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acid bases and salt

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Acids, Bases, and Salts 1. Acid : A compound which on dissolving in water furnishes proton [hydrogen ion (H+)] as the only positively charged ion is called an acid. or A compound which on dissolving in water furnishes hydronium ion as only positively charged ion is called an acid. 2. Organic acid : An acid derived from an animal or vegetable origin is called organic acid, e.g., formic acid; acetic acid; citric acid; tartaric acid, etc. 3. Mineral acid : An acid derived from minerals is called mineral acid, e.g., HCl, H2SO4, HNO3, HBr, etc. 4. Basicity of an acid : The number of hydrogen ions [H+ (aq)], which can be produced by one molecule of an acid on complete ionisation is called basicity of the acid. 5. Monobasic acid : When one molecule of an acid on complete ionisation produces one hydrogen ion [H+ (aq)] then the acid is said to be monobasic, e.g., HCl, HNO3, HBr, HI, HCOOH, CH3COOH. 6. Dibasic acid : When one molecule of an acid on complete ionisation produces two hydrogen ions [H+ (aq)] then the acid is said to be dibasic, e.g., : H2SO4, H2SO3, H2CO3, (COOH)2, H2S. 7. Tribasic acid : When one molecule of an acid on complete ionisation produces three hydrogen ions [H+ (aq)], then the acid is said to be tribasic, e.g., : H3PO4, H3PO3. 8. Strength of an acid : The degree of dissociation of an acid in aqueous solution is called strength of an acid. No. of acid molecules ionised Degree of dissociation = 100. No.of molecules of acid in solution 9. Strong acids : The acids which undergo almost complete ionisation (more than 30%) in an aqueous solution, thereby producing high concentration of H+ (aq) ions, are called strong acids, e.g., HNO3, HCl and H2SO4. 1 Key Points 10. Weak acids : The acids which undergo partial dissociation in an aqueous solution (less than 30%), thereby producing low concentration of H+ (aq) ions, are called weak acids. e.g., H2CO3, H2SO3, H2S, HI, HCN, CH3COOH, HCOOH. 11. Concentration of an acid : It is the measure of amount of water present in an acid. 12. Concentrated acid : An acid which contains very little or no water is called concentrated acid. 13. Dilute acid. : An acid which contains large amount of water is called dilute acid. Generally speaking, if concentration of an acid is 1 mole/litre of water or less, it is called dilute acid. 14. Hydracid : An acid which contains hydrogen and a non-metallic element, other than oxygen is called hydracid. eg., : HCl; HBr; HI; HF; HCN; H2S. 15. Oxyacid : An acid which contains oxygen, along with hydrogen and one more non-metallic element is called oxyacid. e.g., : HNO3, HNO2, H2SO4, H2SO3, H3PO4, H3PO3, H2CO3. 16. Volatile acid : An acid which easily changes into its vapours below 100 C is called volatile acid. 17. Methods of preparation of Acids : (a) By synthesis or direct combination : Sunlight 2HCl H2 + Cl2 (b) By action of non-metallic oxides on water : H2O + SO2 H2SO3 (c) By displacement of more volatile acid by less volatile acid from a salt : Heat 2NaCl + H2SO4 (conc.) Na2SO4 + 2HCl (d) By the oxidation of non-metals : Boiling S + 6HNO3 H2SO4 + 2H2O + 6NO2 2 Key Points 18. Physical properties of Acids : 1. Acids have a sharp sour taste in an aqueous solution. 2. Acid turn blue litmus red, methyl orange solution pink and phenolphthalein solution colourless. 3. Strong acids have corrosive action on the skin. 19. Chemical properties of Acids : 1. Acids react with oxides and hydroxides of metals to form salt and water only. CuO + H2SO4 CuSO4 + H2O 2NaOH + H2SO4 Na2SO4 + 2H2O 2. Acids react with metallic carbonates to form salt, carbon dioxide and water. CaCO3 + 2HNO3 Ca(NO3) 2 + CO2 + H2O 3. Acids react with metallic sulphites to form salt, sulphur dioxide and water. Na2SO3 + 2HCl 2NaCl + SO2 + H2O 4. Acids react with active metals to form salt and hydrogen. Zn + dil. H2SO4 ZnSO4 + H2 20. Base : A compound which reacts with H+ (aq) ions of an acid to form salt and water as the only products is called base. 21. Alkali : An alkali is a compound which on dissolving in water furnishes OH ions as only negative ions. 22. Acidity of a base : The number of H+ (aq) ions of an acid, which will react completely with one molecule of a base, to form salt and water as the only products is called acidity of base. 23. Monoacidic base : When one H+ (aq) ion of an acid, reacts completely with one molecule of a base, to form salt and water as the only products, then base is said to be monoacidic, e.g., NaOH; KOH; NH4OH. 24. Diacidic base : When two H+ (aq) ions of an acid, react completely with one molecule of a base, to form salt and water as the only products, then base is said to be diacidic, e.g., Ca(OH)2, Zn(OH)2, Fe(OH)2. 3 Key Points 25. Triacidic base : When three H+ (aq) ions of an acid, react completely with one molecule of a base, to form salt and water as the only products, then the base is said to be triacidic, e.g., Al(OH)3, Fe(OH)3, Cr(OH)3. 26. Strong base : A base which almost completely dissociates in water, to produce high concentration of hydroxyl ions (OH ) is called strong base, e.g., : NaOH, KOH, LiOH, Ba (OH)2. 27. Weak base : A base, which undergoes partial dissociation in water, and produces low concentration of hydroxyl ions, is called a weak base. eg., : NH4OH, Mg (OH)2, Ca(OH)2. 28. General methods for the preparation of bases : 1. By the action of oxygen on metals : 2Mg + O2 2MgO 2. By the action of water or steam on active metals : 2Na + 2H2O 2NaOH + H2 3. By the action of water on soluble metallic oxides : CaO + H2O Ca(OH)2 4. By dissolving ammonia gas in water : NH3 + H2O NH4OH. 5. By treating soluble salts of metals with caustic alkali solution : AlCl3 + 3NaOH Al(OH)3 + 3NaCl 6. By the action of heat on metallic carbonates : heat CaCO3 CaO + CO2 7. By the action of heat on metallic nitrates : heat 2PbO + 4NO2 + O2 2Pb(NO3)2 4 Key Points 29. General properties of soluble alkalis : 1. Alkalis have a bitter taste and a soapy touch. 2. Alkalis turn (i) red litmus solution blue (ii) methyl orange solution colourless (iii) phenolphthalein solution pink (iv) turmeric solution brown. 3. Alkalis react with acid to form salt and water as the only products. NH4OH + HCl NH4Cl + H2O 4. Alkalis react with ammonium salts to liberate ammonia gas. 2NH4Cl + Ca(OH)2 CaCl2 + 2NH3 + 2H2O 5. Alkalis react with carbon dioxide to form carbonates. Ca(OH)2 + CO2 CaCO3 + H2O 6. Alkalis react with soluble salts of metals (except sodium and potassium salts), to form their insoluble hydroxides. CuCl2 + 2NaOH Cu(OH)2 + 2NaCl 30. Neutralisation : The chemical reaction in which hydronium ions (H3O+) derived from an acid and hydroxyl ions (OH ) derived from a base, combine to form unionised water molecules, is called neutralisation. 31. Salt : An ionic compound, containing a positive ion other than hydrogen ion and negative ion other than hydroxyl ion, is called salt. 32. Normal salt : A salt formed by the complete replacement of replaceable hydrogen ions of an acid, by a basic radical is called normal salt, e.g., : Na2SO4, KCl, KNO3, etc. 33. Acid salt : A salt formed by the partial replacement of replaceable hydrogen ions of an acid, by basic radical is called acid salt, e.g., : KHSO4, NaHSO3, Ca(HSO4)2, etc. 34. Basic salt : A salt formed by the incomplete neutralisation of base with an acid is called basic salt, e.g., : Cu(OH) Cl. 35. Double salt : A salt produced by the crystallisation of two simple salts from a mixture of their saturated solution is called double salt, e.g., K2SO4 . Al2 (SO4)3 . 24 H2O (Potash Alum), CaCO3. MgCO3 (Dolomite). 5 Key Points 36. Mixed salt : A salt which contains two or more acidic or basic radicals (except H+ (aq) and OH 1) is called mixed salt, e.g., : NaKSO4, Na2KPO4. 37. Complex salt : A double salt which on dissolving in water furnishes one simple and complex ion is called complex salt, e.g., NaAg CN)2, K3Fe(CN)6. 38. Hydrolysis : The phenomenon due to which a salt of strong acid and weak alkali or a salt of weak acid and strong alkali, on dissolving in water reacts with it to form parent alkali, so that the whole solution is either acidic or alkaline is called hydrolysis. For example, ZZ X 2NH4OH + H2SO4 (NH4)2SO4 + 2H2O YZZ Weak alkali Strong acid ZZ X 2NaOH + H2CO3 Na2CO3 + 2H2O YZZ Strong alkali Weak alkali acid 39. Anhydrous salt : A salt which does not contain any water of crystallisation is called anhydrous salt. For example, NaCl, NaNO3, Pb(NO3)2 40. Hydrated salt : A salt which contains definite number of molecules of water attached loosely to its one molecule is called hydrated salt. Examples : (i) CuSO4.5H2O (ii) Na2CO3.10H2O 41. Water of crystallisation : The number of water molecules which are loosely attached to one molecule of salt is called water of crystallisation. 42. Deliquescent substances : The water soluble substances which absorb moisture from the air and then dissolve in it, so as to form a liquid are called deliquescent substances, whereas the phenomenon is called deliquescence. Examples : (i) Anhydrous CaCl2 (ii) Anhydrous FeCl3. 6 Key Points 43. Hygroscopic substances : The substances which absorb moisture from the air but do not change their state are called hygroscopic substances. Examples : (1) Quicklime (2) conc. sulphuric acid. 44. Efflorescent substances : The hydrated crystalline salts which partly or wholly lose their water of crystallisation on exposure to air are called efflorescent substances and phenomenon is called efflorescence. Examples : (1) Na2CO3.10H2O (2) CuSO4.5H2O. 45. Amphoteric nature of some metals or their oxides : When metals such as aluminium or zinc or their oxides, reacts with acids as well as alkalis to form salt and water or hydrogen as the products, the metals or their oxides are said to be amphoteric in nature. 7 Key Points

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