesh, silk, feathers etc. The stains turn orange when treated with ammonia. The yellow colour is due to the formation of xanthoproteic acid. Uses of Nitric acid: To etch designs on copper and brassware. Reason: Nitric acid acts as a solvent for a large number of metals except noble metals. To purify gold. Reason: Gold may contain Cu, Ag, Zn, Pb etc. as impurities which dissolve in nitric acid. It acts as a rocket fuel oxidant. In preparation of fertilizers. Calcium nitrate Ca(NO3)2, Ammonium nitrate NH4NO3, Nitro chalk [NH4NO3 + CaCO3], Basic calcium nitrate CaO.Ca(NO3)2 In the preparation of aqua regia which dissolves noble metals. Industrial uses: In the manufacture of: Explosives Synthetic fibres like artificial silk, nylon, celluloid, plastics, rayon, photographic film etc. Important compounds like nitrates of potassium, ammonium, silver etc. Dyes/ Drugs/ Perfumes. Test for nitric acid and nitrates: On heating z Conc. nitric acid gives brown fumes. 4HNO3 2H2O + 4NO2 + O2 Brown fumes z Nitrates on heating produces reddish brown fumes of nitrogen dioxide [NO2] evolved. Metallic nitrate Metallic oxide + NO2 + O2 On adding Cu to HNO3 or acidified nitrates 30 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 10: Study of Compounds Nitric Acid z 31 Dense reddish brown fumes of nitrogen dioxide [NO2] evolved. Cu + 4HNO3 Cu(NO3)2 + 2H2O 2NO2 z Brown Ring Test Procedure: To the aqueous solution of a nitrate or nitric acid: Add freshly prepared saturated solution of iron [II] sulphate. Nitrate Now add conc. sulphuric acid carefully from the And iron (ii) sides of the test tube, so that it should not fall Sulphate Solution drop wise in the test tube. Cool the test tube in water. A brown ring appears at the junction of the two liquids. Reaction: 6FeSO4 + 3H2SO4 + 2HNO3 3Fe2(SO4)3 + 4H2SO4 + 2NO FeSO4 + NO FeSO4 . NO Concentrated Sulphuric Acid Brown Ring [Nitroso ferrous sulphate, a brown compound] PREVIOUS YEARS BOARD QUESTIONS: Year 2013: 1) Choose the most appropriate answer from the following options: Among the following compounds identify the compound that has all three bonds (ionic, covalent and coordinate bond). A) Ammonia B) Ammonium chloride C) Sodium hydroxide D) Calcium chloride Year 2012: 1) Some word/ words are missing in the following statements. You are required to rewrite the statements in the correct from using the appropriate word/words. i) Ethyl alcohol is dehydrated by sulphuric acid at a temperature of about 170 C. ii) Aqua regia contains one part by volume of nitric acid and three parts by volume of hydrochloric acid. iii) Magnesium nitride reacts with water to liberate ammonia. iv) Cations migrate during electrolysis. v) Magnesium reacts with nitric acid to the liberate hydrogen gas. Year 2008: 1) Select the correct answer from the choices A, B, C, D which are given Ammonia can be obtained by adding water to [1] A) Ammonium chloride B) Ammonium nitrite C) Magnesium nitride D) Magnesium nitrate 2) Identify the following substances: i) An alkaline gas (A) which gives dense white fumes with hydrogen chloride. ii) A dilute acid (B) which does not normally give hydrogen when reacted with metals but does give a gas when it reacts with copper. [2] 3) Write equations for the following reactions: i) Aluminium nitride and water ii) Dilute nitric acid and copper 4) Copy and complete the following table relating to important industrial processes. Output refers to the product of the process not the intermediate steps. Name of process Haber s Process ________ Inputs Hydrogen + ____ Ammonia + air Catalyst ________ ________ Equation for catalysed reaction _____ _________ Output ______ Nitric acid 5) What is the property of nitric acid which allows it to react with copper? Volume 2 of 2 Universal Tutorials X ICSE Chemistry 31 32 Year 2007: 1) a) i) Of the two gases, ammonia and hydrogen chloride, which is more dense? Name the method of collection of this gas. ii) Give one example of a reaction between the above two gases which produces a solid compound. b) Write a balanced equation for a reaction in which ammonia is oxidized by: i) a metal oxide, ii) a gas which is not oxygen. c) The figure given below illustrates the apparatus used in the laboratory preparation of nitric acid. i) Name A (a liquid), B (a solid) and C (a liquid). (Do not give the formulae) ii) Write an equation to show how nitric acid undergoes decomposition. iii) Write the equation for the reaction in which copper is oxidized by concentrated nitric acid. [1] 2) You enter a laboratory after a class has completed the Fountain experiment. How will you be able to tell whether the gas used in the experiment was hydrogen chloride or ammonia? Year 2006: 1) What do you observe when: i) nitric acid is kept in a reagent bottle for a long time? ii) excess of ammonia is passed through an aqueous solution of Lead nitrate? [2] 2) i) Explain why only all glass apparatus should be used for the preparation of nitric acid by heating concentrated sulphuric acid and potassium nitrate. ii) Write a chemical equation to illustrate the acidic nature of nitric acid. iii) Name the products formed when ammonium nitrate is heated. [3] 3) i) Name the substance used for drying ammonia. ii) Write an equation to illustrate the reducing nature of ammonia. iii) With reference to Haber s process for the preparation of ammonia, write the equation and the conditions required. [4] Year 2005: 1) Write balanced chemical equations for the following reactions: i) Sulphur and hot concentrated nitric acid ii) Sodium nitrate and concentrated sulphuric acid [2] 2) a) i) Dilute nitric acid is generally considered a typical acid except for its reaction with metals. In what way is dilute nitric acid different from other acids when it reacts with metals? ii) Write the equation for the reaction of dilute nitric acid with copper. iii) Account for the yellow colour that appears in concentrated nitric acid when it is left standing in an ordinary glass bottle. [3] b) i) Which feature of the ammonia molecules leads to the formation of ammonium ion when ammonia dissolves in water? ii) Name the other ion formed when ammonia dissolves in water. iii) Give one test that can be used to detect the presence of the ion produced in (b) (ii). [3] c) Write the equations for the following reactions which result in the formation of ammonia: i) A mixture of ammonium chloride and slaked lime is heated. ii) Aluminium nitride and water. [2] 32 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 10: Study of Compounds Nitric Acid 33 CLASS WORK EXERCISE: 1) What is (a) Aqua fortis (b) Aqua regia? 2) Conc. nitric acid prepared in laboratory is yellow in colour. Give reason. How is this colour removed? 3) Conc. nitric acid renders iron passive. Why? 4) Explain, why the following statements are not correct: a) The element nitrogen can be obtained in the pure state by removing CO2 and O2 from air. b) Ammonium salts, on heating, decompose to give ammonia. 5) Describe the manufacture of nitric acid by the catalytic oxidation of ammonia. 6) a) Name the catalyst which is used in the oxidation of ammonia to prepare nitric oxide. Name the other product of the oxidation reaction. b) A gas A reacts with another gas B in the presence of a catalyst to give a colourless gas C . The gas C when comes in contact with air produces a brown gas D . The solution of A in water turns red litmus blue. Explain the observations. 7) Nitric acid cannot be concentrated beyond 68% by the distillation of a dilute solution of HNO3. Explain why? 8) Name: a) a nitrate of metal which on heating does not give nitrogen dioxide. b) a nitrate which on heating leaves no residue behind. c) a metal nitrate which on heating is changed into metal oxide. d) a metal nitrate which on heating is changed into metal. 9) Mention three important uses of nitric acid. Give the property of nitric acid involved in the use. 10) Name the oxide of nitrogen which turns brown on exposure of air. How is it prepared? 11) Nitric acid is manufactured by Ostwald s process. a) Give the source of ammonia gas used in the manufacture. b) What is the ratio of ammonia and air taken in this process? c) Name the catalyst used in the process. d) Name the oxidizing agent used in this process. 12) Give reasons for the following: The apparatus for the preparation of nitric acid by heating concentrated sulphuric acid and potassium nitrate, should be all glass. 13) Write down the word equations or balanced equations for the following: a) action of concentrated nitric acid on copper b) action of heat on sodium nitrate 14) State the conditions for the oxidation of ammonia to nitrogen monoxide (nitric oxide) in the manufacture of nitric acid by Ostwald s process. Write the balanced equation of the reaction. 15) Give reasons for the following: a) Commercial concentrated nitric acid is yellow in colour, but when it is diluted with water, it turns colourless. Give one chemical test for nitric acid. b) In the laboratory preparation of nitric acid, the mixture of concentrated sulphuric acid and sodium nitrate should not be heated very strongly above 200 C. 16) The laboratory preparation of nitric acid from potassium nitrate. 17) State what you observe when: a) A piece of moist red litmus paper is placed in a gas jar of ammonia. b) Silver nitrate solution is added to dilute hydrochloric acid. 18) i) Potassium nitrate is prepared from potassium hydroxide and nitric acid. Name the type of this reaction. ii) Which gas is produced when potassium nitrate is heated? Write the equation for the reaction. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 33 34 HOME WORK EXERCISE: 1) Starting from lead nitrate, how can you obtain: (a) lead monoxide, (b) lead 2) During thunderstorm, rain water contains nitric acid. Explain with reactions. 3) Name the products formed when: a) carbon and conc. nitric acid are heated b) dil. HNO3 is added to copper. 4) a) Write balanced chemical equation for the preparation of nitric acid from potassium nitrate. b) In the preparation of nitric acid from KNO3 concentrated hydrochloric acid is not used in place of concentrated sulphuric acid. Explain why? 5) Give two chemical equations for each of the following: a) Reactions of nitric acid with non metals. b) Nitric acid showing acidic character. c) Reactions between nitric acid and inorganic compounds. d) Nitric acid acting as oxidizing agent. 6) Write the balanced equation for the following: a) Action of concentrated nitric acid on copper b) Action of heat on sodium nitrate c) Action of heat on ammonium nitrate d) Action of heat on AgNO3 7) How will you prepare the following from nitric acid? a) Sodium nitrate b) Copper nitrate c) Lead nitrate d) Magnesium nitrate e) Ferric nitrate f) Aqua regia 8) Describe all that you would observe when copper nitrate is heated. 9) a) write an equation for the following reaction: Action of heat on potassium nitrate. b) Name a nitrate which on heating gives oxygen as the gaseous product. 10) From the following list of substances, choose one substance in each case which matches the description given below: Ammonium nitrate, calcium hydrogen carbonate, copper carbonate, lead carbonate, potassium nitrate, sodium carbonate, sodium hydrogen carbonate, zinc carbonate. a) A nitrate which gives off only oxygen when heated. b) A nitrate which on heating decomposes into dinitrogen oxide (nitrous oxide) and steam. c) A nitrate which gives off oxygen and nitrogen dioxide when heated. 11) Write the equation for the reaction, dilute nitric acid producing carbon dioxide. ANSWERS: Home Work Exercise: 1) 2Pb (NO3)2 2PbO + 4NO2 + O2 PbO + 2[H] Pb + H2O 2) i) During lightning discharge the N2 present in the atmosphere reacts with the oxygen to form NO. N2 + O2 2NO ii) The NO is further oxidised to NO2. 2NO + O2 2NO2 iii) The nitrogen dioxide dissolves in the atmospheric moisture and in the presence of oxygen of the air forms HNO3 in the free state which is washed down by rain 4NO2+2H2O+O2 4HNO3 3) C + 4HNO3 CO2 + 2H2O + 4NO2 3Cu + 8HNO3 3Cu(NO3)2 + 4H2O + 2NO 200o c KHSO4 + HNO3 4) a) KNO3 + H2SO4 b) Conc. HCl is not used in place of conc. H2SO4 because HCl is volatile and hence nitric acid Vapours will carry HCl Vapours 34 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 10: Study of Compounds Nitric Acid 35 5) a) S + 6HNO3 H2SO4 + 2H2O + 6NO2 P + 5HNO3 H3PO4 + H2O + 5NO2 b) Acidic properties: Nitric acid in water solution is a very strong monobasic acid. HNO3 ionises almost completely in dilute aqueous solution to produce hydrogen ions and nitrate ions. HNO3(aq) H+ + NO3 i) It turns blue litmus red (ii) Reaction with alkalis:It neutralizes alkalies to form salt and water. c) 3SO2 + 2H2O + 2HNO3 3H2SO4 + 2NO 3H2S + 2HNO3 3S + 2NO + 4H2O d) Oxidising properties are due to nascent oxygen which it gives on decomposition. 2HNO3 (dil.) 2NO + H2O + 3[O] 2HNO3 (conc.) 2NO2 + H2O + [O] Nitric acid is a powerful oxidizing agent and the nascent oxygen formed on decomposition oxidizes hydrogen to water. 6) a) Cu + 4HNO3 Cu(NO3)2 + 2H2O + 2NO2 b) 2NaNO3 2NaNO2 + O2 (Slightly deliquescent) c) NH4NO3 Colourless Crystalline N2O(g) + 2H2O(vap) Nitrous oxide No residue left Laughing gas d) 2AgNO3 2Ag + 2NO2 + O2 7) a) NaOH + HNO3 NaNO3 + H2O b) CuO + 2HNO3 Cu(NO3)2 + H2O c) PbO + 2HNO3 Pb(NO3)2 + H2O d) Mg(OH)2 + 2HNO3 Mg(NO3)2 + 2H2O e) Fe(OH)3 + 3HNO3 Fe(NO3)3 + 3H2O f) HNO3 + 3HCl NOCl + 2H2O + 2[Cl] 8) Cu(NO3)2 2CuO + 4NO2 + O2 when Cu(NO3)2 is heated black CuO is obtained and brown fumes of NO2 escape. 9) a) 2KNO3 2KNO2 + O2 b) 2NaNO3 2NaNO2 + O2 b) NH4NO3 10) a) KNO3 11) Na2CO3 + 2HNO3 2NaNO3 + CO2 + H2O Volume 2 of 2 c) KNO3 Universal Tutorials X ICSE Chemistry 35 36 Chapter 11: Study of Compounds Sulphuric Acid Introduction Occurrence Sulphuric Acid Preparation Manufacture Properties Uses Tests for Sulphuric Acid and Sulphates Sulphuric acid: Molecular formula: H2SO4 Relative molecular mass: 98 O Structure: H O S O H O Introduction: Sulphuric acid is rightly called the King of Chemicals because there is no other manufactured compound which is used by such a large number of key industries. It was obtained as an oily viscous liquid by heating crystals of green vitriol, and was therefore known by the name of the oil of vitriol. 2FeSO4 . 7H2O Fe2O3 + SO2 + SO3 + 14H2O The sulphur trioxide evolved gets dissolved in water forming sulphuric acid. SO3 + H2O H2SO4 Occurrence: In Free State, it is found in certain mineral springs and is formed by the action of water on certain sulphides. In the combined state, as Barytes BaSO4, Gypsum CaSO4 . 2H2O and Kieserite MgSO4 . H2O etc. Preparation of Sulphuric Acid: By oxidation of an aqueous solution of sulphur dioxide with the following reagents: Atmospheric oxygen 2SO2 + 2H2O + O2 2H2SO4 Chlorine or bromine SO2 + 2H2O + Cl2 H2SO4 + 2HCl SO2 + 2H2O + Br2 H2SO4 + 2HBr Sulphur with conc. Nitric acid S + 6HNO3 H2SO4 + 6NO2 + 2H2O 36 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 11: 1 Study of Compounds C Sulphuric Acid A 37 Manu ufacture of Sulph huric Aci id (Conta act Proce ess): The e various step ps in the Con ntact process s are as follo ows: Prod duction of su ulphur dioxide e: Sulphur S dioxi ide is produc ced by roasting iron pyrite es (FeS2) 4FeS2 + 11O2 2Fe2O3 + 8SO2 or by burnin ng Louisiana a sulphur (99.5% pure) in purified air. S + O2 SO S 2 Pa arts of the plant p Blo ower Su ulphur or iron pyr rite burners Du usting chamb ber Co ooling pipes Sc crubbing towe er Dry ying tower Ars senic purifier r Testing box Co ontact tower Ab bsorption tow wer Dilution tank n Function For passage p of purified p air or r oxygen. For production p of f sulphur dioxide by burn ning sulphur o or iron pyrite es. For removal r of dust particles by downwar rd blow off st team. For cooling c the gases g by pas ssage through isolated pipes. f remo oval of impur rities and dust particles b by downwar rd spray For further of wa ater. For drying d moist gases by do ownward spra ay of conc. H2SO4 For removing r ars senic oxide by b passage over o ferric hy ydroxide. For testing the purity of th he gases by b passage of light through a darkened box. For catalytic c oxid dation of SO2 to SO3 by passage of s sulphur diox xide and oxyg gen through iron tower packed with h vanadium pentoxide catalyst initia ally heated to o 450 C t vapo ours by des scending str ream of For absorption of sulphur trioxide c. H2SO4 [98% %] conc For dilution d of ole eum by flow of required amount a of wa ater. Puri ification of ga ases: T The mixture of sulphur dioxide d and air contains s various impurities whic ch must be removed, o otherwise the e catalyst los ses its efficiency. The T mixture is passed thr rough a purif fier called ele ectric precipitator consist ting of a cham mber with w wires at high h electric pot tential. The electric e charg ge attracts solid s particles s which are removed. T mixture is then led to The o a water scr rubber where e it is comple etely freed fro om dust part ticles. It is t then dried by y a spray of concentrated d sulphuric acid a in anoth her chamber. It then goes into the a arsenic purifier where eve ery trace of arsenic a oxide e is removed d. Oxid dation of sulp phuric dioxid de to sulphur trioxide: T The clean dr ried gaseous s mixture of sulphur s diox xide and air is passed thr rough a towe er loosely p packed with vanadium pentoxide or platinum on perforated shelves. s The e catalyst is placed in Volume 2 of 2 U Universal Tuto orials X ICS SE Chemistr ry 37 38 vertical iron pipes inside a cylindrical iron tower called the converter. Here the preheated mixture of sulphur dioxide and air (oxygen) on passing through catalyst pipes forms sulphur trioxide. 2SO2 + O2 V2O5 450 C 2SO3 Since the reaction is highly exothermic, the catalyst is heated only in the beginning to about 450 C. This temperature is maintained by the heat evolved during the reaction. Absorption of sulphur trioxide in sulphuric acid: The gas is cooled in a heat exchanger and is then absorbed in another tower in concentrated sulphuric acid. Sulphur trioxide forms fuming sulphuric acid also called oleum or pyrosulphuric acid. SO3 + H2SO4 H2SO4 (oleum) Dilution of oleum: It is diluted by adding calculated amount of water to obtain concentrated sulphuric acid of the desired strength (98%). H2S2O7 + H2O 2H2SO4 Favourable conditions for the conversion of SO2 to SO3 (contact process): z z z z Exothermic reactions are favoured by low temperature: The temperature should be as low as possible. The yield has been found to be maximum at about 410 450 C. High pressure: High pressure favours the reaction because product formed has less volume than reactant. But the acid resistant towers which are able to withstand high pressure are difficult to build. Hence the pressure of 1 2 atmospheres is used. Excess of oxygen: This increases the production of sulphur trioxide. A suitable catalyst: Platinum is more efficient as a catalyst than vanadium pentoxide (V2O5) but it is more expensive. Also it gets easily poisoned by impurities like arsenic (III) oxide. Vanadium pentoxide, though less efficient is cheaper and not affected by impurities. Therefore, it is used as a catalyst. Note: 1) Dilution of concentrated sulphuric acid is done only by addition of acid to water. i) When the acid is added to water in a controlled manner, acid being heavier settles down and the evolved heat is dissipated in the water itself and hence the spurting of the acid is minimized. ii) If water is added to the acid, there is a sudden increase in temperature and the acid being in bulk tends to spurt out with serious consequences. 2) Sulphuric acid cannot be concentrated by boiling or distillation after certain concentration. On boiling, the pure acid decomposes giving off water vapour and dense white fumes of sulphur trioxide. More sulphur trioxide is lost than water until the concentration of the acid is reduced to 98.33%. The acid of this concentration boils at 338 C as a constant boiling mixture. Thus, dilute acid cannot be concentrated beyond 98.33%. Hundred per cent acid is prepared by dissolving sulphur trioxide in the concentrated acid. 38 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 11: Study of Compounds Sulphuric Acid 39 Properties of Sulphuric Acid: Physical Properties: Colour Odour Taste Nature Density Boiling point Colorless Odourless. Slightly sour in taste. Dense, oily, hygroscopic liquid. It absorbs moisture, so H2SO4 should always be kept in stoppered. Pure acid : 1.85 g/cc. 338 C. Melting point Pure sulphuric acid freezes to colourless crystals at 10.4 C. Solubility Conductivity Constant boiling mixture Physiological nature Soluble in water in all proportions. Pure acid : Almost a non conductor of electricity. Forms a constant boiling mixture at 338 C containing 98.5% of the acid. Concentrated acid is highly corrosive in nature and chars the skin black. Chemical Properties: z The chemical properties of sulphuric acid depend very much on whether the acid is dilute or concentrated. Properties of dilute sulphuric acid z Acidic property: Pure sulphuric acid is not an acid as it does not ionise. It is acidic only in water solution when hydronium and sulphate ions are formed. Hydronium ion results in the acidic properties. It ionises in two stages, so it is a dibasic acid. H2SO4 + H2O H3O+ + HSO 4 z It reacts with metals, which are above hydrogen in the activity series to form metallic sulphate and hydrogen at ordinary temperature. Mg + H2SO4 MgSO4 + H2 z Zn + H2SO4 ZnSO4 + H2 Fe + H2SO4 FeSO4 + H2 It neutralizes bases (oxides and hydroxides) to form salts and water. CuO + H2SO4 CuSO4 + H2O z + 2 HSO 4 + H2O H3O + SO 4 NaOH + H2SO4 NaHSO4 + H2O FeO + H2SO4 FeSO4 + H2O 2NaOH + H2SO4 Na2SO4 + 2H2O It liberates carbon dioxide from metallic carbonates and bicarbonates. ZnCO3 + H2SO4 ZnSO4 + H2O + CO2 2NaHCO3 + H2SO4 Na2SO4 + 2H2O + 2CO2 z 2KHCO3 + H2SO4 K2SO4 + 2H2O + 2CO2 It evolves hydrogen sulphide from metal sulphides. Na2S + H2SO4 Na2SO4 + H2S z FeS + H2SO4 FeSO4 + H2S ZnS + H2SO4 ZnSO4 + H2S It evolves sulphur dioxide from sulphites and hydrogen sulphites. Na2SO3 + H2SO4 Na2SO4 + H2O + SO2 2Na2HSO3 + H2SO4 Na2SO4 + 2H2O + 2SO2 Volume 2 of 2 Universal Tutorials X ICSE Chemistry 39 40 Properties of concentrated sulphuric acid: z Non volatile nature: Concentrated sulphuric acid has a high boiling point (356 C) and so, it is considered to be a non volatile acid. Therefore, it is used for preparing volatile acids like hydrochloric acid, nitric acid and acetic acid from their salts by double decomposition. Salt of volatile acid + Acid (conc.) Acid salt + Volatile acid z NaCl + H2SO4 NaHSO4 + HCl As a dehydrating agent: H2SO4 has a great affinity for water. It removes readily, elements of water from other compounds i.e., it acts as a dehydrating agent. Organic acids and organic compounds are dehydrated by conc. H2SO4 as follows: Conc .H2SO4 HCOOH CO + H2O All carbohydrates such as glucose, sugar, and cellulose react immediately to give a black spongy mass of carbon which rises up. Steam is given off and the whole mass gets heated due to an exothermic reaction. They are said to be charred. Conc .H2SO4 C6H12O6 6C + 6H2O Glucose Conc. sulphuric acid removes water of crystallisation from salts. For example, blue copper (II) sulphate CuSO4.5H2O taken in a test tube becomes white anhydrous copper sulphate, when a few drops of conc. sulphuric acid are added. H2SO4 CuSO4.5H2O CuSO4(s) Blue Dirty white + 5H2O (Removed by acid) Conc. H2SO4 reacts with skin to give blisters because of removal of water. z As an oxidising agent: The oxidising property of concentrated sulphuric acid is due to the fact that on thermal decomposition, it yields nascent oxygen [O]. H2SO4 H2O + SO2 + [O] Nascent oxygen oxidizes non metals, metals and inorganic compounds. Non metals: Carbon: C + 2 H2SO4 CO2 + 2H2O + 2SO2 Sulphur: S + 2H2SO4 3SO2 + 2H2O Phosphorus: 2P + 5H2SO4 2H3PO4 + 2H2O + 5SO2 Metals Copper: Cu + 2H2SO4 CuSO4 + 2H2O + SO2 Zinc: Zn + 2H2SO4 ZnSO4 + 2H2O + SO2 Inorganic compounds Hydrogen bromide: 2HBr + H2SO4 Br2 + 2H2O + SO2 Hydrogen sulphide: H2S + H2SO4 S + 2H2O + SO2 Uses of Sulphuric Acid: It is used in the preparation of (a) Iodine (b) Carbon monoxide (c) carbon dioxide (d) hydrogen Metallurgy: (a) Extraction (b) Pickling metals In lead accumulators: It undergoes electrolysis in the aqueous state. 40 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 11: Study of Compounds Sulphuric Acid 41 Oil refining: Sulphuric acid is used to remove harmful impurities in purification of oil products eg. petrol, kerosene and lubricants. Industrial uses: in the manufacture of: Fertilizers: (a) Ammonium sulphate [(NH4)2SO4] (b) Superphosphate of lime [Ca(H2PO4)2 + CaSO4] Dyes, drugs: Artificial fibres (I) Rayon (II) Nylon (b) Dyes, drugs [from coal tar derivatives] Explosives: (a) Tri nitro toluene [T.N.T.] (b) Picric acid (c) Tri nitro glycerine [C3H5O3(NO2)3] Acids: (a) Nitric acid [HNO3] (b) Hydrochloric acid [HCl] (c) Phosphoric acid [H3PO4] (d) Acetic acid [CH3COOH] Compounds: (a) Sodium sulphate [glass industry] (b) Ferrous sulphate [ink industry] PREVIOUS YEARS BOARD QUESTIONS: Year 2013: 1) From the list given below, select the word (s) required to correctly complete blanks (i) to (v) in the following passage. The words from the list are to be used only once. Write the answers as (a) (i), (ii), (iii) and so on. Do not copy the passage. [ammonia, ammonium, carbonate, carbon dioxide, hydrogen, hydronium, hydroxide, precipitate, salt, water] i) A solution M turns blue litmus red, so it must contain (i) _________ ions; another solution O turn red litmus blue and hence, must contain (ii) _________. ii) When solutions M and O are mixed together, the products will be (iii) _________ and (iv) _________. iii) If a piece of magnesium was put into a solution M, (v) _________ gas would be evolved. [5] Year 2012: 1) Name the gas in each of the following: i) The gas evolved on reaction of Aluminium with boiling concentrated caustic alkali solution. ii) The gas produced when excess ammonia reacts with chlorine. iii) A gas which turns acidified potassium dichromate clear green. iv) The gas produced when copper reacts with concentrated nitric acid. v) The gas produced on reaction of dilute sulphuric acid with a metallic sulphide. 2) Identify the anion present in the following compounds: i) Compound X on heating with copper turnings and concentrate sulphuric acid liberate a reddish brown gas. ii) Compound Z which on reacting with dilute sulphur acid liberates a gas which turns lime water milky, but the gas has no effect on acidified potassium dichromate solution. iii) Compound L on reacting with Barium chloride solution gives a white precipitate insoluble in dilute hydrochloric acid or dilute nitric acid. Year 2008: 1) Select the correct answer from the choices A, B, C, D which are given. Which of the following reactions is used to prepare sulphuryl chloride? A) Adding concentrated sulphuric acid to a chloride B) Passing sulphur dioxide through a solution of chlorine C) Reacting dry sulphur dioxide and dry chlorine. D) Reacting dilute sulphuric acid with a solution of chlorine. [1] 2) Identify the following substances: i) Gas (C) has an offensive smell like rotten eggs. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 41 42 ii) Gas (D) is a colourless gas which can be used as a bleaching agent. [2] 3) Write the equation for the following reactions: i) Sulphur dioxide and water ii) Dilute sulphuric acid and barium chloride iii) Dilute sulphuric acid and sodium sulphide 4) i) What is the property of concentrated sulphuric acid which allows it to be used in the preparation of hydrogen chloride and nitric acid? ii) What property of concentrated sulphuric acid is in action when sugar turns black in its presence? 5) Copy and complete the following table relating to important industrial process. Output refers to the product of the process not the intermediate steps. [3] Name of Process Inputs Catalyst Equation for catalysed reaction Output Contact process Sulphur dioxide + Oxygen Year 2007: 1) Some properties of sulphuric acid are listed below. Choose the property A, B, C, or D which is responsible for the reactions (i) to (v). Some properties may be repeated: A) Acid B) Dehydrating agent C) Non-volatile acid D) Oxidizing agent i) C2H22O11 + nH2SO4 12C + 11H2O + nH2SO4 ii) S + 2H2SO4 3SO2 + 2H2O iii) NaCl + H2SO4 NaHSO4 + HCl iv) CuO + H2SO4 + CuSO4 + H2O v) Na2CO3 + H2SO4 Na2SO4 + H2O + CO2 [5] 2) i) Name the acid formed when sulphur dioxide dissolves in water. ii) Name the gas released when sodium carbonate is added to a solution of sulphur dioxide. iii) What are the two necessary conditions for the direct combination of sulphur dioxide and chlorine forming sulphuryl chloride? iv) State the property of sulphur dioxide which causes potassium permanganate to change its colour from purple to colourless. [5] 3) i) HCl, HNO3 and H2SO4 are the formulae of three compounds. Which of these compounds has the highest boiling point and which has the lowest? ii) Dilute hydrochloric acid and dilute sulphuric acid are both colourless solutions. How will the addition of barium chloride solution to each help to distinguish between the two? [3] Year 2006: 1) What do you observe when sulphur dioxide is passed through a jar containing bromine water? [1] 2) i) Name the process used for the large scale manufacture of sulphuric acid. ii) Which property of sulphuric acid accounts for its use as a dehydrating agent? iii) Concentrated sulphuric acid is both an oxidizing agent and a non-volatile acid. Write one equation each to illustrate the above mentioned properties of sulphuric acid. [4] 3) Give reasons for the following: i) Carbon dioxide and sulphur dioxide cannot be distinguished by using lime water. ii) Sulphur dioxide is used as an antichlor. [2] Year 2005: 1) Write balanced chemical equation for the reaction of potassium hydrogen carbonate with dilute sulphuric acid. [1] 2) The bleaching action of chlorine is permanent whereas the bleaching action of sulphur dioxide is temporary. In this context, 42 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 11: Study of Compounds Sulphuric Acid 43 i) Give a reason why chlorine is not used to bleach silk. ii) State the similarity in the use of sulphur dioxide and chlorine as bleaching agents. iii) Explain the bleaching action of sulphur dioxide with the help of chemical equations. iv) Why is bleaching by sulphur dioxide only temporary? [5] 3) A, B, C and D summarize the properties of sulphuric acid depending on whether it is dilute or concentrated. Choose the property (A, B, C or D) depending on which is relevant to each of the preparations (i) to (iii). A) Dilute acid (typical acid property) B) Non-volatile acid C) Oxidizing agent D) Dehydrating agent. i) Preparation of hydrogen chloride ii) Preparation of ethene from ethanol iii) Preparation of copper sulphate from copper oxide. [3] CLASS WORK EXERCISE: 1) Why water is not added to concentrated H2SO4 in order to dilute it? 2) Why the impurity of arsenic oxide must be removed before passing the mixture of SO2 and air through the catalytic chamber? 3) Give a test of sulphuric acid where an insoluble white precipitate is formed. 4) Write a reaction when copper is heated with concentrated sulphuric acid 5) Give a chemical test to distinguish between Dilute sulphuric acid and conc. Sulphuric acid. 6) Give reasons for the following. a) Sulphuric acid forms two types of salts with NaOH. b) Red brown vapours are produced when concentrated sulphuric acid is added to potassium bromide. c) A piece of wood becomes black when concentrated sulphuric acid is poured on it. d) Brisk effervescence is seen when oil of vitriol is added to sodium carbonate. 7) Why is: a) Concentrated sulphuric acid kept in air tight bottles? b) H2SO4 is not a drying agent for H2S? c) Sulphuric acid is used in the preparation of HCl and HNO3? Give equations in both cases. 8) What property of conc. H2SO4 is made use of in each of the following cases? Give an equation for the reaction in each case, a) In the production of HCl gas when it reacts with a chloride. b) In the preparation of CO from HCOOH. c) As a source of hydrogen by diluting it and adding a strip of magnesium. d) In the preparation of sulphur dioxide by warming a mixture of conc. Sulphuric acid and copper-turnings. e) Hydrogen sulphide gas is passed through concentrated sulphuric acid 9) What is the name given to the salts of sulphurous acid? 10) Why is sulphuric acid considered to be dibasic acid? 11) What do you observe, when sulphuric acid is added to blue copper sulphate crystals? 12) Name all the products formed: when Copper is heated with concentrated sulphuric acid. 13) What is the function of conc. Sulphuric acid in the preparation of CO from oxalic acid? 14) Explain the following: a) In the manufacture of sulphuric acid by the contact Process, great care is taken to purify the mixture of air and sulphur dioxide, especially to free it from arsenic impurities. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 43 44 15) 16) 17) 18) 19) 20) 21) 22) 23) 24) 25) 26) 27) 28) 29) 44 b) Whenever water is added to concentrated sulphuric acid or concentrated sulphuric acid is added to water, a large amount of heat is liberated. But the acid dangerously spurts out only when water is added to the concentrated acid. Name the anion [negative ion] present in the following compound: Compound D when warmed with dil. H2SO4 gives a gas which turns acidified potassium dichromate solution green. Name two other acids other than sulphuric acid which can be prepared by using sulphuric acid. In using sulphuric acid to prepare the acids as mentioned in (16) above, which property of sulphuric acid is used? Write balanced equations for the three chemical reactions that take place during the conversion of sulphur dioxide to sulphuric acid in the contact process. a) Name the oxide of sulphur which reacts with water to give sulphuric acid. b) In the Contact Process, the direct reaction between the oxide of sulphur and water is avoided. In this process, with what does the oxide of sulphur react instead of water and what is the name of the product? c) Give the name and formula of the acid salt which can give sodium ions and sulphate ions in solutions. a) Name one catalyst used industrially which speeds up the conversion of sulphur dioxide to sulphur trioxide in the production of sulphuric acid in the laboratory or industrially. b) Write the equation for the conversion of sulphur dioxide to sulphur trioxide. Why does this reaction supply energy? What is the name of the compound formed between sulphur trioxide and sulphuric acid? Explain how a reagent chosen from : Ammonium hydroxide, Barium chloride, Sodium chloride, Sodium hydroxide, Sulphuric acid and Nitric acid enables to distinguish between the two acids mentioned therein. From the following gases ammonia, chlorine, hydrogen chloride, sulphur dioxide, select the gas that matches the description given below and answer the questions that follow: Gas A is a reducing agent which contains oxygen. i) What is the name of gas? ii) What would you observe if gas A is bubbled through acidified potassium dichromate solution? Gases can be prepared using the substance along with dilute or concentrated sulphuric acid. State the substance/s reacted with dilute or concentrated sulphuric acid to form the following gases: i) Hydrogen ii) Carbon dioxide Name a gas which smells of rotten eggs. Write observations and balanced equations for the reaction: A paper dipped in potassium permanganate solution is put on the mouth of a test tube containing sulphur dioxide gas. What is the name of the process by which sulphuric acid is manufactured? Name the catalyst used in the process Complete the following sentence choosing the correct word from the brackets concentrated sulphuric acid is used in the laboratory preparation of nitric acid and hydrochloric acid because it is ______ [less volatile/stronger] in comparison to these two acids . From the gases ammonia, hydrogen chloride, hydrogen sulphide, sulphur dioxide select the following i) This gas can be oxidized to sulphur ii) This gas decolourises potassium permanganate solution. iii) This gas can be obtained by the reaction between copper and concentrated sulphuric acid. Write the equation for the reaction by which sulphur dioxide is converted to sodium sulphite. Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 11: Study of Compounds Sulphuric Acid 45 HOME WORK EXERCISE: 1) Give two balanced reactions of each type to show the following properties of sulphuric acid. a) Acidic Nature. b) Oxidising agent c) Hygroscopic nature d) Non-volatile nature 2) Name the products formed when hot and concentrated sulphuric acid reacts with the following: a) CuSO4. 5H2O b) NaOH c) Sugar d) Carbon e) Sulphur 3) Write balanced equations for the reactions in the preparation of the following: Sulphuric dioxide by the action of hot concentrated sulphuric acid on sulphur. 4) Write balanced equations for the reaction of dilute sulhuric acid with each of the following: a) Copper carbonate b) Lead nitrate solution c) Zinc hydroxide 5) Write the equation for the following reactions: a) Dilute sulphuric acid producing hydrogen. b) Between lead nitrate solution and dilute sulphuric acid. 6) Write the balanced equation for the reaction of dilute hydrochloric acid and sodium sulphite. 7) Write the equations for the laboratory preparation of: i) Sodium sulphate using dilute sulphuric acid ii) Lead sulphate using dilute sulphuric acid. iii) Copper sulphate from copper ANSWERS Home Work answers: 1) a) H2SO4 + H2O H3O+ + HSO 4 + 2 HSO 4 + H2O H3O + SO4 i) It reacts with metals above hydrogen in the activity series to form hydrogen at ordinary temperature. Mg + H2SO4 MgSO4 + H2 ii) It neutralizes bases (oxides and hydroxides) to form salts and water. CuO + H2SO4 CuSO4 + H2O b) Oxidising agent: The oxidizing property of conc. H2SO4 is due to the fact that on thermal decomposition it yields nascent oxygen (O). H2SO4 H2O + SO2 + [O] Nascent oxygen oxidizes non metals, metals and inorganic compounds. Non metals, C + H2SO4 CO2 + 2H2O + 2SO2 ; S + 2H2SO4 3SO2 + 2H2O conc. H SO 2 4 c) Hygroscopic nature: HCOOH CO + H2O conc. H SO 2 4 6C + 6H2O C6H12O6 d) Non volatile nature, NaCl + H2SO4 NaHSO4 + HCl; NaNO3 + H2SO4 NaHSO3 + HNO3 conc. H SO 2 4 2) a) CuSO4 5H2O CuSO4(s) (dirty white) + 5H2O b) 2NaOH + H2SO4 Na2SO4 + 2H2O conc. H SO 2 4 c) Sugar C6H12O6 6C + 6H2O d) C + H2SO4 CO2 + 2H2O + SO2 e) S + 2H2SO4 3SO2 + 2H2O 3) S + 2H2SO4 3SO2 + 2H2O 4) CuCO3 + dil. H2SO4 CuSO4 + H2O + CO2 Volume 2 of 2 Universal Tutorials X ICSE Chemistry 45 46 Pb(NO3)2 + dil. H2SO4 PbSO4 + 2HNO3 Zn(OH)2 + dil. H2SO4 ZnSO4 + 2H2O 5) a) Zn + H2SO4 ZnSO4 + H2 b) Pb(NO3)2 + H2SO4 PbSO4 + HNO3 6) Na2SO3 + 2HCl 2NaCl + H2O + SO2 7) i) Na2SO3 + H2SO4 Na2SO4 + H2O + SO2 ii) Pb(NO3)2 + H2SO4 (dil.) 2HNO3 + PbSO4 iii) Cu + 2H2SO4 CuSO4 + 2H2O + SO2 46 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry 47 Chapter 12: Organic Chemistry 12A Organic Compounds 12D Hydrocarbons: Alkynes Introduction Introduction Unique Homologous Series Functional Group Isomerism Hydrocarbons Structure of ethyne Alkyl Group Preparation of ethyne Homologous Series Physical and Chemical Properties Nomenclature Uses 12B Hydrocarbons: Alkanes 12E Alcohols Introduction Introduction Homologous Series Homologous Series Isomerism Preparation of Ethanol Structure of Methane Physical and Chemical Properties Preparation of Methane & Ethane Uses Physical and Chemical Properties Commercial Forms of ethanol Uses 12F Carboxylic Acids Introduction 12C Hydrocarbons: Alkenes Introduction Homologous Series of Monocarboxylic acids Homologous Series Preparation of acetic acid Isomers Physical and Chemical Properties Structure of Ethene Test Preparation of Ethene Uses Physical and Chemical Properties Uses 12A: Organic Compounds: Introduction: The word organic means pertaining to life. People thought that substances like sugar, starch, protein and acetic acid could be obtained only from living sources like plants and animals. So they called such substances organic compounds and the chemistry dealing with them organic chemistry. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 47 48 Since these organic compounds were obtained straight from nature and there was no known method of preparing them in the laboratory, it was believed that they were the products of some vital force of nature. The vital force theory of organic compounds was soon discarded when, in 1828, a German chemist named Friedrich Wohler showed that it was possible to obtain urea etc. the organic compounds from laboratory processes. NH4CNO heat CO(NH2)2 (Ammonium cyanate) (Urea) In 1845, Kolbe prepared acetic acid (CH3COOH) from its constituent elements, carbon, hydrogen and oxygen. Berthelot, in 1856, synthesized methane gas (CH4). In this manner the old concept of organic chemistry was given up and it was accepted that organic chemistry is essentially the chemistry of carbon compounds. Organic Compounds: Sources of organic compounds: Plants, Animals, Coal, Petroleum, Fermentation, Wood, Synthetic Methods. Comparison between organic and inorganic compound. Organic compound Presence of carbon: Carbon is a necessary element in every organic compound. 2) Solubility in water: They generally do not dissolve in water. 3) Solubility in the organic solvents: They dissolve in organic solvents like alcohol, benzene and chloroform. 4) Melting and boiling point: They have low m.p. and b.p. and easily decompose on heating. 5) Combustibility: They are inflammable, i.e. they catch fire easily. 6) Bonding: They form covalent bonds. 7) Conductivity: They are non electrolytes. 8) Isomerism: They show the phenomenon of isomerism 9) Colour and smell: Organic compounds have characteristic colour and odour. 10) Reactions: Molecular reactions are slow, due to the presence of covalent linkages. These reactions never proceed to completion. 1) Inorganic compound Carbon is not an essential element in inorganic compounds. They generally dissolve in water. All inorganic compounds do not dissolve in organic solvents. They have high m.p. and b.p. and usually do not decompose on heating. They do not burn easily. Most of them form ionic bonds. Only those that form ionic bonds are good electrolytes. No such phenomenon is shown by inorganic compounds. Most of them are colourless and odourless. They give reactions which are fast, ionic and take place to completion. Unique Nature of Carbon Atoms: Carbon shows, tetravalency and catenation and most of its compounds form isomers. Tetravalency of the carbon atom: This characteristic of the carbon atom, by virtue of which it forms four covalent bonds, is called the tetravalency of carbon. X XCX X 48 | C | Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry 49 Catenation: Carbon can combine with other carbon atoms (self linking) due to great strength of carbon carbon bonds to form chains. This property of self linking of carbon atoms through covalent bonds to form long straight or branched chains and rings of different sizes is known as catenation. Formation of straight, branched and cyclic chains of carbon atoms: The combination of carbon atoms with one another gives rise to straight or branched or cyclic chains. | | | | C C C C | | | | (Straight chain) | | | C C C | | | - C | (Branched chain) C C | C C | C C (Cyclic or closed chain) Formation of single, double and triple covalent bonds: The valency of carbon is four, i.e. it is tetravalent. In order to satisfy its valency, it forms single, double and triple covalent bonds by sharing one, two or three pairs of electrons respectively between two carbon atoms. | | C C | | (single bond) | | C=C | | (double bond) C C (triple bond) Isomerism: Compounds that are represented by the same molecular formulae but by different structural formulae are called isomers, while the phenomenon is known as isomerism. In the case of the organic compounds, a given molecular formula may represent more than one compound. For eg. Molecular formula C2H6O stands for alcohol as well as ether CH3CH2OH Ethyl alcohol; CH3OCH3 Dimethyl ether Functional Group: A functional group is an atom or a group of atoms that defines the structure (or the properties of a particular family) of organic compounds, for eg. Halides: F, Cl, Br; Aldeyhydes: CHO; Hydroxyl: OH; Carboxylic acids: COOH Alkanes do not contain any functional group. The functional group of alkenes is > C = C < while in alkynes it is C C . Characteristics of functional groups: z The chemical properties of the compounds containing the same functional group are similar. Therefore, the compounds of the same functional groups are identified using the same type of tests. z The physical and chemical properties of the compounds of different functional groups are different. z There exists a homologous series of compounds containing a particular type of functional group. For example, the homologous series of alcohols is CH3OH, C2H5OH and C3H7OH. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 49 50 Hydrocarbons: Hydrocarbons are compounds which are made up only of carbon and hydrogen. Hydrocarbons have molecular formula CxHy, where x and y are whole numbers. They are regarded as parent organic compounds since other organic compounds may be derived from them by replacement of one or more hydrogen atoms. Example: Carbon tetrachloride CCl4 is formed by replacing 4 hydrogen atoms by chlorine. CH4 + 4Cl2 CCl4 + 4HCl Classification of Hydrocarbons: Hydrocarbons are sub divided into two main groups, the aliphatic (open) and cyclic (closed) chain compounds. The open chain compounds are further sub divided into saturated compounds and unsaturated compounds. Hydrocarbons Aliphatic or open chain compounds Saturated alkanes (paraffins) CnH2n+2 Cyclic or closed chain compounds Unsaturated Alkenes (Olefins) CnH2n Alkynes CnH2n 2 | | | - C - C - C | | | The simplest hydrocarbon is alkane. It is represented by the formula CnH2n+2, where n represents natural number. It is a saturated hydrocarbon as all the four valencies of carbon are satisfied by single covalent bonds. Alkanes: z \ / \ | | C=C C=C C / \ / | Compounds where all the four valencies are not satisfied by single covalent bonds, double or triple bonds are required to satisfy the valencies. Alkenes: z z They are known as unsaturated compounds like Alkenes (CnH2n) are the hydrocarbons with double bond and Alkynes (CnH2n 2) are the hydrocarbons with triple bond between two carbon atoms. Alkynes: C C | C C C | Comparison of Saturated and Unsaturated Hydrocarbons: Saturated organic compounds All the four valencies of each carbon atom are satisfied by forming single covalent bonds with carbon and with hydrogen atoms. 50 Unsaturated organic compounds The valencies of at least two carbon atoms are not fully satisfied by the hydrogen atoms. Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry 51 Saturated organic compounds Unsaturated organic compounds Carbon atoms are joined only by a single covalent bond. | | C C | | Carbon atoms are joined by double covalent bonds >C=C< or by triple covalent bonds. - C C They are less reactive due to the non availability of electrons in the single covalent bond and therefore they undergo substitution reaction. They are more reactive due to the presence of electrons in the double or the triple bond, and therefore undergo addition reaction. Cycle or Closed Chain Hydrocarbons: z These compounds contain three or more carbon atoms in their molecules. They are also called carbocylic compounds. These cyclic compounds are further divided into alicyclic hydrocarbons and aromatic hydrocarbons. Alkyl Group: An alkyl group is obtained by removing one atom of hydrogen from an alkane molecule. H CnH2n+1 CnH2n+2 Alkane Alkyl Thus general formula of alkyl is CnH2n+1 H C2H5 CnH6 ethane ethyl Structure and Isomers: Structure: Hydrocarbons are usually represented by their structural formulae. The formula that shows how atoms of different elements are linked together in a molecule is known as structural formula. For eg. Butane (C4H10) can be represented in the following way. H H H H | | | | Structural formula H C C C C H | | | | H H H H A molecule having the bigger structural formula is often cumbersome. We represent it by abbreviated formula or sometimes even by carbon skeleton. Abbreviated or condensed formula: CH3 CH2 CH2 CH3 Carbon skeleton: C C C C A structure that shows only the linking of carbon atoms in a molecule is called the carbon skeleton. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 51 52 Isomers: Compounds which have the same molecular formula but have different arrangements of atoms (structural formula) with respect to one another and thus form different compounds having different physical and chemical properties are known as ISOMERS and the phenomenon as ISOMERISM ISOMERISM Stereoisomerism or space isomerism Structural Isomerism Chain Position Functional There are two main causes of isomerism Metamerism Difference in the mode of linking of atoms: For example: C4H10O shows different types of linkages and thus it stands for three different types of ether. C2H5 O C2H5 CH3 O C3H7 CH3 O CH(CH3)2 Diethyl ether Methyl propyl ether Methyl iso propyl ether This type of isomerism is structural isomerism. Difference in the geometrical arrangement of atoms or groups in space For example: 1, 2 dichloro ethene H H H Cl C=C C=C Cl Cl Cl H This type of isomerism is stereo isomerism. Different types of structural isomerism are: Chain Isomerism: When two or more compounds have a similar molecular formula but are different in the arrangement of carbon atoms in straight or branched chains. These compounds are referred to as chain isomers and the phenomenon is termed as chain isomerism. For example: Pentane C5H12 CH3 | CH3 CH3 C CH3 | | CH3CH2CH2CH3 CH3CHCH2CH3 CH3 Pentane iso-pentane (2-methyl butane) neo-pentane (2, 2-dimethyl propane) Position isomerism: When two or more compounds with the same molecular formula differ in the position of substituent atom or functional group on the carbon atom, they are called position isomers and this phenomenon is termed position isomerism. For example: and CH3 C C CH3 i) CH3 CH2C C H but-1-yne ii) but- 2-yne CH3CH = CH CH3 but-2-ene and CH2 = CH CH2 CH3 but 1 ene Homologous series: A homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by a CH2 group. 52 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry 53 Examples of Homologous Series: Alkane Methane Ethane Propane Butane Alkene Ethene Propene Butene Alkyne Ethyne Propyne Butyne Alcohols Methanol Ethanol Propanol Butanol Gen. Formula CnH2n+2 CH4 C2H6 C3H8 C5H10 Gen. formula CnH2n C2H4 C3H6 C4H8 Gen. formula CnH2n 2 C2H2 C3H4 C4H6 Gen. formula CnH2n+1OH CH3OH C2H5OH C3H7OH C4H9OH Characteristics of a homologous series: Each member of the series differs from the preceding one by the addition of CH2 group and by 14 amu molecular mass. All members of a homologous series share a general formula. For example, the general formula for alkane is CnH2n+2, alkene is CnH2n. The physical properties of the members change gradually as the number of carbon atoms per molecule increases, i.e. as molecular mass increases. For eg. melting point, boiling point and the density of the successive members of the homologous series increase with the increase in molecular mass. The chemical properties show gradient similarity. For example: Methane reacts with chlorine to form methyl chloride. CH4 + Cl2 CH3Cl + HCl Similarly ethane reacts to form ethyl chloride. All the members of a homologous series can be prepared by using the same general method of preparation. For example: Alcohols are prepared by alkyl halides. z boil CH3Br + KOH CH3OH + KBr, z boil C2H5Br + KOH C2H5OH + KBr (aqueous) Nomenclature: Nomenclature was systematized by the chemists of IUPAC (International Union of Pure and Applied Chemistry) in 1957. According to this system, the name of an organic compound consists of three parts: (i) word root (ii) suffix (iii) prefix. Word root: It depends upon the number of carbon atoms in the longest carbon chain selected. Number of carbon atoms One carbon atom C1 Two carbon atoms C2 Three carbon atoms C3 Volume 2 of 2 Word root (Greek name) Meth Eth Prop Universal Tutorials X ICSE Chemistry 53 54 Number of carbon atoms Word root (Greek name) Four carbon atoms C4 But Five carbon atoms C5 Pent Six carbon atoms C6 Hex Seven carbon atoms C7 Hept Eight carbon atoms C8 Oct Nine carbon atoms C9 Non Ten carbon atoms C10 Dec Suffix: The word root is followed by an appropriate suffix, which represents the nature of the bond in a carbon carbon atom Nature of Bond Single bond (C C) Double bond (C = C) Triple bond (C C) Group (R ) Suffix ane ene yne yl General name Alkane Alkane Alkyne Alkyl General formula CnH2n+2 CnH2n CnH2n 2 CnH2n+1 Prefix: It denotes the substituent, alkyl or functional group and its position in the carbon chain. 1 2 3 4 5 C C C C C | CH3 2 Methyl (because methyl is attached to second C) In naming an organic compound, the simple rules are followed: z Selection of carbon chains: Choose the longest carbon chain. The compound is then named as the derivative of the alkane which corresponds to the longest chain. 1 2 3 1 2 3 4 5 C C C C C C C C C C | | C C C C C C C C 4 5 6 7 Right Wrong z The branch chains are considered to be substituent and their positions are indicated by the number of carbon atoms to which they are attached. 1 2 3 4 5 C C C C C | CH3 2 Methyl (because methyl is attached to second C) z 54 The carbon atoms of the longest chain alkyl groups (substituent) get the smallest possible number. 1 2 3 4 5 1 2 3 4 5 C C C C C C C C C C | | CH3 CH3 2 Methyl 4 Methyl Right Wrong Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry z 55 In case, any functional group is present in the chain, the carbon atoms are numbered in such a way that the functional group gets the smallest possible number. 5 4 3 2 1 CH3 CH CH2 CH CH3 | | CH3 OH 4 methyl pentan 2 ol Right z 1 2 3 4 5 CH3 CH CH2 CH CH3 | | CH3 OH 2 methyl pentan 4 ol Wrong In case different types of substituent are attached to the chain, they are arranged and named alphabetically. 1 2 3 4 5 6 CH3 CH CH2 CH CH2 CH3 | | Br Cl 2 Bromo 4 chloro hexane z The position(s) of alkyl group(s) are indicated by writing the position and name of the alkyl group just before the name of parent hydrocarbon. CH3 CH CH2 | Cl 2 chloro propane z Multiple alkyl groups are labeled with the Greek numerical prefixes such as di for two, tri for three, tetra for four, penta for five. If two alkyl groups are on the same carbon atom the numeral is repeated. CH3 | CH3 - C - CH2 -CH3 | CH3 2, 2 dimethyl butane Nomenclature Reference Chart IUPAC and Common Names Homologous series Alkanes CH4 .n =1 C2H6 n = 2 C3H8 n = 3 C4H10 ..n = 4 Alkenes n = 1 C2H4 n = 2 C3H6 n = 3 C4H8 n = 4 Alkynes n = 1 C2H2 n = 2 C3H4 n = 3 C4H6 n = 4 Volume 2 of 2 Condensed Structural Formula CnH2n+2[Paraffins] CH4 H3C CH3 H3C CH2 CH3 H3C CH2 CH2 CH3 CnH2n [Olefins] H2C = CH2 H3C.CH = CH2 H3C.CH2.CH = CH2 H3C.CH = CH CH3 CnH2n 2 HC CH H3C C CH H3C CH2 C CH H3C C C CH3 Functional Group Root Word Primary Suffix Secondar y Suffix Meth Eth Prop But >C=C< Double bond C C Triple bond Ane Ane Ane Ane Eth Prop But But ENe Ene Ene Ene Eth Prop But But Yne Yne Yne Yne IUPAC Name Trivial Or Common Name Methane Ethane Propane Butane Methane Ethane Propane Butane Ethene Propene 1 Butene 2 Butene Ethylen Propylene 1 Butylene 2 Butylene Ethyne Propyne 1 Butyne 2 Butyne Acetylene Methyl acetylene Ethyl acetylene Dimethyl acetylene Universal Tutorials X ICSE Chemistry 55 56 Homologous series Alcohols CH3OH n = 1 C2H5OH n = 2 C3H7OH n = 3 Aldehydes HCHO n =1 CH3CHO n = 2 C2H5CHO n=3 Carboxyl Acids HCOOH n = 1 CH3COOH..n=2 C2H5COOH.n=3 Alkyl Halides CH3Cl n = 1 C2H5Br n = 2 Ketones .n = 3 Ether .n = 2 Condensed Structural Formula CnH2n+ 1OH H3C OH H3C CH2 OH H3C CH2 CH2 OH CnH2nO H CHO H3C CHO H3C CH2 CHO CnH2n O2 H COOH H3C COOH H3C CH2 COOH CnH2n+ 1 X [X = F, Cl, Br,I] H3C Cl H3C CH2 Br CnH2n O H3C CO CH3 Functional Group Meth Eth Prop OH Hydroxyl .. H ...| C=O Aldehyde OH | C=O Carboxyl Halo [halides] F, Cl, Br, I, Ketonic O || C Alkoxy | | C O C | | CnH2n+2 O H3C O CH3 Root Word Primary Suffix Secondar y Suffix IUPAC Name Ane Ane Ane ol ol ol Methanol Ethanol 1 Propanol Trivial Or Common Name [Monohydric alcohols] Methyl alcohol Ethyl alcohol n Propyl alcohol Meth Eth Prop Ane Ane Ane al al al Methananl Ethanal Propanal Formaldehyde Acetaldehyde Propionaldehyde Meth Eth Prop Ane Ane Ane oic acid oic acid oic acid Methanoic acid Ethanoic acid Propanioc acid Formic acid Acetic acid Propionic acid Meth Eth Ane Ane Chloro Bromo Chloromethane Bromo Ethane Methyl Chloride Ethyl bromide Prop Ane one Propanone Acetone Meth Ane methoxy Methoxy methane Dimethyl ether IUPAC names: Examples 1: 1 2 3 CH3 CH CH3 | CH3 Word Root Suffix Prefix IUPAC name : Prop : ane : 2 methyl : 2-methyl propane Examples 2: 1 2 H C=C H Word Root Suffix Prefix IUPAC name : Eth : ene : 1, 2-dibromo : 1, 2-dibromo ethene Word Root Suffix Prefix IUPAC name : Eth : ane : 1, 1, 2, 2-tetrachloro : 1, 1, 2, 2-tetrachloroethane Word Root Suffix Prefix IUPAC name : But : ane : 2, 3-dimenthyl : 2, 3-dimenthyl butane | | Br Br Examples 3: Cl Cl |1 |2 H C C H | Examples 4: 4 | Cl Cl 3 2 1 CH3 CH CH CH3 | | CH3 CH3 Examples 5: H H |1 | 2 3 4 H C C C C H | | H H Example 6: CH3 |3 6 5 4 2 1 CH3 CH2 CH2 CH CH2 CH3 3 methyl hexane 56 Word Root Suffix : But : yne Prefix :2 IUPAC name : But 2-yne Example 7: CH3 CH3 |3 |2 1 CH3 CH2 CH2 CH2 CH CH CH3 7 6 Universal Tutorials X ICSE Chemistry 5 4 2, 3 dimethyl heptane Volume 2 of 2 Chapter 12: Organic Chemistry 57 Example 8: CH3 | 6 5 4 3 2 1 CH3 CH2 CH2 C CH2 CH3 | CH3 Example 9: 4 3 2 1 CH3 CH = CH CH3 But 2 ene 3, 3 dimethyl hexane Example 10: 1 Example 11: 2 3 4 1 CH3 | CH3 2C Br | 3 CH3 5 CH3 CH = C CH2 CH3 | CH3 4 methylpent 2 ene 2 bromo 2 methylpropane Example 12: 4 Example 13: 3 2 CH3 |2 1 CH3 CH CH2OH 1 CH3 CH2 CH2 CH2OH 3 Butan 1 ol 2 methyl propan 1 01 Example 14: Example 15: CH3 C2H5 |4 3 |2 5 1 CH3 C CH2 CH CH2OH | CH3 2 1 CH2CHO |3 4 5 CH3 CH2 CHO Pentane 1 5 dial 2 ethyl 4, 4 dimethyl pentan 1 ol Example 16: Example 17: O ||2 3 1 4 5 CH3 C CH2 CH2 CH3 C2H5 | 4 3 2 1 CH3 CH2 CH COOH pentan 2 one 2 ethyl butan 1 oic acid Writing Structural Formula From IUPAC name: Write the number of carbon atoms according to the word root (carbon skeleton). Number the carbon atoms from any end. According to the suffix ane, ene or yne position the bond is specified in the parent chain. Attach the substituent or functional group at the mentioned carbon atom. Satisfy the four valencies of carbon atom by attaching hydrogen atoms. Example: 2 Bromo 4 methyl pent 2 ene z Write the carbon atoms of the chain, C C C C C 2 3 4 5 z Number it 1 C C C C C z Locate the suffix z 2 3 Attach substituent 1 C C=C | Br z Satisfy valencies Volume 2 of 2 1 2 3 4 5 C C=C C C 4 5 C C | CH3 CH3 C = CH CH CH3 | | Br CH3 Universal Tutorials X ICSE Chemistry 57 58 12B Alkanes: Alkanes are hydrocarbons in which all the linkages between the carbon atoms are single covalent bonds. These compounds are known as saturated hydrocarbons since all the four valencies of carbon are fully satisfied in the formula CnH2n+2 by a single bond. Homologous series of alkanes: Name Methane Ethane Propane Normal butane Isobutane Molecular formula Abbreviated formula Structural formula CH4 H | H C H | H CH4 C2H6 H H | | H C C H | | H H CH3 CH3 C3H8 H H H | | | H C C C H | | | H H H CH3 CH2 CH3 C4H10 H H H H | | | | H C C C C H | | | | H H H H CH3 CH2 CH2 CH3 C4H10 H H H | | | H C C C H | | H H H C H | H CH3 CH CH3 | CH3 Sources of alkanes: z z 58 The principle sources of alkanes are natural gas and petroleum. Natural gas contains mainly methane with smaller amounts of ethane, propane and butane. Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry 59 Isomerism in alkanes i.e. single bond hydrocarbons: z Alkanes with more than three carbon atoms form isomers. Examples: Isomers of butane (C4H10): z Butane has four carbon atoms. These four carbon atoms can be arranged in two distinct ways. Therefore, there are two isomers of butane. H H H H | | | | H C C C C H | | | | H H H H n butane (C4H10), where n stands for normal IUPAC Name: Butane H H H | | | H C C C H | | H H H C H | H Iso-butane (C4H10) IUPAC Name : 2 Methyl propane Isomers of pentane (C5H12): z Pentane has five carbon atoms, which can be arranged in three different ways. Therefore pentane can form three isomers. H H H H H | | | | | H C C C C C H | | | | | H H H H H Common Name: n-pentane [C5H12] IUPAC Name: Pentane [ n , means no carbon atom is attached to more than two carbon atoms] CH3 | CH3 CH CH2 CH3 Common Name: isopentane [C5H12] IUPAC Name: 2-methyl butane [ iso , i.e. at least one carbon atom is attached to three other carbon atoms] CH3 | CH3 C CH3 | CH3 Common Name: neo-pentane [C5H12 IUPAC Name: 2, 2 dimethyl propane [ neo , i.e. at least one carbon atom is attached to four other carbon atoms]. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 59 60 Metha ane and Ethane: E Occ currence of methan ne and eth hane: M Methane (Ma arsh gas): Marsh gas is forme ed at the bottom of mars shes due to the fermenta ation of cellu ulose by a al type of bac cteria. specia It is als so present in n the air exha aled by animals whose fo ood contains cellulose. It is co ontained in in ntestinal gase es and in the e blood of animals and hu uman beings s. Methane is produc ced also by dry distillation n of wood, pe eat and coal. Ethane: It occurs to t the extent of 10 20 percent p along gwith methan ne. S Structure of f methane: The methane mole ecule is three e dimensiona al. The four outer o electron ns in the car rbon atom move as far apart t from each other as possible, bec cause electro ons repel ea ach other (remem mber that pa articles with similar s charge always rep pel each othe er). It is a fac ct that the electro ons will hav ve the grea atest distanc ce between themselves s when the e carbonhydrog gen bonds ar re in the shape of a tetrah hedron. H H | or H C H H C H | H H Electron dot d formula Struct tural formula Lab boratory preparatio p n of methane: R Reactants: Sodium m ethanoate (sodium ace etate) and so oda lime. (Soda lime is in th he form of a white porous mass or granules. It is s a mixture of o sodium hydrox xide and calc cium oxide). P Procedure: A mixt ture of sodium ehtanoa ate (sodium acetate) and so oda lime is ta aken in a har rd glass test tube and heated d with a Buns sen flame. Soda lime is (NaOH + CaO) R Reaction: CaO CH3CO OONa + NaO OH Na2CO3 + CH C 4 300 C C Collection: The ga as evolved is s collected by b downward d displaceme ent of water s since it is on nly slightly soluble e in water an nd is lighter th han air. Lab boratory preparatio p n of ethan ne: R Reactants: 60 Sodium m acetate or sodium prop pionate and soda s lime. (N NaOH + CaO O) U Universal Tuto orials X ICS SE Chemistr ry Volu ume 2 of 2 Chapter 12: Organic Chemistry 61 Procedure: A mixture of sodium propionate and soda lime is taken in a boiling tube and heated with a Bunsen flame. Reaction: CaO C2H5COONa + NaOH Na2CO3 + C2H6 300 C Collection: The gas evolved is collected by downward displacement of water. Other methods of preparation of methane and ethane: z When water is added at room temperature to aluminium carbide, methane is prepared. z Al4C3 + 12H2O 3CH4 + 4Al(OH)3 By the reduction of iodomethane (methyl iodide) or (ethyl bromide) at ordinary temperature by nascent hydrogen. CH3I + 2[H] CH4 + HI Iodomethane z C2H5Br + 2[H] C2H6 + HBr [H] is produced by the action of Zn and dil. HCl Catalytic hydrogenation of alkene and alkyne Ni H2C = CH2 + H2 H3C CH3 250 C z From alkyl halides Sodium metal in presence of dry ether on warming with methyl iodide or methyl bromide produces ethane. dry 2CH3I + 2Na H3C CH3 + 2NaI ether This reaction is referred to as Wurtz reaction. Physical properties: Methane: It is a colourless and an odourless gas. Its melting point is 183 C and its boiling point is 162 C. It is negligibly soluble in water and soluble in organic solvents. Like carbon dioxide molecules, methane molecules also absorb outgoing heat radiation from the earth and thus contribute to green house effect. Ethane: Volume 2 of 2 It is a colourless, odourless, tasteless and non-poisonous gas. Its b.p. is 89 C and its m.p. is 172 C. It is sparingly soluble in water but wholly soluble in organic solvents like alcohols, acetone and ether. Universal Tutorials X ICSE Chemistry 61 62 Chemical properties: Substitution reaction: Reaction with halogens: Alkanes react with chlorine, bromine or iodine in the presence of sunlight or ultraviolet light to give halogen substituted products known as alkyl halides, containing one or more halogen atoms. diffused sunlight CH3Cl + HCl CH4 + Cl2 or 600K diffused sunlight C2H5Cl + HCl C2H6 + Cl2 or 600K Reaction with oxygen: Methane and ethane burn in air with a bluish non sooty flame to form carbon dioxide and water vapour, large amount of heat is also given out. Thus, they are good gaseous fuels. During combustion, due to the low carbon content in methane and ethane, they fully get oxidised to carbon dioxide so they burn with a non sooty flame. CH4 + 2O2 CO2 + 2H2O 2C2H6 + 7O2 4CO2 + 6H2O Insufficient supply of air: z When alkanes burn in an insufficient supply of air (oxygen), they form carbon monoxide and water. 2CH4 + 3O2 2CO + 4H2O 2C2H6 + 5O2 4CO + 6H2O CH4 + O2 C + 2H2O (with still less oxygen) Decomposition of alkanes: Cracking or pyrolysis When decomposition of alkanes occurs by heat in the absence of air, large alkane molecules are broken down into a mixture of smaller molecules. This is known as cracking or pyrolysis. 400 600 C C5H12 C3H8 + C2H4 pentane propane ethane Catalytic oxidation of alkane: z On controlled oxidation or catalytic oxidation, alkanes give alcohols or aldehydes or carboxiylic acids, When a mixture of methane and oxygen in the ratio 9:1 by volume is compressed to about 120 atm and passed over copper tubes at 475 K, methyl alcohol is formed. 2CH4 + O2 2CH3OH 475K Cu tube When a mixture of methane and oxygen is passed through heated molybdenum oxide (MoO), the mixture is oxidized to formaldehyde. MoO CH4 + O2 HCHO + H2O 62 When a manganese based catalyst is used at 100 C, methane can be oxidized to formic acid. 2CH4 + 3O2 2HCOOH + 2H2O Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry 63 Slow combustion: z When methane or ethane is treated with oxidizing agent like K2Cr2O7 at high pressure and comparatively low temperature. [O ] [O ] [O ] K 2Cr2O7 K 2Cr2O7 K 2Cr2O7 Alcohol Aldehyde Carboxylic acid carbon dioxide & water vapour Alkane CH4 Methane [O ] [O ] [O ] [O ] CH3OH HCHO CO2 + H2O HCOOH Methyl alcohol Formaldehyde Formic acid Uses: Methane: z Methane is a source of carbon monoxide and hydrogen. z It is used in the preparation of ethyne (acetylene), methanal (formaldehyde), methanol, chloromethane and tetrachloromethane (carbon tetrachloride). z It is employed as a domestic fuel. Ethane: z Ethane is used in the preparation of ethene, ethanol, ethanal (acetaldehyde) and ethanoic acid (acetic acid). z It forms ethyl chloride, which is used to make tetraethyl lead. z It is also a good fuel. 12C Alkenes: Alkenes are also called olefins because lower members form oily products when treated with chlorine or bromine. They form a homologous series of the general formula CnH2n. They are unsaturated aliphatic hydrocarbons which contain one double bond. Molecular formula C2H4 Condensed formula H H | | H C=C H CH2 = CH2 C3H6 CH3 CH = CH2 C4H8 Structural formula CH3 CH2 CH =CH2 H H H | | | H C C=C H | H H H H H | | | | H C C C = C H | | H H Trivial name (Common name) IUPAC name Ethylene Ethene Propylene Propene Butylene Butene Alkene are unsaturated aliphatic hydrocarbons that contain one double bond. Isomers in alkenes: z z Alkenes with 4 or more than 4 carbon atoms can form isomers. For example: Butene has three isomers: Volume 2 of 2 Universal Tutorials X ICSE Chemistry 63 64 CH3CH H2CH = CH2 Bute-1-e ene CH3CH H = CHCH3 CH2 = C CH3 | C 3 CH But -2-ene 2-methyl propene p ypes of isome erism shown n by Alkenes Ty i) Chain Isom merism: Example: CH 3 C 3CH2CH = CH2 CH | CH H3 C = CH2 2-m methyl propene 1- butene ii) Position iso omerism: Example CH3CH2CH H = CH2 CH H3CH = CHC CH3 1-butene 2-butene Eth hene (Ethy ylene) C2H4: z It is the first member of the alken ne series. It is i present in natural gas s. In small am mounts, it occurs as s a plant horm mone and is responsible for the ripening of fruits. Str ructure of ethene: z Each carb bon atom of ethene is attached to tw wo hydrogen n atoms by s single covale ent bonds and to an nother carbo on atom by a double covalent c bon nd. There ar re four C H single covalent bonds b and on ne C = C dou uble covalen nt bond. Prepa aration of f ethene (ethylene ( e): Deh hydration of ethyl alcohol: a R Reactants: Ethano ol and conc. sulphuric ac cid. P Procedure: Take one o part of ethyl e alcohol in a flask. Add two pa arts of conc centrated sul lphuric acid and heat gradually g to about 160 C. Ethylene is evolve ed. It is collected by downw ward displac cement of water w (add some s alumin nium sulpha ate to the water in order to avoid a frothing). R Reaction: CH3CH H2 OH + H2SO S 4 CH3CH2HSO4 + H2O (Eth hanol) 64 (Ethy yl hydrogen sulphate) H2SO 4 e excess CH3CH H2 HSO4 CH 2 160 C Ethene = CH H2 + H2SO4 U Universal Tuto orials X ICS SE Chemistr ry Volu ume 2 of 2 Chapter 12: Organic Chemistry 65 Collection: The gas is collected by downward displacement of water because: i) It is an inflammable gas. ii) It is insoluble in water. By dehydration: Industrial preparation By passing ethanol vapours through the tube containing alumina (Al2O3) at 300 C. Al 2O3 C2H5OH C2H4 + H2O 300 C Dehydrohalogenation C2H5Cl + KOH (alc.) C2H4 + KCl + H2O C2H5Br + KOH (alc.) C2H4 + KBr + H2O C2H4 + KI + H2O C2H5I + KOH (alc.) Properties of Alkenes: Physical properties: z Ethene is a colourless and inflammable gas with a peculiar odour (faint sweetish smell). z Its boiling point is 102 C. and melting point is 169 C. It is sparingly soluble in water but highly soluble in organic solvents like alcohol, ether and chloroform. It produces an anaesthetic effect upon inhalation. z z Chemical properties: Addition reaction: z Double bond of alkenes is a combination of two single covalent bonds, the weaker bond out of these two bonds breaks up, each carbon atom has one free electron which then forms a single bond with the reacting reagent. This results in the formation of saturated products. -C = C +AB C C A B Addition of hydrogen (hydrogenation): When ethene and hydrogen are passed over finely divided catalysts such as platinum or palladium at ordinary temperature or nickel at 200 C, the two atoms of hydrogen molecule are added to the unsaturated molecule, which thus becomes a saturated one. 200o C C2H4 + H2 C2H6 Ni Ethene Ethane Addition of halogens (halogenation): reaction with fluorine is explosive hence the compound formed is not stable. Chlorine, bromine and iodine are added to the double bond of ethene (ethylene) at room temperature to form saturated ethylene chloride, ethylene dibromide and ethylene di iodide. CCl 4 CH2 = CH2 + Cl2 CH2 CH2 Ethene | I Cl Cl 1, 2-dichloro ethane (ethylenedichloride) Volume 2 of 2 Universal Tutorials X ICSE Chemistry 65 66 CH2 = CH2 + Br2 CH2 CH2 Ethene | | Br Br 1, 2-dibromo ethane (ethylenedibromide) Bromine solution in CCl4 has an orange colour. When added dropwise to ethene, the orange colour of bromine disappears due to the formation of the colourless ethylene bromide. C2H4 + I2 C2H4I2 1, 2-di iodoethane (ethylene iodide) Reaction with iodine is very slow and ethylene iodide formed is unstable. It eliminates the iodine readily and regenerates the ethene. Brown colour of bromine discharged serves as a test for unsaturation. Addition of water: A water molecule gets added to alkenes in the presence of acids (e.g. sulphuric acid) to form alcohols. H+ C2H5OH. CH2 = CH2 + H2O Addition of HCl: When ethene gas is treated with HCl, chloroethane is formed. CH2 = CH2 + HCl(aq) CH3 CH2Cl Ethene Ethyl chloride (chloroethane) If choloroethane is treated with potassium hydroxide solution, ethanol is formed, HC3CH2Cl + KOH CH3CH2OH + KCl Reaction with ozone (ozonolysis): When a stream of ozone is passed through a solution of ethene in ether, ethene ozonide is formed. H2C = CH2 + O3 H2C O CH2 Ethene Ozone O O Ethene ozonide Polymerization: When two or more molecules of the same compound associate to form a bigger molecule, the reaction is called polymerization. high temperature nH2C = CH2 [ H2C CH2 ]n Polymerisation Ethene Polyethene high pressure catalyst Oxidation: Ethene is oxidized with alkaline KMnO4 at room temperature. Cold alkaline H2C CH2 H2C = CH2 + H OH + [O] KMnO4 so ln . Ethene OH OH 1, 2 Ethanediol (Ethylene glycol) Purple colour of KMnO4 decolourises Combustion of ethene: Ethene burns in air with a sooty flame producing a large amount of heat. However, if the supply of air is in excess, it burns with a pale blue flame to form carbon dioxide and water with the liberation of a large amount of heat. CH2 = CH2 + 3O2 2CO2 + 2H2O + Heat 66 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry 67 Uses of ethene: z z z z z z Ethene is used in making polythene. It is converted into ethanol which is used as a starting material for other products, mainly cosmetics and toiletry preparations. It is used for ripening of fruits. It is used in making epoxyethane (used in the manufacture of detergents). It is used for producing oxy-ethylene flame, which is used for cutting and welding metals. It is used in the manufacture of synthetic chemicals. 12D Alkynes: The aliphatic hydrocarbons that contain a triple bond ( C C ) i.e. acetylenic bond between two carbon atoms are known as alkynes. They form a homologous series with the general formula CnH2n 2 Molecular formula Condensed formula Structural formula Trivial name IUPAC name of the compound CH CH C3H4 H C C H Acetylene Ethyne CH3 C CH C2H2 H | H C C C H | H Allylene Propyne Crotonylene Butyne CH3 CH2 C CH C4H6 H H | | H C C C H | | H H Sources of alkynes: Natural gas and petroleum. Isomers in alkynes: Alkynes with four or more than four carbon atoms can form isomers. Alkynes show position isomerism as well as chain isomerism. For Example: Butyne: It shows position isomerism. i) CH3 CH2 C CH IUPAC Name: But-1-yne ii) CH3 C C CH3 IUPAC Name: But 2-yne Ethyne (Acetylene): Molecular formula: C2H2 z z Ethyne is the first member of the alkyne series. Ethyne being an unsaturated hydrocarbon, is not found in free state. Sources: Traces of ethyne are present in coal gas and in gases obtained by the decomposition of certain complex organic compounds. It is obtained by cracking of alkanes from various fractions of petroleum. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 67 68 Str ructure of ethyne (acetylene): : z Each carb bon atom in acetylene is s attached to o one hydrog gen atom by single covalent bond and to ano other carbon n atom by a triple t covalen nt bond. H C C H Str ructural formula HxC CxH Ele ectron dot for rmula Lab boratory preparatio p n of ethyn ne (acetyle ene): z z Reactants: Water and d calcium carbide. Procedur re: Take a fe ew pieces of f calcium car rbide water th hrough the thistle funnel. Calcium carbide re eacts with wa ater to produce acetylene e gas. The re eaction is exo othermic. C H OH ||| + Ca (OH)2 Ca ||| + C CH CH H OH Reaction: CaC2 + 2H 2 2O Ca(OH)2 Calcium carbid de z z + Calc cium hydroxide C2H2 acetylen ne Collection: The gas is collected by b downward d displaceme ent of water, since it is ins soluble in water. Purification: Impuriti ies like pho osphine, hyd drogen sulph hide, ammo onia and ars senic are formed along with ace etylene. But on passing through t wate er, all impurit ties except phosphine p are absor rbed, phosph hine is absorb bed by passi ing through acidified a pota assium dichr romate. Oth her metho ods of prep paration of o alkynes: z From met thane or natu ural gas (pyro olysis). When methane is heated arou und 1500 C in an electric c arc followe ed by sudden n cooling, ethyne e is formed. 1500 C 2CH4 H2 CH CH + 3H Methane e z Ethyne From 1, 2 dibromoeth 2 hane (Ethylen ne dibromide e). When 1, 2 dibr romoethane (ethylene dibromide) is boiled with h alcoholic potassium p hydrox xide, ethyne is formed. a alcohol CH2Br r + 2KOH CH + 2KBr + 2H2O boil CH2Br CH (alcoholic) (Ethyne) Phy ysical pro operties: z Acetylene e is a colourl less gas with h ether like odour when it is pure (th he one prepa ared from calcium carbide has garlic g odour due d to the presence of tr races of pho osphine and hydrogen sulphide). . It is negligibly soluble in water but highly soluble s in or rganic solvents like ace etone and alcohol. It is lighter than air (V. .D. = 13). z It liquefies s at 84 C. z Its boiling point is 75 C. z z 68 U Universal Tuto orials X ICS SE Chemistr ry Volu ume 2 of 2 Chapter 12: Organic Chemistry 69 Chemical properties: Ethyne is a highly reactive compound because of the presence of triple bond between two carbon atoms. Oxidation of ethyne (combustion): z z Ethyne has more percentage of carbon content than alkanes and alkenes i.e. ethane and ethene. All the carbon particles in the flame do not get oxidised completely, so it burns with a sooty flame. 2CH CH + 5O2 4CO2 + 2H2O + Heat Ethyne burns in excess air with a brilliant white flame to form carbon dioxide and water vapour with the liberation of large amount of heat. Addition reactions: z Alkynes are unsaturated compounds, so they are associated with addition reactions, since triple bonds break up easily. The breaking up of a triple bond gives a product that is still unsaturated (double bond). Further breaking up of the double bond gives a saturated product. i) Addition of hydrogen (catalytic hydrogenation): z In the presence of nickel, platinum or palladium, ethyne first takes up two atoms of hydrogen to change to ethene, which further takes up two atoms of hydrogen to given ethane. First stage of reaction: Ni C2H2 + H2 C2H4 Ethyne Ethene Second stage: Ni C2H4 + H2 C2H6 Ethene Ethane Therefore, +H2 / Ni +H2 / Ni HC CH CH2 = CH2 CH3 CH3 Ethyne Ethene Ethane ii) Addition of halogen: Reaction with chlorine: +Cl 2 C2H2 +Cl 2 C2H2Cl4 C2H2Cl2 Ethyne (Acetylene) Acetylene dichloride (1,2dichloroethane) Acetylene tetrachloride (1,1,2,2 tetrachloro ethane) Reaction with bromine: +Br2 +Br2 C2H2Br2 C2H2Br4 C2H2 Ethyne (Acetylene) Acetylene dibromide Acetylene tetrabromide Reaction with iodine: CH CH + I2 ICH = CHI (1, 2, di iodoethene) Reaction with ozone: z O HC CH + O H C C H 3 Ethyne reacts with ozone at room temperature to | | produce acetylene ozonide. O O (Acetylene ozonide) Volume 2 of 2 Universal Tutorials X ICSE Chemistry 69 70 Uses of ethyne (acetylene): z for oxy-acetylene welding involving very high temperatures, these temperatures are obtained when ethyne burns in oxygen. z as an illuminant in oxyacetylene lamp. z for artificial ripening and preservation of fruits. z also for the manufacture of synthetic products like polymers, artificial rubber, oxalic acid etc. z for the manufacture of important organic compounds like acetaldehyde, acetic acid, plastic, rubber etc. Chemical Tests to distinguish between Alkanes, Alkenes, Alkenes and Alkynes: No. 1 Test On adding a few drops of bromine solution in carbon tetrachloride to the hydrocarbon On adding a few drops of alkaline potassium permanganate (purple colour) to the hydrocarbon 2 3 On adding a few drops of ammoniacal cuprous chloride to the hydrocarbon On adding ammoniacal Silver nitrate 4 Alkanes (Methane and ethane) Saturated compound No change is observed No change is observed Alkenes (Ethylene) Unsaturated compound The reddish brown colour of bromine solution gets decolorized The purple colour fades Alkynes (Acetylene) Unsaturated compound The reddish brown colour get decolorized The purple colour fades (Baeyer s test) CH CH + 4[O] Ethyne COOH alk . KMnO 4 | COOH Oxalic acid No change is observed No change is observed Red precipitate of copper acetylide is formed No observation No observation White precipitate of silver acetylide is formed 12E Alcohols: Alcohols are the hydroxy derivatives of alkanes. They are formed by replacing one hydrogen atom of the alkane by OH group. For example, methyl alcohol is derived from methane and ethyl alcohol from ethane. Alcohols can be monohydric which has one OH group attached to it. Homologous series of alcohols (General formula: CnH2n+1OH) Common Name Methyl alcohol Molecular formula CH3 OH Abbreviated formula CH3 OH Ethyl alcohol C2H5OH CH3 CH2 OH Propyl alcohol C3H7 OH CH3 CH2 CH2 OH 70 Structural formula H | H C O H | H H H | | H C C O H | | H H H H H | | | H C C C O H | | | H H H Universal Tutorials X ICSE Chemistry IUPAC Name Methanol Ethanol Propanol Volume 2 of 2 Chapter 12: Organic Chemistry Common Name 71 Molecular formula Butyl alcohol C4H9OH Abbreviated formula CH3 CH2 CH2 CH2 OH IUPAC Name Structural formula H H H H | | | | H C C C C O H | | | | H H H H Butanol Laboratory preparation: Alcohol can be prepared by the hydrolysis of haloalkanes (alkyl halides) with water or hot dilute alkali. boil RX + KOH ROH + KX boil C2H5OH + KCl Eg. C2H5Cl + KOH(aq) CH3Cl + KOH CH3OH + KCl Industrial method (large scale method): Ethanol: Hydrolysis of ethene: z When concentrated sulphuric acid is added to ethene at a temperature of 80 C and pressure 30 atm, ethyl hydrogen sulphate is produced. Ethyl hydrogen sulphate, on hydrolysis with boiling water, gives ethanol. 80o C C2H4 + H2SO4 C2H5HSO4 30 atm C2H5HSO4 + Ethyl hydrogen sulphate H2O C2H5OH + H2SO4 (boiling) Ethanol Fermentation of carbonhydrates: z Ethanol is prepared by the fermentation of sugar (molasses) by the enzymes invertase and zymase. invertase C6H12O6 + C6H12O6 C12H22O11 + H2 O fermentation Cane sugar zymase [ yeast ] C6H12O6 2C2H5OH + 2CO2 Glucose fermentation Ethanol Properties of alcohols: A Physical properties: z Nature: They are inflammable volatile liquids. z Boiling point: Their boiling point increases with an increase in molecular weight. Examples: CH3OH = 64.5 C; CH3CH2OH = 78.3 C z Solubility: They are soluble in water as well as in organic solvents. z Density: Ethanol is lighter than water as its density is 0.79 cm 3 at 293 K. z They are colourless and have a faint odour. z They are toxic. Example: methyl alcohol, if consumed, causes blindness and even death. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 71 72 Chemical properties: z Alcohols is a reactive class of compounds Combustion (Burning): z Alcohol burns readily in air producing carbon dioxide and water vapour. A lot of heat is produced during the combustion of alcohols. C2H5OH + 3O2 2CO2 + 3H2O Reaction with conc. sulphuric acid: z When concentrated sulphuric acid is added to ethyl alcohol and the mixture is heated upto 170 C, it causes dehydration of ethyl alcohol and ethene is produced. conc .H2SO4 CH2 = CH2 + H2O C2H5OH 170 C Ethyl alcohol Ethene If alcohol is in excess, then H2SO4 at 140 C dehydrates alcohol to give the respective ether. Reaction with oxidising agents: z Alcohols when reacting with oxidising agents like potassium dichromate and potassium permanganate in the presence of acid they first get converted into aldehydes and later change into respective acids. [O ] CH3OH HCHO Methyl alcohol [O ] + H2O HCOOH Formaldehyde Formic acid [O ] CH3CHO C2H5OH Ethyl alcohol [O ] CH3COOH + H2O Acetaldehyde (ethanol) Acetic acid (ethanoic acid) Reactions with acetic acid: z When alcohols react with acetic acid in the presence of conc.H2SO4 at high temperatures respective esters are produced, this process is known as esterification. CH3OH + CH3COOH CH3COOCH3 + H2O Methyl acetate C2H5OH + CH3COOH CH3COOC2H5 + H2O Ethyl acetate z Esters can be detected by their fruity smell (TEST) Reaction with sodium: z When sodium reacts with methyl and ethyl alcohols at room temperature, hydrogen is evolved with the formation of sodium methoxide and sodium ethoxide respectively. 2CH3OH + 2Na 2CH3ONa + H2; Sodium methoxide 2C2H5OH + 2Na 2C2H5ONa + H2 Dehydration with conc. sulphuric acid: z When concentrated sulphuric acid is added to ethyl alcohol and the mixture is heated upto 170 C, it causes dehydration of ethyl alcohol to give ethene. conc.H SO 2 4 C2H5OH CH2 = CH2 + H2O 170 C Ethyl alcohol Ethene Uses of alcohol: z z z 72 It is a good solvent for gums and resins. It is used in thermometers due to its low freezing point. It is used in the manufacture of chemicals and synthetic products like dyes, perfumes, antiseptics, preservatives etc. Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry z z 73 Ethyl alcohol is used in alcoholic drinks (beverages) like whisky, wine and beer. One of its products, chloroform, is used as an anaesthetic. Preparation of absolute alcohol: z z The alcohol obtained by distillation is 95% pure. It forms a constant boiling mixture of 5% water and 95% ethanol. Absolute alcohol may be obtained by distilling moist alcohol with benzene (an organic solvent). The mixture of water and benzene distills off and anhydrous alcohol is left behind. Spurious alcohol, though impure, can be used as a solvent for paints and varnishes. Denatured alcohol or methylated spirit: z Ethyl alcohol is a part of drinking beverages and is also a widely used solvent in industries. In order to make it undrinkable, certain poisonous substances like pyridine, methyl alcohol and copper sulphate are added to it. Methylated spirit or denatured alcohol is ethyl alcohol, to which 5% methyl alcohol, a coloured dye and some pyridine is added. 12F Carboxylic Acids: Carboxylic Acids: An organic compound containing the carboxyl group (COOH) is known as carboxylic acid and they possess acid properties. General formula: CnH2n+1COOH (or RCOOH) Functional group: O C OH An organic compound may contain one or more of these groups. Those which contain one COOH group are called monocarboxylic acid. Those which contain two COOH group are called dicarboxylic acids. For example: HOOC COOH Oxalic acid IUPAC Name: Ethanedioic acid Monocarboxylic acids: Those organic acids which have one carboxyl group linked to a hydrocarbon radical. O || H C OH Formic acid O || CH3 C OH O || CH3 CH2 C OH Acetic acid Propionic acid IUPAC name: It is given by replacing e of the corresponding alkane by oic acid. Homologous series of monocarboxylic acid Gen formula CnH2n+1COOH Formula Common name IUPAC name O || Formic acid Methanoic acid H C OH O || CH3 C OH Volume 2 of 2 Acetic acid Ethanoic acid Universal Tutorials X ICSE Chemistry 73 74 Formula Common name IUPAC name O || CH3 CH2 C OH Propionic acid Propanoic acid Butyric acid Butanoic acid O || CH3 CH2 CH2 C OH Acetic acid CH3 COOH: Structural formula: H | H C C | H O OH Vinegar is a dilute (4 5 percent) solution of acetic acid. Occurrence: The acid occurs in free state in many fruits and as esters in a number of essential oils. Lab preparation: Acetic acid can be prepared in the lab by oxidation of ethyl alcohol (or acetaldehyde) with potassium dichromate or sodium dichromate and moderate concentrated sulphuric acid. [O] [O] CH3CH2OH CH3CHO CH3COOH ethanol ethanal ethanoic acid [O] CH3CHO CH3COOH Manufacture: From acetylene: Acetylene is first converted into acetaldehyde by passing through 40% H2SO4 at 60 C in the presence of 1% H2SO4 (catalyst). H SO ( dil.) 2 4 CH3COOH C2H2 + H2O HgSO4 The acetaldehyde is oxidized to acetic acid when a mixture of acetaldehyde vapours are heated to 70 C. 2CH3CHO + O2 2CH3COOH From ethanol: Acetic acid can also be prepared by passing alcohol vapours over platinum black as catalyst at 300 C in presence of oxygen. 300 o pt CH3COOH + H2O C2H5OH + O2 Physical properties: Physical state: Pure acetic acid is a colourless liquid. Odour: Characteristic pungent smell. Boiling point: 74 It boils at 118 C. Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry 75 Melting point: The anhydrous acid on cooling forms crystalline mass resembling ice; melting point 17 C and for this reason it is called glacial acetic acid. Nature: It is hygroscopic liquid, sp. gr. at 0 C is 1.08. Solubility: It is miscible with water, alcohol and ether in all proportions. Chemical properties: It is a weak acid, hence z Turns blue litmus red. z Reacts with active metals (i.e. Zn and Mg) evolving hydrogen. 2CH3COOH + Mg (CH3COO)2 Mg + H2 Accetic acid z Magnesium acetate Forms salt and water with bases Acid + CH3COOH + Base NaOH Acetic acid Salt CH3COONa + + Water H2O Sod. acetate z Liberates carbon dioxide with carbonates or hydrogen carbonates. z 2CH3COOH + Na2CO3 2CH3COONa + H2O + CO2 Formation of ester (Esterification): Acetic acid reacts reversibly with alcohols in presence of conc. H2SO4 forming esters. H SO 2 4 CH3CO OH + HOC2H5 CH3COOC2H5 + H2O acetic acid ethanol ethyl acetate z Conversion to acetylchloride. z CH3COOH + PCl5 CH3COCl + POCl3 + HCl Formation of acetic anhydride on heating with phosphorus pentoxide, it looses water molecule. (CH3CO)2O + H2O 2CH3COOH P2 O5 z Reduction: A strong reducing agent such as lithum aluminium hydride (LiAlH4) will reduce acetic acid to ethanol. CH3COOH + 4[H] C2H5OH + H2O Test: On adding acetic acid to carbonates and bicarbonates, carbon dioxide is evolved. When warmed with ethyl alcohol and conc. sulphuric acid, a pleasant fruity smell of ethyl acetate is produced. On adding neutral iron (III) chloride, wine red colour is produced. Acetic acid is used: As a solvent for resins, cellulose etc. As a laboratory reagent. As vinegar. In medicines. In the production of dyes, perfumes, esters etc. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 75 76 For coagulating rubber from latex. For the manufacture of cellulose acetate which is used for making packaging materials, varnishes, rayons etc. PREVIOUS YEARS BOARD QUESTIONS: Year 2012: 1) Give the structural formula for the following: i) Methanoic acid ii) Ethanol iii) Ethyne iv) Acetone v) 2 methyl propane 2) From the following organic compounds given below, choose one compound in each case which relates to the description (i) to (iv): i) An unsaturated hydrocarbon used for welding purposes. ii) An organic compound whose functional group is carboxyl. iii) A hydrocarbon which an catalytic hydrogenation gives a saturated hydrocarbon. iv) A solvent used as a thermometric liquid. 3) i) Why is pure acetic acid known as glacial acetic acid? ii) Give a chemical equation for the reaction between ethyl alcohol and acetic acid. Year 2010: 1) Draw the structural formula for each of the following: [2] i) Ethanoic acid ii) But 2 yne 2) Compound A is bubbled through bromine dissolved in carbon tetrachloride and the product is CH2Br CH2Br. [5] Br / CCl 2 4 A CH2Br CH2Br i) Draw the structural formula of A. ii) What type of reaction has A undergone? iii) What is your observation? iv) Name (not formula) the compound formed when steam reacts with A in the presence of phosphoric acid. v) What is the procedure for converting the product of (iv) back to A? Year 2009: 1) Methane is the first member of alkane, when it is treated with excess of chlorine in the presence of diffused sunlight forms carbon tetrachloride. Draw the appropriate structural formula of carbon tetrachloride and state the type of bond present in it. [4] 2) Fill in the blanks with the correct words from the brackets: [4] Generally ionic compounds exist in (i) __________ (solid/ liquid/ gas) state. Melting and boiling points of covalent compounds are generally (ii) _________ (low/ high). The general formula for alkane is (iii) _______ (CnH2n/ CnH2n 2/ CnH2n+2). For alkynes the general formula is (iv) _______ (CnH2n/ CnH2n 2/ CnH2n+2). 3) Give chemical equation for: i) The laboratory preparation of methane from sodium acetate. ii) The reaction of one mole of ethane with one mole of chlorine gas. iii) The preparation of ethyne from 1, 2 dibromoethane. 4) State how the following conversions can be carried out: i) Ethyl chloride to Ethyl alcohol. ii) Ethyl chloride to Ethene. iii) Ethene to Ethyl alcohol. iv) Ethyl alcohol to Ethene. 76 Universal Tutorials X ICSE Chemistry [3] [4] Volume 2 of 2 Chapter 12: Organic Chemistry 77 5) i) Define isomerism. [2] ii) Give the IUPAC name of the isomer of C4H10 which has a branched chain. Year 2008: 1) Select the correct answer from the choices A, B, C, D which are given: The formation of 1, 2-dibromoethane from ethene and bromine is an example of [1] A) Substitution B) Dehydration C) Dehydrohalogenation D) Addition 2) Name the organic compound prepared each of the following reactions: i) C2H5COONa + NaOH ii) CH3 + 2H iv) CaC2 + 2H2O iii) C2H5Br + KOH (alcoholic solution) 3) Identify the following substance: [1] Liquid (E) can be dehydrated to produce ethene. 4) Write the equation for the following reactions. [3] i) Calcium carbide and water ii) Ethene and water (steam) iii) Bromoethane and an aqueous solution of sodium hydroxide. 5) What is the term defined below? [1] A reaction in which the hydrogen of an alkane is replaced by another element like chlorine 6) a) Distinguish between the saturated hydrocarbon ethane and the unsaturated hydrocarbon ethene by drawing their structural formulae. [2] b) Addition reactions and substitution reactions are types of organic reactions. Which type of reaction is shown by [2] i) Ethane? ii) Ethene? c) i) Write equation for the complete combustion of ethane. ii) Using appropriate catalysts, ethane can be oxidized to an alcohol, an aldehyde and an acid. Name the alcohol, aldehyde and acid formed when ethane is oxidized. [4] d) i) Why pure acetic acid is known as glacial acetic acid? ii) What type of compound is formed by the reaction between acetic acid and an alcohol? [2] Year 2007: 1) Give the IUPAC names of the following compounds numbered (i) to (v). The IUPAC names of the compounds on the left are to guide you into giving the correct IUPAC names of the compounds on the right. [5] H H H H | | | | H C C C H H C C=C | | | H H H Propene (i) ________ H H | | H C C | | H H H H H | | | C C C H | | | H O H H Pentan 2 ol Volume 2 of 2 H H | | H C C | | H H H H H | | | C C C H | | | O H H H (ii) ______ Universal Tutorials X ICSE Chemistry 77 78 H | H C H H H | | H C C C H | | H H H C H | H 2, 2 Dimethylpropane H H O | | || H C C C | | | H H OH Propanoic acid H H | | H C C H | | Br Br H H H | | | H C C C H | | H H H C H | H (iii) ________ H O | || H C C | | H OH (iv) ______ H H | | H C C H | | Cl Cl 1, 2 Dibromoethane (v) __________ 2) Copy and complete the following table which relates to three homologous series of hydrocarbons: [10] General Formula CnH2n C2n 2 CnH2n+2 IUPAC name of the homologous series Characteristics Single bond IUPAC name of the first member of the series Type of reaction with chlorine Addition 3) Name the type of chemical reaction by which C2Br6 can be prepared from ethane. [1] Year 2006: 1) Write balanced chemical equations for the following reactions: i) Ethane and oxygen in the presence of molybdenum oxide. ii) Preparation of methane from anhydrous sodium ethanoate (Sodium acetate). [3] iii) Heating ethanol at 443 K (170 C) in the presence of concentrated sulphuric acid. 2) a) Give the correct IUPAC name and the functional group for each of the compounds whose structural formulae are given below: H H O | | || i) H C C C H | | H H ii) H H O | | || H C C C OH | | H H b) i) Write the equation for the preparation of carbon tetrachloride from Methane. ii) Draw the structural formulae of Ethyne. iii) How is the structure of alkynes different from that of alkenes 78 Universal Tutorials X ICSE Chemistry [3] Volume 2 of 2 Chapter 12: Organic Chemistry 79 c) Fill in the blanks with the words from the brackets: Alkenes are the (i) __________ (analogous/homologous) series of (ii) _________ (saturated/ unsaturated) hydrocarbon. They differ from alkanes due to the presence of (iii) ______ (double/ single) bonds. Alkenes mainly undergo (iv) ______ (addition/ substitution) reactions. 3) i) Draw the structural formulae of the two isomers of butane, Give the correct IUPAC name of each isomer. ii) State one use of acetylene. [3] Year 2005: 1) a) Draw the structural formula of a compound with two carbon atoms in each of the following cases: i) An alkane with a carbon to carbon single bond. ii) An alcohol containing two carbon atoms. iii) An unsaturated hydrocarbon with a carbon to carbon triple bond. [3] b) Ethane, Ethene, Ethanoic acid, Ethyne, Ethanol From the box given above, name : i) The compound with OH as the part of its structure. ii) The compound with COOH as the part of its structure. iii) Homologue of homologous series with general formula C2H2n. [3] c) Write the equations for the following laboratory preparations: i) Ethane from sodium propionate ii) Ethene from iodoethane iii) Ethyne from calcium carbide iv) Methanol from iodomethane [4] 2) Define catenation. CLASS WORK EXERCISE: Organic Compounds: 1) What are hydrocarbons? How are they classified? Compare saturated and unsaturated hydrocarbons? 2) Give the reason for the existence of too many organic compounds? 3) a) Why are organic compounds studied as a separate branch of chemistry? b) Name the various sources of organic compounds. 4) a) What is a homologous series? b) What is the difference in the molecular formula of any two adjacent homologues? i) in terms of molecular mass, ii) in terms of number and kinds of atoms per molecule? 5) Explain isomerism with an example. State two main causes of isomerism 6) a) By using general formula for alkanes, write the formula of its sixth member. b) Write the condensed formula of the above compounds and predict its IUPAC name. 7) Write any four properties of organic compounds that distinguishes them from inorganic compounds. 8) Give the name of one member of each of the following a) saturated hydrocarbons, b) unsaturated hydrocarbons. 9) Give the names and structural formulae of the first three members of homologous series of alkanes. 10) Write the IUPAC name of: H H H CH3 | | | | a) CH3 C CH3 b) CH3 CH CH2 CH3 c) H C = C C H | | | CH3 H CH3 Volume 2 of 2 Universal Tutorials X ICSE Chemistry 79 80 11) a) What is an alkyl group? b) Give the names of any three alkyl radicals. How are they formed? 12) Define a functional group. Give two examples with structural formula of: a) halides b) alcohols c) aldehydes 13) Identify the functional groups in the following: a) CH3OH, b) HCHO c) CH3COOH. 14) Name the alkyl radical and functional group present in the following: a) CH3OH b) C2H5OH c) C3H7CHO d) C4H9COOH 15) Carbon shows some unique properties. Name them 16) Explain the following: a) tetravalency b) catenation 17) Give at least one example in each case to show structure of isomers of a) single bond compound b) double bond compound c) triple bond compound. 18) Name the following organic compound using IUPAC nomenclature CH3 | H 3C C CH2 CH2 CH3 a) b) CH3 C C CH2 CH3 | CH3 Cl CH3 | | CH CH CH CH2 CH3 3 c) H C C C H d) | | Cl CH 3 e) CH3 CH3 | | CH2 CH CH2 | CH2 CH2 CH3 g) CH3 C C CH3 i) CH3 | CH3 C CH2CH2 CH3 | CH3 f) CH3 | CH3 CH CH2 CH3 h) CH3 CH CH2 CH2 CH3 | OH CH3 | j) CH3 CH2 C CH2CH2 CH3 | CH3 19) Write the structures of the following compounds a) Prop-1 ene b) 2, 3-dimethylbutane c) 2-methylpropane d) 3-hexene e) Prop-1-yne f) 2-methylprop-1-ene 20) Choose the correct answer: a) C5H11 is an i) alkane ii) alkene iii) alkyne iv) alkyl group b) A hydrocarbon having general formula CnH2n is i) C15H30 ii) C12H26 iii) C8H20 iv) C6H14 80 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry 81 c) A hydrocarbon with molecular mass 72 is i) an alkane ii) an alkene iii) an alkyne d) The total number of different carbon chains that four carbon atoms form in alkane is: i) 5 ii) 4 iii) 3 iv) 2 e) CH3 CH2 OH and CH3 O CH3 are i) position isomers ii) chain isomers iii) homologues iv) functional-group isomers f) The IUPAC name of the compound CH3 | CH3 CH2 CH CH2 CH2 CH3 i) 3-trimethylhexane ii) 3-methyl hexane iii) 4-methyl hexane 21) Fill in the blanks using the appropriate words given in the brackets. a) Propane and ethane are _______ (homologues, isomers) b) A saturated hydrocarbon does not participate in a/an _____ reaction (substitution, addition) c) Succeeding members of a homologous series differ by _______ (CH, CH2, CH3) d) As the molecular masses of hydrocarbons increase, their boiling points _______ and melting point _______ (increases, different) e) C25H52 and C50H102 belong to _______ homologous series (the same, different) f) CO is an _______ compound. (organic, inorganic) g) The physical and chemical properties of an organic compound are largely decided by the _______ (functional group, number of carbon atoms) h) CHO is the functional group of an _______ (alcohol, aldehyde) i) The root in the IUPAC name of an organic compound depends upon the number of carbon atoms in _______ (any chain, principal chain) j) But-1-ene and but-2-ene are examples of _______ isomerism. (chain, position functional) Alkanes: 1) What are the main sources of alkanes? Give their general formulae. 2) Write (a) molecular formula (b) electron dot formula (c) structural formula of methane and ethane 3) How is (a) methane, and (b) ethane prepared in the laboratory? 4) How are methane and ethane prepared from methyl iodide and ethyl bromide? 5) What is a substitution reaction? Give the reaction of chlorine with ethane and name the product formed. 6) What happens when methane burns in insufficient air? Give the balanced equation. 7) Write the names and formulae of the products formed when methane reacts with: a) Chlorine b) Bromine Write chemical equations. 8) Give the chemical equations for the combustion of methane and ethane in excess of oxygen. 9) Give three uses of: a) Methane and b) Ethane 10) Under what conditions does ethane get converted to: a) Ethyl alcohol b) Acetaldehyde c) Acetic acid 11) Show giving structural formulae the inter relationship of methane, methyl alcohol, acetaldehyde and formic acid. 12) Give the general formula of alkanes 13) Draw the structures of isomers of a) butane b) pentane Write the IUPAC and common names of these isomers. Volume 2 of 2 Universal Tutorials X ICSE Chemistry 81 82 14) Name the compounds prepared from a) sodium propionate b) methyl iodide c) ethyl bromide Write balanced equations for the same. Alkenes: 1) Write; (a) molecular formulae, (b) electron dot formulae and (c) structural formulae of ethene (ethylene) 2) The molecules of alkene family are represented by a general formula CnH2n. Now answer the following: a) What do n and 2n signify? b) What is the lowest value of alkene when n = 4? c) What is the molecular formula of alkene when n = 4? d) What is the molecular formula of the alkene if there are eight H atoms in it? e) What is the molecular formula of the first member of the alkene family? 3) Give the balanced equation for lab. preparation of ethylene. How is the gas collected? 4) Give the conditions and the main product formed by hydrogenation of ethylene. 5) Ethylene when reacts with halogens (chlorine and bromine) form saturated products. Name them. 6) How is ethanol converted to ethene using a solid as dehydrating agent and not conc. H2SO4? Give only balanced equation. 7) Write the following properties of ethene: a) Physical state b) Odour c) Density as compared to air d) Solubility 8) How would you convert: a) ethene to 1,2-dibromoethane? b) ethene to ethyl bromide? 9) Give the formulae and names of A, B, C and D in the following equations. Cl 2 / HCl Cl 2 / HCl Cl 2 / HCl Cl 2 / HCl a) CH4 A B C D H Br / HBr H Br / HBr 2 2 2 2 A B C D b) C2H2 c) C2H4 + Cl2 A 200 C Ni d) C2H4 + B C2H6 10) Write the name of formula of the product formed in each case below: Sunlight a) CH4 + Cl2 b) C2H5Br + KOH (alc) alk.KMnO4 c) H2C = CH2 d) H2C = CH2 + HBr e) H2C = CH2 + O3 Alkynes: 1) What are the sources for alkynes? Give their general formulae. 2) How is acetylene prepared in the laboratory? a) Draw a figure for the same b) give an equation for the same c) How is the gas collected 3) What are alkynes? Name two members of this group and draw their structures. 4) Why does ethyne show addition reaction? 5) What is the catalytic hydrogenation of ethyne? Explain with equations. 6) What are the products formed when ethyne is added to a) chlorine b) bromine c) iodine d) hydrogen? 7) Give a chemical test to distinguish between saturated and unsaturated compounds. 8) Give a chemical test to distinguish between: a) ethane and ethene b) ethene(ethylene) and ethyne (acetylene) 82 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry 83 9) Write equations to show what happens when acetylene gas (Ethyne gas) reacts with: a) bromine water b) excess of hydrobromic acid 10) Why alkynes are considered as unsaturated compounds. 11) Give the method of preparation of ethyne from 1,2 dibromoethene. 12) Classify the following compounds as alkanes, alkenes and alkynes? C3H4, C3H8, C5H8, C3H6 13) What do you observe when ethyne reacts with chlorine in the presence of sunlight. 14) Name the main organic compounds prepared by ethyne. 15) Give three uses of ethyne. Alcohols: 1) Give the structure of first two members of alcohols 2) Give the manufacturing process of ethanol. 3) How is ethanol prepared by fermentation? 4) Name the products formed and give appropriate chemical equations for the following. a) Sodium reacts with ethyl alcohol b) Ethanol is oxidized by K2Cr2O7 5) Give a lab. preparation of: a) ethyl alcohol. b) methyl alcohol 6) Give the trival names and IUPAC names of the following: a) C2H6 b) C2H4 c) C2H2 d) CH3OH e) C2H5OH 7) Ethanol can be oxidized to ethanoic acid. Write the equation and name the oxidizing agent. 8) How are the following obtained: a) absolute alcohol b) spurious alcohol c) denatured alcohol Carboxylic Acids: 1) What are carboxylic acids? Give their general formula. 2) Write the names of first three members of carboxylic acid series. 3) What is glacial acetic acid? 4) Complete: a) Vinegar is prepared by the bacterial oxidation of ___________ b) The organic acid present in vinegar is ___________ c) The next higher homologue of ethanoic acid is ___________ 5) How is acetic acid prepared from ethanol? 6) How is acetic acid manufactured from acetylene? 7) What do you notice when acetic acid react with a) litmus b) metals c) alkalies d) alcohol 8) Acetic acid is a typical acid. Write one equation in each case for its reaction with a) a metal b) a base/alkali c) a carbonate 9) Name: a) Compound formed when acetic acid and ethanol react together b) Reducing agent used to convert acetic acid to ethanol c) Substance used to change acetic acid to acetic anhydride. 10) Give two test to show CH3COOH is acidic in nature. HOME WORK EXERCISE: 1) Draw the structural formula of a compound with two carbon atoms in each of the following cases. a) An alkane with a carbon to carbon single bond b) An alcohol containing two carbon atoms. c) An unsaturated hydrocarbon with a carbon to carbon triple bond. 2) Ethane, Ethene, Ethanoic acid, Ethyne, Ethanol Volume 2 of 2 Universal Tutorials X ICSE Chemistry 83 84 From the box: name a) The compound with OH as the part of its structure b) The compound with COOH as the part of its structure c) Homologue of homologous series with general formula CnH2n. 3) Give the correct IUPAC name and the functional group for each of the compounds whose structural formulae are given below: H H O H H H a) b) | | || | | | H C C C H H C C C OH | | | | | H H H H H 4) a) Write the equation for the preparation of carbon tetrachloride from methane. b) Draw the structural formula of ethyne. c) How is the structure of alkynes different from that of alkenes? 5) Fill in the blanks with the correct words from the brackets: Alkenes are the (a) _______ (analogous/ homologous) series of (b) _______ (saturated/ unsaturated) hydrocarbons. They differ from alkanes due to the presence of (c) _______ (double/ single) bonds. Alkenes mainly undergo (d) _______ (addition/ substitution) reactions. 6) Give the IUPAC names of the following compounds numbered (i) to (v). The IUPAC names of the compounds on the left are to guide you into giving the correct IUPAC names of the compounds on the right. H H H H | | | | Propene H C C=C H C C C H | | | i) _____________ H H H H H H H H H H H H H | | | | | | | | | | Pentan -2- ol H C C C C C H H C C C C C H | | | | | | | | | | H H H O H H H OH H H H ii) _____________ H | H C H H H H H H | | | | | H C C C H 2,2-dimethylpropane H C C C H | | | | H H H H H C H H C H | | H iii) _____________ H Propanoic acid H O | || H C C | | H OH H H O | | || H C C C | | | H H OH iv) _____________ 84 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry 1,2-dibromoethane 85 H H | | H C C H | | Br Br H H | | H C C H | | Cl Cl v) _____________ 7) Copy and complete the following table which relates to three homologous series of Hydrocarbons: General Formula IUPAC name of the homologous series Characteristic bond type IUPAC name of the first member of the series Type of reaction with chlorine. CnH2n CnH2n 2 CnH2n+2 Single bonds Addition ANSWERS: Class Work: Organic Compounds: 1) Hydrocarbons are compounds that are made up of carbon and hydrogen have molecular formula CxHy, where x and y are whole numbers. Hydrocarbons are subdivided into two main groups, the aliphatic and aromatic cyclic or open chain and closed chain hydrocarbons. The open chain compounds are further divided into saturated compounds i.e. those which have carbon carbon single bond and unsaturated compounds with carbon carbon double or triple bonds. Hydrocarbons Aliphatic or open chain compounds Saturated Alkanes (Paraffins) Cyclic or closed chain compounds Unsaturated Alkenes (Olefins) CnH2n Alicyclic Aromatic Alkynes CnH2n 2 Where n stands for the number of carbon atoms Saturated organic compounds Unsaturated organic compounds All the four valencies of each carbon atom are satisfied by forming single covalent bonds either with carbon or with hydrogen atoms. The valencies of at least two carbon atoms are not fully satisfied by the hydrogen atoms. Carbon atoms are joined only by a single covalent bond > C C <. Carbon atoms are joined by double covalent bonds > C = C < or triple covalent bonds C C Due to the non availability of electrons in the single covalent bond, they are less reactive and therefore undergo characteristic substitution reaction. Eg. CH4 Methane; C2H6 Ethane Due to the availability of electrons in the double covalent bond or triple bond. They are more reactive and therefore undergo characteristic addition reaction. Eg. H H H C=C H C=C [ethyne] H H Acetylene [ethene] Ethylene Volume 2 of 2 Universal Tutorials X ICSE Chemistry 85 86 2) There are a large number of organic compounds because Carbon has a unique nature i) It is tetravalent ii) It shows catenation property iii) It forms single double and triple covalent bonds to satisfy its valency. 4) a) Homologous Series: A homologous series is a group of organic compounds having similar structure & similar chemical properties in which the successive compounds differ by a CH2 group b) i) 14 amu ii) > CH2 5) Compounds represented by the same molecular formulae but different structural formulae are called isomers while the phenomenon is known as isomerism. In case of organic compounds, one molecular formula may represent more than one compound having different properties. For example: C4H10O stands for three different ethers. CH3 O CH(CH3)2 C2H5 O C2H5 CH3 O CH2C2H5 Diethyl ether Methyl n propyl ether Methyl iso propyl ether The isomers have different properties due to the difference in the arrangement of their atoms. There are two main causes of isomerism i) Difference in the mode of linking of atoms: For example: C4H10O shows different types of linkages and thus it stands for three different types of ether. C2H5 O C2H5 CH3 O C3H7 CH3 O CH(CH3)2 Diethyl ether Methyl propyl ether Methyl iso propyl ether This type of isomerism is structural isomerism. ii) Difference in the arrangement of atoms or groups in space For example: 1,2-dichloro ethane H H H C=C Cl Cl C=C Cl Cl H This type of isomerism is stereo isomerism. 6) a) C6H14 = hexane b) CH3 CH CH CH3 | | 2, 3 dimethylbutane CH3 CH3 7) Organic compounds Inorganic compounds Carbon is a necessary element in every Carbon is not an essential element in every organic compound. inorganic compound. They generally do not dissolve in water. They generally dissolve in water. They dissolve in organic solvents like They do not dissolve in organic solvents. alcohol, benzene and chloroform. They have low m.p. and decompose on They have high m.p. and usually do not heating. decompose on heating. 8) a) Saturated hydrocarbon: Alkane, Methane, b) Unsaturated hydrocarbon: Alkene, Ethene 9) Name Molecular formulae Structural formula Condensed formula H | CH4 Methane CH4 H C H | H 86 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry Name Ethane Propane 10) a) 87 Molecular formulae C2H6 Structural formula H H | | H C C H | | H H Condensed formula CH3CH3 H H H | | | H C C C H | | | H H H C3H8 CH3 | CH3 C CH3 | CH3 b) CH3 CH CH2 CH3 | CH3 CH3 CH2 CH3 c) H H H | | | H C=C C H | H a) 2, 2 dimethyl propane b) 2 methyl butane c) 1, 2 prop 1 ene 11) a) An alkyl group or alkyl radical is obtained by removing one atom of hydrogen from alkane molecule. General formula: >CnH2n+1 An alkyl group is named by changing the suffix ane of the alkane with suffix yl . The alkyl group has unpaired electron which is indicated by a line. b) Methyl CH3 ethyl C2H5; propyl C3H7, they are formed by removing, 1H atom from the parent alkane. 12) Functional Group: It is an atom or a group of atoms which defines the structure (or properties of a particular family) of organic compounds such as Halides F, Cl, Br; aldehydes CHO; alcohols OH, and carboxylic acids COOH. b) CH3OH, C2H5OH c) HCHO, C2H5CHO a) CH3I, C2H5Br 13) a) OH (alcohol) b) CHO (aldehyde) c) COOH (carboxylic acid) 14) a) CH3 OH methyl alcohol b) C2H5 OH ethyl alcohol d) C4H9 CHO butyl aldehyde c) C3H7 CHO Propyl aldehyde 15) Tetravalency, Catenation, Isomerism 16) a) Tetravalency: The characteristic of the carbon atom, by virture of which it forms four covalent bonds, is called the tetravalency of carbon. b) Catenation: The propertyof self-linking of carbon atoms through covalent bonds in order to form straight or branched chains and rings of different sizes is known as catenation. CH3 | 17) a) CH3 C CH3 | CH3 neo-pentane (2,2-dimethyl propane) b) CH3CH = CH CH3 and but-2-ene c) CH3 CH2C C H and but-1-yne 18) a) 2,2, dimethyl pentane Volume 2 of 2 CH2 = CH CH2 CH3 1 butene CH3 C C CH3 but- 2-yne b) 2-Pentyne Universal Tutorials X ICSE Chemistry 87 88 c) 3-methyl 1 butyne d) 2,3-dichloro pentane e) 3-methylhep ptane g) but 2 yne e i) 2,2-dimethyl pentane 2 19) a) CH2 = CH CH3 c) CH3 CH CH3 | CH3 e) C C CH3 f) 2-methyl 2 buta ane h) 2-Hydroxy 2 pentane hexane j) 3,3 dimethyl 3 b) CH3 CH CH CH3 | | CH3 CH C 3 d) CH3 CH2 CH = CH CH2 CH3 C 2 = C CH H3 f) CH | CH3 b) C15H30 c) an a alkane e) functional-gr roup isomers s b) addition c) CH C 2 f) inorganic g) functional f gr roup j) position p kyl group 20) alk f) 3 d) 2 3 methyl hex xane 21) a) homologues d) increase e) same h) a aldehyde i) principal p cha ain Alkanes: 1) Th he principal sources of alkanes a are natural gas and petrole eum. Natural l gas contain ns mainly me ethane with smaller s amounts of ethan ne, propane and butane. Ge eneral Formu ula CnH2n+2 C2H6 2) Mo olecular form mula: CH4 H H Ele ectronic dot H C H C H H C H H H | Structural form mula H C H | H H H H H | | H C C H | | H H 3) a) Laboratory y preparation n of methan ne He eating a mixture of sodium etha anoate (sodi ium ac cetate) and soda lime. Soda lime is i a mixture e of so odium hydrox xide and calcium oxide. It is in form m of wh hite porous mass m or gran nules. Pr rocedure: A mixture of sodium etha anoate (sodi ium ac cetate) and soda s lime is taken in the hard glass test t tub be (as show wn in Fig.) and a heated with a Buns sen fla ame. CaO O 300 C Na2CO3 + CH4 Re eaction: CH3COONa + NaOH N 88 U Universal Tuto orials X ICS SE Chemistr ry Volu ume 2 of 2 Chapter 12: Organic Chemistry 89 Collection: The gas evolved is collected by the downward displacement of water as it is slightly soluble in water and lighter than air. b) Laboratory preparation of ethane: By heating a mixture of sodium propanoate (sodium propionate) and soda lime. Procedure: A mixture of sodium propanoate and soda lime is taken in the boiling tube and heated with a Bunsen flame. CaO 300 C Reaction: C2H5COONa + NaOH Na2CO3 + C2H6 Collection: The gas is evolved which is collected by the downward displacement of water. 4) By the reduction of iodomethane (methyl iodide) and (ethyl bromide) at ordinary temperature by nascent hydrogen. CH3I + 2[H] CH4 + HI C2H5Br + H2 C2H6 + HBr 5) Substitution reaction: The product formed by substituting the hydrogen atom in on alkane, this type of reaction as known. Methane reacts with chlorine in diffused sunlight or when heated to 600K to give chloromethane. diffused sunglight CH3Cl + HCl CH4 + Cl2 or 600K H H | | H C H + Cl2 H C Cl + H Cl | | H H In this reaction, CH3Cl is formed by the substitution of a hydrogen atom in the methane molecule by a chlorine atom. This type of reaction is known as substitution reaction and the product formed is known as substitution product. 6) 2CH4 + 3O2 2CO + 4H2O (insufficient supply of air) CH4 + O2 C + 2H2O (with still less O2) diffused sunlight or 600K 7) CH4 + Cl2 CH3Cl (chloromethane) + HCl diffused sunlight or 600K CH4 + Br2 CH3Br (bromomethane) + HBr 2C2H6 + 7O2 4CO2 + 6H2O (excess of O2) 8) CH4 + 2O2 CO2 + 2H2O (excess of O2) 9) a) Methane (i) Methane is a source of carbon monoxide and hydrogen. (ii) It is used in the preparation of ethyne (acetylene), methanal (formaldehyde), methanol, chloromethane and tetrachloro methane (carbon tetrachloride). (iii) It is employed as a domestic fuel. b) Ethane (i) Ethane is used in the preparation of ethene, ethanol, ethanal, (acetaldehyde) and ethanoic acid (acetic acid) (ii) It forms ethyl chloride, which is used to make tetraethyl lead. (iii) It is also a good fuel. 120 atm Cu tubes 475K 10) 2C2H6 + O2 2C2H5OH MoO CH3CHO + H2O C2H6 + O2 120 atm Cu tubes 475K 2C2H5OH + 2[O] CH3COOH + H2O 2C2H6 + O2 11) H | H C H | H Methane Volume 2 of 2 (O) H | (O) H C OH | H methyl alcohol H | C=O | H H | (O) C OH || O formic acid (O) Universal Tutorials X ICSE Chemistry CO 2 + H2O 89 90 12) CnH2n+2 13) a) Isomers of butane (C4H10): Butane has four carbon atoms. These four carbon atoms can be arranged in two distinct ways. Therefore, there are two isomers of butane. H H H H H H H | | | | | | | H C C C H H C C C C H | | | | | | H H H H H H H C H | H Iso-butane (C4H10) IUPAC Name : 2 Methyl propane n butane (C4H10), where n stands for normal IUPAC Name: Butane b) Isomers of pentane (C5H12): Pentane has five carbon atoms, which can be arranged in three different ways. Therefore pentane can form three isomers. H H H H H H | | | | | | H C C C C C C H | | | | | | H H H H H H Common Name: n-pentane IUPAC Name: Pentane [ n , means no carbon atom is attached to more than two carbon atoms] CH3 | CH3 CH CH2 CH3 Common name : isopentane IUPAC Name : 2-methyl butane [ iso , i.e. at least one carbon atom is attached to three other carbon atoms] CH3 | CH3 C CH3 | CH3 Common name : neo-pentane IUPAC Name : 2, 2 dimethyl propane [ neo , i.e. at least one carbon atom is attached to four other carbon atoms]. CaO,300 C 14) a) ethane, C2H5COONa + NaOH Na2CO3 + C2H6 b) methane, CH3I + 2[H] CH4 + HI c) ethane, C2H5Br + 2[H] C2H6 + HBr Alkenes: 1) a) C2H4 b) H H C H C H c) H H | | H C=C H 2) a) n and 2n signify whole nos. applicable to carbon atoms present in the molecule. b) C4H8 c) C4H8 d) C4H8 e) C2H4 90 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: 1 Organic Chemistry C 91 3) Re eaction: CH3CH2OH +H2SO S 4 CH3 CH C 2HSO4 + H2O excess H SO O 4 CH H3CH2HSO4 2 CH2= CH2 + H2SO4 160 C Co ollection: The T gas is collected by b the dow wnward dis splacement of o water bec cause (i) it is s inflammabl le gas. (ii) ) it is insoluble in water. 4) Ad ddition of hyd drogen (Hydrogenation): When ethan ne and hy ydrogen are passed p over r finely divide ed catalyst such as pla atinum or palladium at or rdinary temperature or nickel at 20 00 C, the two o atoms of hy ydrogen molecule are ad dded to un nsaturated molecule whic ch thus chang ges to a satu urated one. 200 C Ni C2H6 C2H4 + H2 5) 1,2 2 Dichloro et thane; 1,2-dibromo ethan ne Al O 300 C 2 3 C2H4 + H2O 6) C2H5OH 7) a) colourless in nflammable gas g c) lighter than air 8) CH2 = CH2 + Br B 2 CH2 CH2 | | Br Br sh smell b) Faint sweetis w d) Insoluble in water CH H2 = CH2 + HBr CH3 CH2Br ethyl bromide e Cl / HCl Cl 2 / HCl Cl 2 / HCl 2 CHCl3 9) a) CH4 C 4 CH2Cl2 CCl H H Br / HBr Br r / HBr 2 2 2 2 C2H4 C2H6 C2H5Br C2H4Br2 b) C2H2 br rome ethene dibr romo ethene c) C2H4 + Cl2 C2H4Cl2 200 C Ni d) C2H4 + H2 C2H6 Sunlight 10) a) CH4 + Cl2 C 4 CCl c) H2C = CH2 + H2O + [O] CH2 CH H2 | | OH OH H e) H2C = CH2 + O3 H2C O CH2 | | O O b) C2H5Br + KO OH(alc) C2H4 + KBr + H2O d) H2C = CH2 + HBr CH3 CH2 Br Et thane ozonide Alkynes: 1) Traces of alkynes are pres sent in coal gas g and in gases g obtained by the de ecomposition n of some co omplex organ nic compoun nds. It is obta ained by the crackling of f alkanes from m various fra actions of pe etroleum. Ge eneral formula, CnH2n 2 2) It is i prepared by b the action n of water on calcium carb bide. Pr rocedure: Arr range the ap pparatus as shown s in Fig. . Ta ake few piec ces of calciu um carbide in a conical flask. Add few dro ops of water through th he thistle fun nnel. Calcium m carbide re eacts wit th water to produce p acety ylene gas. It is an exothe ermic reactio on. Re eaction: CaC C2 + 2H2O Ca(OH)2 + C2H2 Co ollection: Th he gas is col llected by the e downward displacement of water b because it is insoluble in water. 3) alk kynes are un nsaturated hy ydrocarbons having triple e bonds ( ) present p between two carb bon atom. Eg g. C C Volume 2 of 2 U Universal Tuto orials X ICS SE Chemistr ry 91 92 Molecular formula Condensed formula Structural formula Trivial name IUPAC name of the compound C2H2 CH CH H C C H Acetylene Ethyne H | C3H4 Propyne CH3 C CH H C C C H | H 4) Ethyne shows addition reaction because of the presence of triple bonds between two carbon atoms. 5) Addition of hydrogen (Catalytic hydrogenation): In the presence of nickel, platinum or palladium ethyne first adds two atoms of hydrogen to change to ethane, which further adds two atoms of hydrogen to give ethane. Ni First stage of reaction: C2H2 + H2 C2H4 Ni Second stage: C2H4 + H2 C2H6 +H / Ni +H / Ni Therefore, HC CH 2 CH2 = CH2 2 CH3 CH3 + Cl + Cl +Br 2 2 C2H2Cl2 C2H2Cl4 6) a) C2H2 +I +Br 2 2 b) C2H2 C2H2Br2 C2H2Br4 +I 2 2 C2H2I2 C2H2I4 c) C2H2 Ni Ni C2H4; C2H4 + H2 C2H6 d) C2H2 + H2 7) Saturated organic compounds undergo substitution reaction, CH4 + Cl2 CH3Cl + HCl Unsaturated organic compounds undergo addition reaction, Ni Ni C2H4 + H2 C2H6 C2H2 + H2 C2H4; C2H4 + H2 C2H6 8) a) ethane will undergo substitution reaction, C2H6 + Cl2 C2H5Cl + HCl Ethene will undergo addition reaction, CH2 = CH2 + Cl2 CH2 CH2 | | Cl Cl b) Ethylene and acetylene both undergo addition reaction Ni C2H2 + H2 C2H4; +Br2 Ni C2H4 + H2 C2H6 +Br2 +HBr +HBr CH2CHBr CH3CHBr2 9) a) C2H2 C2H2Br2 C2H2Br4 b) C2H2 10) The aliphatic hydrocarbons that contain a triple bond ( C C ), i.e. an acetylenic bond, between two carbon atoms are known as alkynes. They are unsaturated compounds, due to the triple bond between two carbon atoms, they form a homologous series. 11) When 1, 2 dibromoethane (ethylene dibromide) is boiled with alcoholic potassium hydroxide, ethyne is formed. alcohol CH + 2KBr + 2H2O CH2Br + 2KOH boil CH2Br (alcoholic) CH (Ethyne) 12) alkyne (C3H4), alkane (C3H8), alkyne (C5H8), alkene (C3H8). 13) Reaction with chlorine: + Cl2 + Cl2 C2H2 C2H2Cl2 C2H2Cl4 Ethyne Acetylene (Acetylene) dibromide 1,2dichloroethane Acetylene tetrabromide 1,1,2,2 tetrachloro ethane Acetylene reacts explosively with chlorine gas in the presence of sunlight bursting into flames. C2H2 + Cl2 2C + 2HCl 92 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry 93 14) Ethyne is used for the manufacture of synthetic products like polymers, artificial rubber, oxalic acid, etc. for the manufacture of important organic compounds like acetaldehyde, acetic acid, plastic, rubber etc. 15) For oxy-acetylene welding involving very high temperatures, these temperatures are obtained when ethyne burns in oxygen. As an illuminant ripening and preservation of fruits. For artificial ripening and preservation of fruits. Alcohols: H | 1) CH3OH H C OH (methyl alcohol) | H H H | | C2H5OH H C C O H (ethyl alcohol) | | H H 2) When concentrated sulphuric acid is added to ethane at the temperature of 80 C under 30 atmpressure, ethyl hydrogen sulphate is produced. Ethyl hydrogen sulphate on hydrolysis with boiling water gives ethanol. 80 C C2H4 + H2SO4 C2H5HSO4 30 atm C2H5HSO4 + H2O C2H5OH + H2SO4 3) Ethanol is also prepared by fermentation of sugar (molasses) by the enzymes (invertase and zymase) Invertase C12H22O11 + H2O C6H12O6 + C6H12O6 Zymase( Yeast ) C6H12O6 2C2H5OH + 2CO2 Fermentati on 4) a) 2C2H5OH + 2Na 2C2H5ONa + H2 ( O ) K Cr O 7 b) C2H5OH 2 2 CH3CHO 5) a) When concentrated sulphuric acid is added to ethane at the temperature of 80 C under 30 atmpressure, ethyl hydrogen sulphate is produced. Ethyl hydrogen sulphate on hydrolysis with boiling water gives ethanol. 80 C C2H4 + H2SO4 C2H5HSO4 30 atm C2H5HSO4 + H2O C2H5OH + H2SO4 boil b) CH3Br + KOH CH3OH + KBr 6) C2H6 C2H4 C2H2 CH3OH C2H5OH Trival Name Ethane Ethylene Acetylene Methyl alcohol Ethyl alcohol IUPAC Name Ethane Ethene Ethyne Methanol ethanol (O) (O) 7) C2H5OH CH3CHO + H2O CH3COOH. Oxidising agent is nascent (O). C2H4 + Cl2 CH2 + CH2 | | Cl Cl Carboxylic Acids: 1) An organic compound containing the carboxyl group (COOH) is known as carboxylic acid and they possess acidic properties. i.e. O C OH Volume 2 of 2 Universal Tutorials X ICSE Chemistry 93 94 2) a) Formula Common name IUPAC name O || H C OH Formic acid Methanoic acid Acetic acid Ethanoic acid CH3 O || C OH O Propionic acid Propanoic acid || CH3 CH2 C OH 3) The anhydrous acid on cooling forms crystalline mass resembling ice; melting point 17 C and for this reason it is called glacial acetic acid. O || 4) a) C2H5OH b) CH3COOH c) CH3 CH2 C OH 5) From ethanol: Acetic acid can also be prepared by passing alcohol vapours over platinum black as catalyst at 300 C in presence of oxygen. o 300 C2H5OH + O2 CH3COOH + H2O 6) H2SO4 at 60 C in the presence of 1% HgSO4 (catalyst). H SO ( dil.) 2 4 CH3COOH C2H2 + H2O HgSO4 The acetaldehyde is oxidized to acetic acid by passing a mixture of acetaldehyde vapours and air over manganous acetate at 70 C. 2CH3CHO + O2 2CH3COOH 7) a) Litmus turns red b) 2CH3 COOH + 2Na 2CH3 COONa + H2 c) 2CH3 COOH + Na2CO3 2CH3COONa + H2O + CO2 d) Formation of ester (Esterification). Acetic acid reacts reversibly with alcohols in presence of conc. H2SO4 forming esters. H2SO 4 CH3CO OH + H OC2H5 CH3COOC2H5 + H2O 8) a) 2CH3 COOH + 2Na 2CH3 COONa + H2 b) CH3COOH + NaOH CH3COONa + H2O c) 2CH3 COOH + Na2CO3 2CH3COONa + H2O + CO2 9) a) CH3COOC2H5 b) Pt black c) Acetylene 10) a) CH3COOH + NaOH CH3COONa + H2O b) 2CH3 COOH + 2Na 2CH3 COONa + H2 Home Work Answers: H H | | 1) a) H C C H | | H H 2) a) ethanol 3) a) propanoic acid 94 H H | | b) H C C OH | | H H b) ethanoic acid b) propyl alcohol c) H C C H c) ethene Universal Tutorials X ICSE Chemistry Volume 2 of 2 Chapter 12: Organic Chemistry 95 diffused sunlight 4) a) CH4 + Cl2 CH3Cl + HCl or 600K CH3Cl + Cl2 CH2Cl2 + HCl Chloromethane Dichloromethane CH2Cl2 + Cl2 CHCl3 + HCl Dichloromethane Trichloromethane (Chloroform) CHCl3 + Cl2 CCl4 + HCl Trichloromethane Tetrachloromethane (Carbon tetrachloride) b) H C C H c) presence of in alkynes and presence of = in alkenes 5) a) homologous b) unsaturated c) double d) addition 6) i) propyne, ii) 3 pentanol, iii) 2 methyl propane, iv) ethanoic acid, v) 1, 2, dichloro ethane 7) Copy and complete the following table which relates to three homologous series of Hydrocarbons: General Formula IUPAC name of the homologous series Characteristic bond type IUPAC name of the first member of the series Type of reaction with chlorine. Volume 2 of 2 CnH2n alkene double bond ethene Addition Universal Tutorials X ICSE Chemistry CnH2n 2 alkyne triple ethyne Addition CnH2n+2 alkane Single bonds methane substitution 95 96 Board Paper: Chemistry 2014 SCIENCE Paper 2 (Two hours) Answers to this Paper must be written on the paper provided separately. You will not be allowed to write during the first 15 minutes. This time is to be spent in reading the Question Paper. The time given at the head of this paper is the time allowed for writing the answers. Section I is compulsory. Attempt any four questions from Section II The intended marks for questions or parts of questions are given in brackets [ ]. Section I (40 Marks) Attempt all questions from this Section Question 1 a) Choose the correct answer from the options given below: i) Ionisation Potential increases over a period from left to right because the: A) Atomic radius increases and nuclear charge increases B) Atomic radius decreases and nuclear charge decreases C) Atomic radius increases and nuclear charge decreases D) Atomic radius decreases and nuclear charge increases. ii) A compound X consists of only molecules. Hence X will have: A) A crystalline hard structure B) A low melting point and low boiling point C) An ionic bond D) A strong force of attraction between its molecules. iii) When fused lead bromide is electrolysed we observe: A) a silver grey deposit at anode and a reddish brown deposit at cathode B) a silver grey deposit at cathode and a reddish brown deposit at anode C) a silver grey deposit at cathode and reddish brown fumes at anode D) silver grey fumes at anode and reddish brown fumes at cathode. iv) The main ore used for the extraction of iron is: A) Haematite B) Calamine C) Bauxite D) Cryolite v) Heating an ore in a limited supply of air or in the absence of air at a temperature just below its melting point is known as: A) smelting B) ore dressing C) calcinations D) bessemerisation vi) If an element A belongs to Period 3 and Group II then it will have, A) 3 shells and 2 valence electrons B) 2 shells and 3 valence electrons C) 3 shells and 3 valence electrons D) 2 shells and 2 valence electrons vii) The molecule containing a triple co-valent bond is: A) ammonia B) methane C) water D) nitrogen viii) The electrolyte used for electroplating an article with silver is: A) silver nitrate solution B) silver cyanide solution C) sodium argentocyanide solution D) nickel sulphate solution ix) Aluminium powder is used in thermite welding because, A) it is a strong reducing agent B) it is a strong oxidising agent C) it is corrosion resistant D) it is a good conductor of heat. x) The I.U.P.A.C. name of acetylene is, A) propane B) propyne C) ethane D) ethyne. [10] 96 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Board Paper 2014 97 b) Fill in the blanks from the choices given within brackets: i) The basicity of Acetic Acid is _________ (3, 1, 4) ii) The compound formed when ethanol reacts with sodium is _________ (sodium ethanoate, sodium ethoxide, sodium propanoate) iii) Quicklime is not used to dry HCl gas because _________ (CaO is alkaline, CaO is acidic, CaO is neutral) iv) Ammonia gas is collected by _________ (an upward displacement of air, a downward displacement of water, a downward displacement of air) v) Cold, dilute nitric acid reacts with copper to form _________ (Hydrogen, nitrogen dioxide, nitric oxide). [5] c) Give one word or phrase for the following: i) The ratio of the mass of a certain volume of gas to the mass of an equal volume of hydrogen under the same conditions of temperature and pressure. ii) Formation of ions from molecules. iii) Electrolytic deposition of a superior metal on a baser metal. O || iv) Hydrocarbons containing a C functional group. v) The amount of energy released when an atom in the gaseous state accepts an electron to form an anion. [5] d) Match the options A to E with the statements (i) to (v): A) alkynes i) No. of molecules in 22.4 dm3 of carbon dioxide at s.t.p B) alkane ii) An element with electronic configuration 2, 8, 8, 3 C) iron iii) CnH2n+2 23 iv) CnH2n 2 D) 6.023 10 E) metal v) The metal that forms two types of ions [5] e) Write balanced equations for the following: i) Action of heat on a mixture of copper and concentrated nitric acid. ii) Action of warm water on magnesium nitride. iii) Action of concentrated sulphuric acid on carbon. iv) Action of dilute hydrochloric acid on sodium sulphide. v) Preparation of ethane from sodium propionate. [5] f) Distinguish between the following pairs of compounds using the test given within brackets: i) Iron(lI) sulphate and iron(III) sulphate (using ammonium hydroxide) ii) A lead salt and a zinc salt (using excess ammonium hydroxide) iii) Sodium nitrate and sodium sulphite (using dilute sulphuric acid) iv) Dilute sulphuric acid and dilute hydrochloric acid (using barium chloride solution) v) Ethane and ethene (using alkaline potassium permanganate solution) [5] g) i) Oxygen oxidises ethyne to carbon dioxide and water as shown by the equation: 2C2H2 + 5O2 4CO2 + 2H2O What volume of ethyne gas at s.t.p. is required to produce 8.4 dm3 of carbon dioxide at s.t.p.? [H = 1, C = 12, O = 16] ii) A compound made up of two elements X and Y has an empirical formula X2Y. If the atomic weight of X is 10 and that of Y. is 5 and the compound has a vapour density 25, find its molecular formula. [5] Volume 2 of 2 Universal Tutorials X ICSE Chemistry 97 98 Section II (40 Marks) Attempt any four questions from this Section Question 2 a) State your observation in each of the following cases: i) When dilute hydrochloric acid is added to sodium carbonate crystals. ii) When excess sodium hydroxide is added to calcium nitrate solution. iii) At the cathode when acidified aqueous copper sulphate solution is electrolyzed with copper electrodes. iv) When calcium hydroxide is heated with ammonium chloride crystals. v) When moist starch iodide paper is introduced into chlorine gas. [5] b) Study the figure given below and answer the questions that follow: i) Identify the gas Y. ii) What property of gas Y does this experiment demonstrate? iii) Name another gas which has the same property and can be demonstrated through this experiment. [3] c) i) Name the other ion formed when ammonia dissolves in water. ii) Give one test that can be used to detect the presence of the ion produced. Question 3 a) State the conditions required for the following reactions to take place: i) Catalytic hydrogenation of ethyne. ii) Preparation of ethyne from ethylene dibrornide. iii) Catalytic oxidation of ammonia to nitric oxide. iv) Any two conditions for the conversion of sulphur dioxide to sulphur trioxide. b) State the main components of the following alloys: i) Brass. ii) Duralumin. iii) Bronze. c) Give balanced equations for the following: i) Laboratory preparation of nitric acid. ii) Preparation of ethanol from monochloroethane and aq. sodium hydroxide. [2] [5] [3] [2] Question 4 a) Give the structural formula of the following: [4] i) ethanol. ii) 1-propanal iii) ethanoic acid iv) 1, 2, dichloroethane b) Draw the structure of the stable positive ion formed when an acid dissolves in water. [2] c) State the inference drawn from the following observations: i) On carrying out the flame test with a salt P a brick red flame was obtained. What is the cation in P? ii) A gas Q turns moist lead acetate paper silvery black. Identify the gas Q. iii) pH of liquid R is 10. What kind of substance is R? iv) Salt S is prepared by reacting dilute sulphuric acid with copper oxide. Identify S. [4] 98 Universal Tutorials X ICSE Chemistry Volume 2 of 2 Board Paper 2014 99 Question 5 a) Name the following: i) The property possessed by metals by which they can be beaten into sheets. ii) A compound added to lower the fusion temperature of electrolytic bath in the extraction of aluminium. iii) The ore of zinc containing its sulphide. [3] b) Give one equation each to show the following properties of sulphuric acid: i) Dehydrating property. ii) Acidic nature. iii) As a non-volatile acid. [3] c) Give balanced chemical equations to prepare the following salts: i) Lead sulphate from lead carbonate. ii) Sodium sulphate using dilute sulphuric acid. iii) Copper chloride using copper carbonate. [4] Question 6 a) i) State Avogadro s Law. ii) A cylinder contains 68g of ammonia gas at s.t.p. 1) What is the volume occupied by this gas? 2) How many moles of ammonia are present in the cylinder? 3) How many molecules of ammonia are present in the cylinder? [N-14, H-1] b) i) Why do covalent compounds exist as gases, liquids or soft solids? ii) Which electrode: anode or cathode is the oxidising electrode? Why? c) Name the kind of particles present in: i) Sodium Hydroxide solution. ii) Carbonic acid. iii) Sugar solution. [4] [3] [3] Question 7 a) An element Z has atomic number 16. Answer the following questions on Z: i) State the period and group to which Z belongs. ii) Is Z a metal or a non-metal? iii) State the formula between Z and Hydrogen. iv) What kind of a compound is this? [5] b) M is a metal above hydrogen in the activity series and its oxide has the formula M2O. This oxide when dissolved in water forms the corresponding hydroxide which is a good conductor of electricity. In the above context answer the following: i) What kind of combination exists between M and O? ii) How many electrons are there in the outermost shell of M? iii) Name the group to which M belongs. iv) State the reaction taking place at the cathode. v) Name the product at the anode. [5] Volume 2 of 2 Universal Tutorials X ICSE Chemistry 99
|
