Trending ▼   ResFinder  

ICSE Class IX Board Exam 2025 : Chemistry

30 pages, 0 questions, 0 questions with responses, 0 total responses,    0    0
Sheetal Sharma
Guru Nanak Public School, Chandigarh(Ut)
+Fave Message
ProfileTimelineUploads
 Home > seetalsharmavermamallick >

Formatting page ...

THE CAREER NR Classes ACIDS, BASES AND SALTS ACIDS: The chemical substance which when dissolves in water furnishes H +(aq) or H3O+ ion as the only positively charged ion is called acid. ( ) + ( ) ( ) + ( ) ( ) + ( ) ( ) + ( ) NaHCO3 is not an acid though it gives H+(aq) ion in its aqueous solution because NaHCO3 on dissociation gives Na+(aq) ion and H+(aq) ion as the positively charged ions, and according to the definition of acid, H+(aq) ion should be the only positively charged ion, which doesn t see in this case. ( ) + ( ) + ( ) CLASSIFICATION OF ACIDS Acids are classified according to 1. Source: According to source, acids are classified into two types Mineral/inorganic acids Acids which are obtained from minerals are called mineral acids. Eg:HCl, HNO3, H2SO4, H2CO3,etc. Organic acids Acids which are obtained from organic or living source are called organic acids. Eg:CH3COOH (from vinegar), HCOOH (from sting of red ant and bee), citric acid (from citrous fruit), malic acid(from apples), tartaric acid (from tamarind and grapes), oxalic acid (from tomatoes), etc. 2. Composition: According to composition, acids are classified into two types Hydra acids Acid which contain hydrogen along with some other non-metal but other than oxygen is called Hydra acids. Eg-HCl, HBr, HI, HF, etc. Oxy-acids Acid which contain hydrogen, oxygen along with some other non-metal is called Oxy-acids. Eg:HNO3,H2SO4,H2CO3,CH3COOH, etc. 1|Page Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes 3. Strength: Strength of acid depends upon the amount of H+(aq) or H3O+ ion present in the aqueous solution of an acid. More the number of H+(aq) or H3O+ ion in the aqueous solution of an acid more will be its strength. On dilution strength of an acid increases. According to strength, acids are classified into two types Strong acid Weak acid The acid in which amount of The acid in which amount of H3O+ ion is more in its aqueous H3O+ ion is less in its aqueous solution is called strong acid. solution is called weak acid. All mineral acids are strong All organic acids are weak acids acids 4. Concentration: It depends upon the amount of acid present in its aqueous solution. More the amount of acid relative to water more will be its concentration. On dilution concentration of an acid decreases. According to concentration, acids are classified into two types Concentrated acid Dilute acid The aqueous solution of an acid The aqueous solution of an acid which contain less amount of which contain more amount of water then acid is called water then acid is called dilute concentrated acid. acid. Out of dil. H2SO4 and conc. H2SO4; dil. H2SO4 is a stronger acid as on dilution number of H3O+ ion in the aqueous solution increases and thus the strength increases and the acid becomes stronger. Similarly, dil.CH3COOH is a stronger acid than conc. H 2SO4. Difference between conc. of an acid and strength of an acid Concentration of an acid Strength of an acid It depends upon the amount of Strength of acid depends upon acid present in its aqueous the amount of H+(aq) or H3O+ solution ion present in the aqueous solution of an acid. It decreases with dilution. It increases with dilution 2|Page Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes MI*: Water is never poured on acid to dilute it as large amount of heat is evolved which changes poured water into steam. The steam so formed causes spurting of acid which cause burn injuries, so dilution is done by pouring acid on a given amount of water in controlled manner by continuous stirring, else acid being heavier will settle down. The evolved heat dissipated in the water itself and hence spurting of acid is minimised. 5. Basicity: Basicity of an acid is defined as the number of H+(aq) or H3O+ ion produce per molecule of an acid when dissolved in water. According to basicity, acids are classified into three types: Type of acid Definition with examples Monobasic acid Acids Dibasic acid which gives one H+(aq) or H3O+ ion per molecule of an acid when dissolved in water are called monobasic acids. ( ) + ( ) + ( ) + ( ) + Eg-HCl, HBr, HI, HF, HNO2,HNO3,CH3COOH,etc ( ) + Acids + ( ) + which gives two H+(aq) or H3O+ ion per molecule of an acid when dissolved in water are called dibasic acids. H2SO4, H2CO3, H3PO3 Eg- Tribasic acid Dissociation rection in water H2SO3, Acids which gives three + ( ) + + ( ) + + ( ) + + ( ) + H+(aq) or H3O+ ion per molecule of an acid when dissolved in water are called tribasic acids. Eg- H3PO4, Citric acid 3|Page Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes MI*: It must be emphasized that the basicity of an acid depends upon the number of ionizable hydrogen atom furnished by per molecule of acid when dissolved in water, but not on the number of hydrogen atoms present in one molecule of an acid. SOME IMPORTANT CASES ON BASICITY OF AN ACID: 1. BORIC ACID (H3BO3) Boric acid is a weak monobasic acid because it does not dissociate to give H+(aq) ions of its own rather it form borate ion by accepting OH - ion from water to complete its octet and releases one H+(aq) ions from water. 2. PHOSPHORUS ACID (H3PO3) H3PO3 is a dibasic acid and not tribasic acid because in oxyacids of phosphorus, hydrogen atoms which are attached to oxygen atom are replaceable. Hydrogen atoms directly bonded to phosphorus atom are not replaceable. PREPARATION OF ACIDS 1. By synthesis: This method is generally used to prepare binary acids. H2 + Cl2 2HCl H2 + Br2 2HBr H2 + S H2S 2. By the oxidation of non-metals: A non-metal like S or P is oxidised by conc. Nitric acid to form Sulphuric acid and phosphoric acid respectively. S + 6HNO3 H2SO4 + 2H2O + 6NO2 P + 5HNO3 H3PO4 + H2O + 5NO2 3. By displacement: Normal salts of more volatile acids are displaced by less or non-volatile acid like conc. H2SO4. NaCl + H2SO4 NaHSO4 + HCl NaNO3 + H2SO4 NaHSO4 + HNO3 4|Page Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes 4. By the action of water on non-metallic or acidic oxides: Acidic oxides dissolve in water to give acids. Only oxyacids can be prepared by this method. SO3 + H2O H2SO4 SO2 + H2O H2SO3 CO2 + H2O H2CO3 P2O5 + 3H2O 2H3PO4 P2O5 + 3H2O 2H3PO4 N2O5 + H2O 2HNO3 CO, N2O, NO are the neutral oxides and hence they do not form acid when dissolved in water. NO2 is called double or mixed anhydride because when NO2 reacts with water, forms two different acids i.e. HNO3 (Nitric acid) and HNO2 (Nitrous acid). + + The acidic oxide are called acid anhydride of their corresponding acids. PHYSICAL PROPERTIES OF ACIDS 1. Taste: All acids are sour in taste. Acids like H2SO4 and HNO3 are highly corrosive in nature. Therefore, they should not be tasted. Carbonic acid is a weak non-corrosive acid and so, used in soft drinks. 2. Physical state: ACIDS FORMULA PHYSICAL STATE Boric acid H3BO3 Oxalic acid (COOH)2 Tartaric acid C4H6O6 Solid Citric acid C6H8O7 Phosphoric acid H3PO4 Acetic acid CH3COOH Liquid Formic acid HCOOH (Volatile acids vaporises easily at Carbonic acid H2CO3 room temperature or on heating Hydrochloric acid HCl at about 1000C) Nitric acid HNO3 Sulphurous acid H2SO3 Sulphuric acid H2SO4 Liquid (Non-volatile acid) 3. Effect on skin: All mineral acids have corrosive action on the skin (except H2CO3) and causes painful burns. Conc.H2SO4 stains the skin black Conc.HNO3 stains the skin yellow Conc.HCl gives amber colour to the skin 5|Page Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes 4. Effect on indicators: Indicators are the complex substances that acquire separate colours in acidic and basic mediums. Indicator Colour change in acidic medium Litmus Blue to red Methyl orange Orange to pink Phenolphthalein Remains colourless Alkaline Phenolphthalein Pink to colourless The red cabbage extract (natural indicator) remains red in acidic medium but turns green in basic medium. Substances whose smell changes in acidic or basic solution are called OLFACTORY INDICATORS. Eg:- onion, vanilla and clove oil. 5. Solubility: All mineral acid are soluble in water in all proportion and conducts electricity in its aqueous solution. 6. Conductivity: All acids are good conductor of electricity in their aqueous state. CHEMICAL PROPERTIES OF ACIDS: 1. Reaction with active metals: Both dil. HCl and dil. H2SO4 reacts explosively with active metals like Na, K and Ca. Hence these metals are not used for the preparation of hydrogen. Metals like Mg, Zn, Fe reacts with dil. HCl or dil. H2SO4 to give corresponding metallic salt and hydrogen. Mg + 2HCl Zn + H2SO4 Fe + 2HCl MgCl2 + H2 ZnSO4 + H2 FeCl2 + H2 Observation: Brisk effervescence takes place due to evolution of colourless, odourless gas hydrogen which burns with a pop sound when a burning splinter is brought near to it. In the reaction between iron and dil. HCl or dil. H2SO4, Fe2+ is always form and not Fe3+ salt. It is because the hydrogen formed in the reaction acts as a reducing agent which reduces Fe 3+ formed (if any) into Fe2+ salt. 2FeCl3 + H2 2FeCl2 + 2HCl Nitric acid (both dilute and concentrated) and Conc. H2SO4 is not used to prepare hydrogen from metals as these acids are strong oxidising agents which oxidises the hydrogen formed during the reaction into water and thus defects the purpose of the reaction. 6|Page Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes Very dil.HNO3 (1% conc.) when reacts with Mg or Mn produces hydrogen. It is because on dilution oxidising power of nitric acid decreases. Mg + 2HNO3 Mg(NO3)2 + H2 (1% conc.) Mn + 2HNO3 Mn(NO3)2 + H2 (1% conc.) 2. Reaction with bases: When an acid react with a base to form salt and water only, the reaction is called neutralisation reaction. The heat liberated during neutralisation reaction is called heat of neutralisation. CuO + H2SO4 CuSO4 + H2O NaOH + HCl NaCl + H2O Mg(OH)2 + 2HNO3 Mg(NO3)2 + 2H2O 3. Reaction with carbonates and bicarbonates: Metal carbonates and bicarbonate on treatment with dil. acids, liberates CO2 (g) along with corresponding metallic salt and water. CaCO3 + 2HCl CaCl2 + H2O + CO2 Na2CO3 + H2SO4 Na2SO4 + H2O + CO2 NaHCO3 + HNO3 NaNO3 + H2O + CO2 Ca(HCO3)2 + 2HCl CaCl2 + 2H2O + 2CO2 Observation: Brisk effervescence takes place due to evolution of colourless, odourless gas CO2 which turns lime water milky but has no effect on i) KMnO4 solution i.e. pink or purple colour KMnO4 solution remains unchanged. C.T. ii) Acidified K2Cr2O7 solution i.e. orange colour of acidified K2Cr2O7 remains orange. The carbon dioxide gas liberated turns limewater (Ca(OH)2) milky due to formation of CaCO3, the milkiness disappears when excess of carbon dioxide gas is pass through it due to the formation of Ca(HCO 3)2. CO2 + Ca(OH)2 CaCO3 + H2O (lime water) (milkiness) CaCO3 + H2O + CO2 (excess) Ca(HCO3)2 (colourless solution) If the salt produced is insoluble, then the reaction does not proceed. So, we do not expect PbCO3 to react with HCl or H2SO4. Nor does CaCO3 react with H2SO4. 7|Page Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes 4. Reaction with sulphites and bisulphites: Metal carbonates and bicarbonate on treatment with dil. acids, liberates CO2 (g) along with corresponding metallic salt and water. CaSO3 + 2HCl CaCl2 + H2O + SO2 Na2SO3 + H2SO4 Na2SO4 + H2O + SO2 Na2SO3 + 2HCl 2NaCl + H2O + SO2 NaHSO3 + HNO3 NaNO3 + H2O + SO2 Ca(HSO3)2 + 2HCl CaCl2 + 2H2O + 2SO2 Observation: A colourless gas having the smell of burning sulphur i.e. SO2 (g) is liberated which turns lime water milky and turns: i) Pink or purple colour KMnO4 solution into colourless. 2KMnO4 + 2H2O+ 5SO2 (Pink or purple) K2SO4 + 2MnSO4 + 2H2SO4 (colourless) C.T. ii) Acidified K2Cr2O7 solution from orange to clear green due to formation of Cr2(SO4)3. K2Cr2O7 + H2SO4 + 3SO2 K2SO4 + Cr2(SO4)3 + H2O (orange) (green) MI*: In the above two reactions SO2 acts as a reducing agent. The sulphur dioxide gas liberated turns limewater (Ca(OH) 2) milky due to formation of CaSO3, the milkiness disappears when excess of sulphur dioxide gas is pass through it due to the formation of Ca(HSO3)2. SO2 + Ca(OH)2 CaSO3 + H2O (lime water) (milkiness) CaSO3 + H2O + SO2 Ca(HSO3)2 (excess) (colourless solution) MI*: 1. Lime water test cannot be used to distinguish between CO 2 and SO2 as both turns it milky and on passing both the gas in excess to the milky solution, the milkiness of it disappears. 2. Both CO2 and SO2 gas turns moist blue litmus red showing that they are acidic in nature. But SO2 further changes the red colour of the litmus into colourless due to its bleaching action. 3. The bleaching action of SO2 is temporary in nature. 8|Page Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes 5. Reaction with sulphides: Metal sulphides on reaction with dil acids like HCl, H 2SO4, etc., corresponding metal salts are formed with the liberation of colourless gas having the foul smell of rotten eggs i.e. H 2S. Na2S + 2HCl 2NaCl + H2S PbS + 2HNO3 FeS + 2HCl ZnS + H2SO4 Pb(NO3)2 + H2S FeCl2 + H2S ZnSO4 + H2S Observation: Colourless gas having the foul smell of rotten eggs i.e. H2S is formed which turns: i) Purple or pink colour of KMnO4 into colourless. C.T. ii) Moist lead acetate paper/filter paper dipped in Pb(NO3)2 solution from colourless to silvery black. Pb(CH3COO)2 + H2S (Lead acetate) PbS + 2CH3COOH (silvery black ppt.) Pb(NO3)2 + H2S PbS +2HNO3 (silvery black ppt.) 6. Reaction with nitrates: Nitrates do not react with dil. acids. However , Pb(NO3)2 solution reacts with both dil. HCl or dil. H2SO4 to form insoluble lead salts. Pb(NO3)2 + 2HCl PbCl2 + 2HNO3 (white ppt.) The PbCl2 formed is soluble in hot water but insoluble in cold water. Pb(NO3)2 + H2SO4 PbSO4 + 2HNO3 (white ppt.) The PbSO4 formed is insoluble in water. AgNO3 solution reacts with dil. HCl to form curdy white ppt. of AgCl which is soluble only in excess of NH4OH solution to form a colourless solution of diamminesilver (I) chloride. AgNO3 + HCl AgCl + HNO3 (Curdy white ppt.) AgCl + 2NH4OH [Ag(NH3)2]Cl + 2H2O Diamminesilver (I) chloride (colourless soln) When the colourless solution of diamminesilver (I) chloride is shaked with HNO3, curdy white ppt. of silver chloride is restored. 9|Page Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes DEGREE OF DISSOCIATION/IONISATION ( ) The degree of dissociation (also known as degree of ionization), is a way of representing the strength of an acid. It is defined as the ratio of the number of ionized molecules and the number of molecules dissolved in water. = Acids having degree of ionisation: i) Above 30% are strong acids. ii) Below 30% are weak acids. iii) Rest are moderate acids, at a specified molar concentration. Q) What do you understand by the statement that degree of Ionisation of acetic acid is 20%? Ans: It means that out of 100 molecules of acetic acid only 20 molecules ionise completely into ions and rest remains as unionised molecules. Hence acetic acid is a weak acid. BASES: A base is either a metallic oxide or a metallic hydroxide or ammonium hydroxide which reacts with hydronium ion of acid to form salt and water only. CuO + H2SO4 CuSO4 + H2O NaOH + HCl NaCl + H2O Al(OH)3 + 3HNO3 Al(NO3)3 + 3H2O Mg(OH)2 + H2SO4 MgSO4 + 2H2O NH4OH + HCl NH4Cl + H2O BASIC OXIDE: A metallic oxide which contains O2- ion and reacts with an acid to form salt and water only. BASIC HYDROXIDE A metallic hydroxide which contains OH- ion and reacts with an acid to form salt and water only. 10 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes MI*: If word only is omitted from the above definition, certain compounds, which are quite different from basic metallic oxides and hydroxides, would be included in the definition of the base. For e.g.: MnO2 is a metallic oxide which reacts with hydrochloric acid to give MnCl2 (a salt) and water, but the word only excludes it from the class of bases, because chlorine is also produced. MnO2 + 4HCl (Black) (Conc.) MnCl2 + 2H2O + Cl2 (mounds brown) (greenish yellow) The chlorine gas produced ,has greenish yellow in colour and turns moist blue litmus paper into red showing Cl2 is an acidic gas and then turns the red colour of litmus into white due to its bleaching action which is permanent in nature. C.T. The chlorine gas turns moist starch iodide paper blue black. 2KI + Cl2 2KCl + I2 Starch + I2 blue-black colour ALKALIS: An alkali is a water-soluble base which produces OH - ion as the only negatively charged ion when dissolved in water. ( ) + All alkalis are bases but all bases are not alkalis. This is because all bases are not soluble in water but all alkalis are soluble in water. All metallic oxides and hydroxides are insoluble except of sodium, potassium and calcium (slightly soluble). Soluble bases (alkalis) Na2O, K2O, NaOH, KOH, Ba(OH)2, Ca(OH)2, NH4OH, etc. Insoluble bases (not alkalis) CuO, PbO, Fe(OH)2,Fe(OH)3, Al(OH)3, Cu(OH)2, etc. 11 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes CLASSIFICATION OF BASES (ALKALIS) Bases are classified on the bases of : 1. Strength: Strength of the base depends on the concentration of OH- ion in its aqueous solution. More the OH- ion in the aqueous solution more will be the strength of the base. According to the strength bases are classified into two types: Strong base Alkalis which undergoes complete dissociation in aqueous solution to produce high concentration of OHare called strong alkalis. Weak base Alkalis which undergoes only partial dissociation or ionisation in aqueous solution to produce low concentration of OH- are called weak alkalis. e.g.: NaOH, KOH, Ba(OH)2, etc. e.g.: NH4OH, Ca(OH)2, etc. 2. Concentration: It depends upon the amount of alkali present in its aqueous solution. More the amount of alkali relative to water more will be its concentration. On dilution concentration of an alkali decreases. According to concentration, alkali are classified into two types: Concentrated alkali Dilute alkali The aqueous solution of a base The aqueous solution of a base which contain less amount of which contain more amount of water then alkali is called water then alkali is called dilute concentrated alkali. alkali. 3. Acidity Acidity of a base is defined as the number of hydroxyl ions ( ) which can be produced per molecule of base in aqueous solution. ( ) + ( ) + OR The number of hydrogen ions of an acid with which a molecule of that base will react to produce salt and water only is known as acidity of the base. ( ) + + 12 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes For water-insoluble hydroxides, acidity is equal to number of replaceable ions in one molecule of that base. According to acidity, bases are classified into three types: Type of base Monoacidic base Diacidic base Triacidic base Definition Dissociation in aq. or fused state ( ) + Base which dissociates in molten or aqueous ( ) + state to produce one ion per molecule ( ) + of that base. Eg; NaOH, KOH and NH4OH Base which dissociates ( ) ( ) + in molten or aqueous state to produce two ( ) ( ) + ion per molecule of that base. Eg; Ca(OH)2, Cu(OH)2, etc. ( ) + Base which dissociates in molten or aqueous state to produce three ion per molecule of that base. Eg; Al(OH)3, Fe(OH)3 PREPARATION OF BASES 1. From metals: Active metal when react with oxygen give bases. 4Na + O2 2Na2O 2Mg + O2 2MgO 2. By the action of water on reactive metals: Metals like sodium, potassium and calcium reacts with cold water to give corresponding soluble metal hydroxide and liberates H 2 gas. 2Na + 2H2O 2NaOH + H2 2K + 2H2O 2KOH + H2 Ca + 2H2O Ca(OH)2 + H2 13 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes 3. By the action of water on soluble metallic oxides: Metal oxides of potassium, sodium and calcium reacts with water to give soluble metal hydroxide. Na2O + H2O 2NaOH K2O + H2O 2KOH CaO + H2O Ca(OH)2 In the above reactions a soluble base is prepared from another soluble base. 4. By double displacement: Aqueous solution of salts with a base(alkali) precipitate the respective metallic hydroxide. The colour of the insoluble metal hydroxides helps to identify the cation present in them or the salt taken. FeCl3 + 3NaOH Fe(OH)3 + 3NaCl (Reddish brown ppt) FeCl2 + 2NaOH Fe(OH)2 + 2NaCl (Dirty green ppt) CuSO4 + 2NaOH Cu(OH)2 + Na2SO4 (Pale blue ppt) Pb(NO3)2 + 2NH4OH Pb(OH)2 + 2NH4NO3 (Chalky white ppt) In the above reactions an insoluble base is prepared from soluble base. 5. By the action of oxygen on metal sulphides: On heating metal sulphides in the presence of oxygen produces metal oxides which are the bases along with the SO2 gas. This process is called roasting. 2ZnO + 2SO2 2PbO + 2SO2 2ZnS + 3O2 2PbS + 3O2 6. By the decomposition of salts: i) Decomposition of metal carbonate: On heating metal carbonates in the absence of oxygen produces metal oxides which are the bases along with the CO2 gas. This process is called calcination. CuCO3 (light green) CuO + CO2 (black) CaCO3 CaO + CO2 (white amorphous) (white) 14 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes Na2CO3 and K2CO3 do not decompose on heating as they are refractory in nature i.e., they can withstand high temperature. ii) Decomposition of metal nitrate: On heating metal nitrate, they decompose to give corresponding metal oxides (base) along with the liberation of NO2 and O2 gases. 1) 2Pb(NO3)2 2PbO + 4NO2 + O2 Observation: On strong heating Pb(NO3)2 decrepitates and give reddish brown gas NO2, leaving behind a residue of PbO which is black when hot and yellow when cools. 2) 2Zn(NO3)2 2ZnO + 4NO2 + O2 Observation: On strong heating Zn(NO3)2 decomposes to give reddish brown gas NO2, leaving behind a residue of ZnO which is yellow when hot and white when cools. 3) 2Cu(NO3)2 2CuO + 4NO2 + O2 Observation: On strong heating Cu(NO3)2 decomposes to give reddish brown gas NO2, leaving behind a black residue of CuO. MI*: 1. Nitrates of sodium and potassium does not give metal oxides (base) on thermal decomposition rather they give corresponding nitrites along with oxygen gas. 2NaNO3 2KNO3 2NaNO2 + O2 2KNO2 + O2 2. Nitrates of silver and mercury reduces to corresponding metals on heating and hence they do not give metallic oxide (base). 2AgNO3 Hg(NO3)2 2Ag + 2NO2 + O2 Hg + 2NO2 + O2 7. Ammonia hydroxide can be prepared by simply dissolving ammonia gas in water, as ammonia is highly soluble in water. NH3 (g) + H2O NH4OH(aq) (weak alkali) 15 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes PHYSICAL PROPERTIES OD BASES/ALKALIS 1. They have sharp and bitter taste. 2. They show mild corrosive action to skin. 3. They change the colour of indicators. Indicator Litmus Methyl orange Phenolphthalein Alkaline Phenolphthalein Colour change in basic medium Red to Blue Orange to Yellow Colourless to Pink Pink remains pink MI*: Insoluble bases do not affect indicators. 4. They are slippery to touch. It is because strong alkalis like NaOH and KOH react with the oil (in the form of fat) present in our skin to form soapy solution, which is slippery to touch. CHEMICAL PROPERTIES 1. With carbon dioxide: Strong alkalis absorb carbon dioxide from air to form carbonates. It is because of this reason white deposits of sodium carbonate or potassium carbonates are formed at the neck of reagent bottles in which NaOH or KOH is stored. 2NaOH + CO2 2KOH + CO2 Na2CO3 + H2O K2CO3 + H2O 2. With acids: They show neutralisation reaction with bases. NaOH + HCl NaCl + H2O Mg(OH)2 + 2HNO3 Mg(NO3)2 + 2H2O Fe(OH)2 + H2SO4 FeSO4 + 2H2O 3. With ammonium salts: When alkali are warmed with ammonium salts, ammonia gas is given out. NH4Cl + NaOH NaCl + H2O + NH3 CaCl2 + 2H2O + 2NH3 K2SO4 + 2H2O + 2NH3 2NH4Cl + Ca(OH)2 (NH4)SO4 + 2KOH C.T. When a glass rod dipped in HCl brought near to the ammonia, dense white fumes of NH4Cl is formed. HCl + NH3 NH4Cl (dense white fumes) The above test is the confirmatory test for ammonia. 16 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes IONIC PRODUCT OF WATER (KW) Pure water ionises to very small extent as + At equilibrium, + [ ] KC = [ ] KC [ ] = + [ ] KW = + [ ] (KW= KC [ ]) At 25 C, it was observed that [ ] = [ ] = KW = = On adding acid to water, the concentration of ( ) ions increases i.e. acidic nature increases and that of decreases so that KW remains same and if alkali is added, the reverse is noticed. So, the nature of solution depends upon the concentration of ( ) in the solution In 1909 a Danish biochemist Sorensen devised a scale known as pH scale which represents the ( ) ion concentration of the given aqueous solution. The p in pH stands for Potenz in German meaning power, so pH means the power of hydrogen. The pH of a solution is the negative logarithm to the base 10 of the hydrogen ion concentration expressed in moles per litre. = [ ] 17 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes If pH = 7, the solution is neutral in which [ ] = [ ] If pH > 7, the solution is alkaline in which [ ] < [ ] If pH < 7, the solution is acidic in which [ ] > [ ] Universal indicator: It is a mixture of organic dyes that gives definite colour changes over a wide range of pH. Solutions containing a drop of the universal indicator is matched against a standard colour chart to find the pH. The universal indicator not only differentiates better the acidic and basic nature of solutions, it also indicates the strength of the solution. Universal indicator produces green colour in a neutral solution, i.e., when pH = 7. It changes in a basic solution progressively from blue to indigo to violet as pH increases from 7 to 14. The colour change in acidic solution is from yellow to pink, and then to red, as pH decreases from 7 to 1. Difference between acid-base indicator and universal indicator Acid-base indicator Universal indicator Common acid-base indicators Universal indicator is a mixture such as litmus, methyl orange of organic dyes that gives and phenolphthalein are definite colour changes over a single compounds. The wide range of pH. change in their colour is abrupt at a particular pH. These can distinguish It can distinguish between an between acidic and basic acidic and basic solution and at solutions but cannot the same time it can also determine the strength of indicate the strength of the the solutions. solution. They do not help to Then can be used to distinguish distinguish between solutions between the solutions of of different pH values. different pH values. IMPORTANCE OF pH IN EVERYDAY LIFE 1. Acid rain : If pH is less than 5.6 of rain water it is said to be acid rain. This water contains acids like sulphuric acid, nitric acid and carbonic acid which are formed by atmospheric pollutants mainly SO 2 and oxides of nitrogen. Acid rain reduces fertility of soil, destroys marine life and causes damage to monuments. 18 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes 2. In digestive system :Hydrochloric acid is produced in the stomach which helps in the digestion of food but if it becomes excess, the pH falls, and pain and irritation occurs, to get rid of this ANTACIDS like milk of magnesia (Mg(OH)2) is generally used to adjust the pH. 3. In preventing tooth decay : Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth enamel, made up of calcium phosphate is the hardest substance in the body. It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. The best way to prevent this is to clean the mouth after eating food. Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay. 4. In agriculture : Plants require a specific pH of the soil for their proper growth. Plants cannot grow in too alkaline or too acidic soils. Therefore, for proper cultivation of crops it is important to have knowledge of the pH of the soil. For e.g., rice grows better in slightly acidic soil, sugarcane in neutral soil and citrous fruits in alkaline soil. If the soil is too acidic then its pH can be raised by adding lime (or slaked lime) which neutralizes the excess acid in the soil. This process is called Liming. 5. Existence of living beings : Organisms require a specific pH for their ideal growth and development. In the human body, all the physiological reactions take place in the pH of 7-7.8. if the pH changes by 0.2 pH units, death results. 6. Food preservative : A change in pH of milk from 6.6 indicates that milk has turned sour. A milkman adds a small amount of baking soda to fresh milk to prevent acidification of milk. By adding a small amount of baking soda, the milkman shifts the pH of the fresh milk from 6.6 to slightly alkaline so that he can keep it for a longer time as the milk in alkaline condition, does not set curd easily. 7. In medicines : Certain diseases are diagnosed only on the basis of the pH value of the blood and urine. 19 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes APPLICATION OF NEUTRALISATION 1. Bee-sting leaves an acid (formic acid) which cause pain and irritation. Use of a mild base like baking soda or soap solution on the stung area neutralise the acid and gives relief. 2. Stinging hair of nettle leaves inject methanoic acid (formic acid) causing burning pain. Use of baking soda or soap solution on the stung area neutralise the acid and gives relief. 3. Wasp stings are basic in nature. When a wasp bites, basic substance is injected into the skin. This can cause pain and swelling. This effect on the skin can be nullified or neutralised by rubbing mild acid like vinegar (which contains acetic acid) on the affected area. 4. Astronauts in spaceships use lithium hydroxide to neutralise danger level of exhaled carbon dioxide. 2LiOH + CO2 Li2CO3 + H2O 5. In descaling kettles: On boiling hard water, calcium carbonate (lime scale) gets deposited in kettles. This lime scale can be removed by neutralisation with an acid that is strong enough to neutralise calcium carbonate, but not strong enough to damage the metal. Thus, vinegar (acetic acid) or formic acid can be used to descale kettles. 6. In Hair Conditioning : Shampoos which we use on our hair contain alkaline substances. This can cause scales on hairs which makes it unmanageable. In order to solve this, we use hair conditioners. Hair conditioners contain acidic substances which can neutralise the alkali, and as a result, it helps the scales to close up. SALTS: A salt is a compound formed by the partial or total replacement of the ionisable hydrogen atoms of an acid by a metallic ion or an ammonium ion. Partial replacement NaNO3 + H2SO4 Conc. Complete replacement NaNO3 + H2SO4 Conc. NaHSO4 + HNO3 (acid Salt) Na2SO4 + 2HNO3 (Salt) 20 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes Ionic definition of salt: Salt is an ionic compound, which dissociates in water to yield a positive ion other than hydrogen ion (H+) and a negative ion other than hydroxyl ion (OH-). Na+ NaCl Cl- + Positive ion Negative other than ion but not hydrogen hydroxyl CLASSIFICATION OF SALTS Salts are classified into six types: Acid salt Normal salt SALTS Complex salt Double salt Basic salt Mixed salt Normal salt : Those salts which are formed by complete replacement of ionisable hydrogen atoms of an acid by a metallic ion or ammonium ion, are called normal salts. HCl + NaOH NaCl + H2O H2SO4 + 2NaOH Na2SO4 + 2H2O H2SO4 + 2NH4OH (NH4)2SO4 + 2H2O Normal salts do not exhibit the properties of an acid in solution. Acid salt : Acid salts are formed by partial replacement of the ionisable hydrogen atoms of a polybasic acid by a metal or an ammonium ion. NaNO3 + H2SO4 Conc. OR NaOH + H2SO4 dil. NaHSO4 + HNO3 (acid Salt) NaHSO4 + H2O (acid Salt) 21 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes Acid salts are usually formed when the amount of base taken is insufficient for the complete neutralisation of the acid. Acid salts ionise in aqueous solutions yielding H3O+ ion or H+(aq) ion. Hence aqueous solutions of acids exhibit all the properties of acid. NaHSO4 Na+ + HSO HSO H+ + S NaH2PO4 Na+ + H2PO H2PO H+ + HP HP H+ + P Monobasic or monoprotic acids do not form any acid salt since they contain only one replaceable hydrogen ion. A dibasic salt can form two types of salt, one is acid salt and another is normal salts. Similarly, a tribasic salt can form three salts, i.e., a normal salt and two acid salts. For dibasic acid: H2SO4 + NaOH NaHSO4 + H2O (Acid Salt) NaHSO4 + NaOH Na2SO4 + H2O (Normal salt) For tribasic acid: H3PO4 + NaOH NaH2PO4 + H2O (Acid salt) NaH2PO4 + NaOH Na2HPO4 + H2O (Acid salt) Na2HPO4 + NaOH Na3PO4 + H2O (Normal salt) Examples of acid salts : NaHSO4, NaHSO3, NaHCO3, NaH2PO4, Na2HPO4, KHSO3, etc. Health salts : These are the mixtures of dry citric acid or tartaric acid and sodium hydrogen carbonate(an acid salt). On adding water, acid reacts with NaHCO3 to liberate CO2 which forms an effervescent drink and relieves gas pressure in the stomach. 22 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes Basic salts : Basic salts are formed by the partial replacement of the hydroxyl group of a di-acidic or a tri-acidic base by an acid radical. Pb(OH)2 + HCl Pb(OH)Cl + H2O (Basic salt) Mg(OH)2 + HCl Mg(OH)Cl + H2O (Basic salt) These salts on neutralisation with acids yields normal salts. Mg(OH)Cl + HCl (Basic salt) MgCl2 + H2O (Normal salt) *Double salts : These salts are formed by the union of two simple salts that dissolve in water and crystallise. These salts are stable in stable in solid state but lose their identity in solution. For example, Potash alum (K2SO4.Al2(SO4)3.24H2O) exists in solid state but dissociates in solution giving K+, Al3+ and S ions. Examples of double salts : Potash alum (K2SO4.Al2(SO4)3.24H2O), Mohr s salt (FeSO4.(NH4)SO4.6H2O), Dolomite (CaCO3.MgCO3), etc. *Mixed salt : Salts that contain more than one basic or acid radical are called mixed salts. Eg: sodium potassium carbonate (NaKCO3),Bleaching powder (CaOCl2). NaKCO3 Na+ + K+ + C (Two basic radical) CaOCl2 Ca2+ + ClO- + Cl(Two acid radical) *Complex salts : Complex salts are those which on dissociation give one simple ion and one complex ion. Eg: Na[Ag(CN)2], [Ag(NH3)2]Cl, K2HgI4, Na2ZnO2, [Cu(NH3)4]SO4, etc. [Ag(NH3)2]Cl [Ag(NH3)2]+ + Cl(complex ion) + (simple ion) Na[Ag(CN)2] Na + [Ag(CN)2]- (simple ion) (complex ion) 23 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes SOLUBILITY OF SALTS K+ Na+ Ba2+ Ca2+ Mg2+ Al3+ Zn2+ Fe2+ Fe3+ Mn2+ Pb2+ Cu2+ Ag+ Hg2+ S S S S S S S S S S S S S S S S S S S SP S S S S S S S S S S S S S S S S S S N S N N S S N SP S S S S S S N S N S S S S SP SP N N N N N N N - - S S N N N - N N - N N N N N S S N N N - N - N N N N N N S S N N N N N N N N N N N N S S N N N - N N N N N N N N S = soluble, SP = sparingly soluble, N = insoluble PREPERATION OF SALTS 1. Iron (III) chloride (FeCl3) : Method of preparation: Direct combination (synthesis) Procedure: A rust-free iron coil is placed inside a combustion tube and dry chlorine is passed through the tube to expel out air and moisture from the combustion tube. Chlorine is dried by passing through conc. Sulphuric acid (drying agent). The combustion tube is then slowly heated which results in the reaction of iron and chlorine. 24 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes Chemical reaction : 2Fe + 3Cl2 2FeCl3 (excess) The iron becomes red hot because reaction of iron and chlorine is highly exothermic. At this moment external heating is stopped. The vapours of volatile FeCl3 are condensed in a receiver flask connected to CaCl2 drying tube, where it condensed to form brown scales of FeCl3. FeCl3 is highly deliquescent, so it is kept dry with the help of fused Calcium Chloride (B) which prevents the entry of moisture from air. Anhydrous FeCl3 cannot be prepared by simply heating the hydrated ferric chloride (FeCl3.6H2O), because on heating FeCl3.6H2O produces Fe2O3.H2O and HCl. 2FeCl3.6H2O Fe2O3 + 9H2O + 6HCl Anhydrous Iron (III) chloride is used as a catalyst in certain reactions. Examples of other salts which can be prepared by direct combination or synthesis method are: 1. 2Al + 3Cl2 2. Fe + S 3. Zn + S 2AlCl3 FeS ZnS 2. Zinc (II) sulphate (or White vitriol) : Method of preparation: Simple Displacement. Procedure: Take dilute sulphuric acid in a beaker. Add to it zinc granules in excess. Warm slowly and stir till effervescence of hydrogen ceases. When effervescence ceases, it indicates that all the acid has been used up i.e. reaction is completed. The excess of zinc is filtered off. The filtrate is transferred to china dish. 25 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes Evaporate the solution (filtrate) to get white needle-shaped crystals of hydrated zinc sulphate. Chemical reaction : Zn + H2SO4 ZnSO4 + H2 ZnSO4 + 7H2O ZnSO4.7H2O Filter, wash them with water and dry them between the folds of filter paper. 3. Iron (II) sulphate/Ferrous sulphate (or Green vitriol) : Method of preparation: Simple Displacement. Procedure: Take dilute sulphuric acid in a beaker. Add to it iron fillings in excess. Warm slowly and stir till effervescence of hydrogen ceases. When effervescence ceases, it indicates that all the acid has been used up i.e. reaction is completed. The excess of Iron fillings are filtered off. The filtrate is transferred to china dish. Evaporate the solution (filtrate) to get pale green crystals of hydrated Iron (II) sulphate. Chemical reaction : Fe + H2SO4 FeSO4 + H2 FeSO4 + 7H2O FeSO4.7H2O 4. Copper (II) sulphate (or Blue vitriol) : Method of preparation: If CuO or Cu(OH)2 is used to react with dilute sulphuric acid then method of preparation is Neutralisation of insoluble base by an acid. If CuCO3 is used to react with dilute sulphuric acid then method of preparation is Decomposition of a salt by an acid. Procedure: Take dil. H2SO4 in a beaker. Add to it excess of black CuO(or blue copper hydroxide or greenish-blue copper carbonate). Heat slowly and stir. 26 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes Wait until the solution no longer turns blue litmus red. This indicates that the whole of acid has been neutralised. In case of CuCO3, wait until no more CO2 is given off. Filter the bluish green solution of CuSO 4 obtained to remove solid matter. Evaporate the filtrate in the evaporating dish to the crystallisation point. Allow the saturated solution to cool itself to get blue crystals of CuSO4.5H2O. Chemical reaction : CuO + H2SO4 CuSO4 + H2O Cu(OH)2 + H2SO4 CuSO4 + 2H2O CuCO3+ H2SO4 CuSO4 + H2O + CO2 CuSO4 + 5H2O CuSO4.5H2O Filter and dry the crystals between the folds of filter paper. 5. Lead (II) chloride : Method of preparation: Double displacement (Precipitation). Procedure: The reaction of PbO (or Pb(OH)2 or PbCO3) with direct dil. HCl is an impractical method of preparing lead chloride because an insoluble crust of lead chloride is formed on PbO (or Pb(OH)2 or PbCO3) which prevent further reaction. Hence at first PbO (or Pb(OH)2 or PbCO3) converted into soluble Lead nitrate by treating them with HNO3. The solution of Lead nitrate formed above is treated with HCl or NaCl to get heavy white ppt. of lead chloride which will be collected as residue on filtration. The lead chloride obtained is then washed repeatedly with cold water. The ppt. is taken in a china dish with some water and is heated till the ppt of Lead chloride dissolves. The solution is then cooled. Chemical reaction: PbO + 2HNO3 Pb(NO3)2 + H2O Pb(OH)2 + 2HNO3 Pb(NO3)2 + 2H2O PbCO3 + 2HNO3 Pb(NO3)2 + H2O + CO2 Pb(NO3)2 + 2HCl PbCl2 + 2HNO3 The white ppt PbCl2 soluble in hot water but insoluble in cold water. 27 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes Pure, needle shaped crystals of lead chloride are thus obtained. The chlorides of Pb2+, Ag+ and Hg+ and the sulphates of Ba2+, Pb2+ and Ca2+ are also prepared using this method (i.e. precipitation). For Eg, Preparation of Lead sulphate: PbCO3 + 2HNO3 Pb(NO3)2 + H2O + CO2 Pb(NO3)2 + H2SO4 PbSO4 + 2HNO3 The white ppt. PbSO4 insoluble in water. Direct addition of dil. H2SO4 to lead carbonate is an impractical method of preparing lead sulphate because an insoluble crust of lead sulphate is formed on lead carbonate which prevent further reaction. 6. Calcium carbonate (CaCO3) : Method of preparation: Double displacement (Precipitation). It is prepared by adding Na2CO3 solution to a hot solution of CaCl2 in a beaker, till the Na2CO3 is in excess. Chemical reaction : CaCl2 + Na2CO3 CaCO3 + 2NaCl The white ppt. of CaCO3 formed above is collected as a residue of filtration. The obtained ppt. is washed repeatedly with cold water and dried to obtain an amorphous powder of CaCO3. The carbonate of all the metals (except Na, K and N ) are prepared by this method. 7. Sodium bicarbonate (NaHCO3) : Prepare Sodium Carbonate Solution: Dissolve sodium carbonate (Na2CO3) in water to prepare a solution. Ensure the solution is well mixed. Cool the solution by keeping the flask in a freezing mixture. 28 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes Introduce Carbon Dioxide: Bubble carbon dioxide (CO2) gas through the sodium carbonate solution. This can be done by passing CO2 gas through a tube or directly bubbling CO2 into the solution. Chemical Reaction: The carbon dioxide reacts with the sodium carbonate solution, forming sodium bicarbonate (NaHCO 3) according to the following equation: Na2CO3 + CO2 + H2O 2NaHCO3 Crystals of NaHCO3 will ppt. out after sometime. Filter the crystals and dry it in the folds of filter paper. 8. Sodium sulphate or Glauber salt (Na2SO4.10H2O) : Method of preparation: Neutralisation of soluble base by an acid (titration). This method is used for preparing the soluble salts of only sodium, potassium and ammonium. Since the reactants as well as the products are soluble, a titration is conducted to determine the completion of the neutralisation reaction. The reaction of NaOH with dil. H2SO4 is a neutralisation reaction. Hence, an indicator is used to determine the completion of the reaction. Procedure: Dil. Sulphuric acid is filled in a burette upto the 0 cm3 mark. About 25 cm3 of NaOH is pipetted out into a conical flask. The sodium hydroxide is made pink by adding a few drops of phenolphthalein. The acid is added dropwise from the burette into the alkali with constant stirring until the pink colour just changes to colourless. The base has now been neutralised. This is the end point. Measure the volume of acid used for neutralisation, from the reading on the burette. 29 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR) THE CAREER NR Classes Repeat the process, this time without adding indicator. Run the measured volume of the acid from the burette, into the 25 cm 3 of alkali in the flask. Evaporate off most of the water from the solution, over a water bath. Cool the saturated solution to get the crystals. Dry off the crystals on filter paper Chemical reaction: 2NaOH + H2SO4 Na2SO4 + 10H2O Na2SO4 + 2H2O Na2SO4.10H2O HYDROLYSIS OF SALTS Hydrolysis of a salt may be defined as the interaction of ions of a salt with oppositely charged ions of water to give acidic or basic solution. Consider the hydrolysis of a general salt AB Dissociation of salt: Dissociation of water: + + + (base) + (acid) If the product formed due to hydrolysis of salt contain a strong acid and a weak base, the solution is acidic and turns blue litmus red. The salt is called acidic salt. If the product formed due to hydrolysis of salt contain a strong base and a weak acid, the solution is alkaline or basic and turns red litmus blue. The salt is called basic or alkaline salt. For Eg: 1. CuSO4 on hydrolysis gives Cu(OH)2 (a weak base) and H2SO4 (a strong acid). Hence CuSO4 (a normal salt) is an acidic salt having pH less than 7. CuSO4 + 2H2O A.S. Cu(OH)2 + H2SO4 W.B. S.A. 2. Baking soda (NaHCO3) on hydrolysis gives NaOH (a strong base) and H2CO3 (a weak acid). Hence NaHCO3 (an acid salt) is basic in nature having pH more than 7. NaHCO3 + H2O NaOH + H2CO3 B.S. S.B. W.A Hydrolysis does not occur in salts formed from strong acids and strong bases and the aqueous solution of salt of strong acids with strong bases are neutral. Eg; NaCl,KCl,NaNO3,KNO3, etc. 30 | P a g e Acids, Bases & Salts by Nilamadhav Rath (NR)

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

Formatting page ...

 

  Print intermediate debugging step

Show debugging info


 

 

© 2010 - 2025 ResPaper. Terms of ServiceContact Us Advertise with us

 

seetalsharmavermamallick chat