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 Ostwald’s dilution law : Degree of dissociation of weak electrolyte,, =,  Ionic Product of water (Kw) = [H3O+] [OH–] = 10–14 at 298K, Le-Chatelier’s Principle : When a system of equilibrium is subjected to, a change in temperature, pressure or concentration, the equilibrium shifts, itself in such a way so as to undo or counterout the effect of change.,  Outcomes of Le-Chatelier’s Principle, Change at equilibrium, , Shift in equilibrium, , Increase in temperature, , Endothermic direction, , Decrease in temperature, , Exothermic direction, , Increase in pressure, , Towards lesser gaseous moles, , Decrease in pressure, , Towards greater gaseous moles, , Increase in Conc. of reactants, , Forward direction, , Increase in Conc. of products, , Reverse direction, ,  Conjugate Acid or Base :, Species — H+ = Conjugate base, Species + H+ = Conjugate acid,  pH of solution :, pH = —log [H3O+] or [H+] = 10–pH, pH + pOH = pKw = 14 at 298K,  Common ion effect : The depression of ionisation of weak electrolyte by, the presence of common ion from a strong electrolyte is called common, ion effect. For example degree of dissociation of NH4OH decreases in the, presence of strong electrolyte NH4CI.,  Hydrolysis of salts and pH of their solutions : Hydrolysis of salt is, de®ned as the reaction of cation or anion with water as a result of which, the pH of water changes., 1. Salts of strong and strong bases (e.g., NaCI) do not hydrolyse. The, solution pH will be 7., 2. Salts of weak acids and strong bases (e.g., CH3COONa) hydrolyse,, pH >7 (The anion acts as a base)., X–, 70, , +, , H2O, , Chemistry Class XI, , HX, , +, , OH–

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(Weak acid), (pKa + log C), , pH =, 3., , (Strong base), , Salt of strong acids and weak bases (e.g., NH4Cl) hydrolyse, pH < 7., (The cation acts as an acid)., M+ + H2O, pH =, , MOH + H+, (pKa + logC), , 4. Salt of weak acids and weak base (e.g., CH3COONH4) hydrolyse., The cation acts as an acid and anion as a base but whether the solution, is aodic or basic depends upon the relative values of Ka and Kb for these, ions., M+ + X + H2O, pH =, , MOH + HX, , (pKa – pKb), ,  Buffer solutions : The solutions, which resist the change in pH on dilution, or addition of small amounts of acid or base, are called buffer solutions.,  Basic buffer : Solution of weak base and its salt with strong acid, For, e.g., NH4OH + NH4CI,  Acidic buffer : Solution of weak acid and its salt with strong base, For, e.g., CH3COOH + CH3COONa.,  Henderson’s Equation for the pH of Buffer solution—, = pKa + log, , (for acidic buffer), , pOH = pKa + log, , (for basic buffer), , pH, ,  Solubility Product (Ksp) : The equilibrium constant that represent the, equilibrium between undissolved salt (solute) and its ions in a saturated, solution is called solubility product constant (Ksp)., For AxBy, Ksp, , xAy+ + yBx–, = [Ay+]x [Bx–]y, , If ionic product < Ksp ; salt remain dissolve., If ionic product > Ksp ; salt will be precipitated.,  Relationship between solubility (S) and solubility product (K sp)., Equilibrium, , 71

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Ksp, , = xx.yy.Sx + y, Ksp = S2, , For binary salts (e.g., AgCl, AgBr, Agl), , Ksp = 4S3, , For Ternary salts (e.g., Pbl2), , Chemical Equilibrium, 1-Mark Questions, 1. De®ne physical equilibrium. Give an example also., 2. Why is there a ®zz when soda water bottle is opened ?, 3. Justify the statement : ‘Both physical and chemical equilibria are dynamic, in nature’, 4. State Henry’s law., 5. In a reversible reaction, the two substances are in equilibrium. If the, concentration of each one is reduced to half, then what is the effect on the, equilibrium constant ?, 6. K1 and K2 are equilibrium constant for reactions (1) and (2), N2(g) + O2(g), , 2 NO(g), , NO(g), , 1/2 N2(g) + 1/2 O2(g), , then, calculate the relation between K1 and K2, 7. Write the equilibrium constant expression for the following reaction :, 3 Fe(s) + 4 H2O(g), , Fe3O4(s) + 4 H2(g), , 8. Classify the equilibrium as homogenous or heterogenous :, CH3COOC2H5(aq) + H2O(1), , CH3COOH(aq) + C2H5OH (aq), , (PNH ), , 9. Kp = (P ½ ) (PH3 )3/2, N2, 2, Write the balanced chemical equation corresponding to the above, expression., 10., , Give the direction in which the reaction would proceed if Qc > Kc, , 11. Hb(s) + O2(g), , HbO2(s), , Predict the direction in which equilibrium gets shifted if partial pressure, of O2(g) is lowered., 12. Discuss the position of equilibrium if the following reaction is carried out, in the presence of catalyst., 2SO2(g) + O2(g), 72, , 2SO3(g), , Chemistry Class XI

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13. In which case the yield of the product will be more., A, , B K1 = 1010, , X, , Y K2 = 106, , 14. Value of Kc at 500 K for A + 2B, , C is 10.6, , Determine the value of Kc at the same temperature for C, , A + 2B, , 15. Why do we sweat more on a humid day ?, 16. Why does a catalyst not affect the magnitude of equilibrium constant ?, 17. Write the relation between Kp and Kc for the given reaction., H2(g) + I 2(g), , 2HI(g), , 18. Write the expression of Kc for the following reaction, CH3COOC2H5(ac) + H2O(l), , CH3COOH(aq) + C2H5OH(aq), , 19. Write the expression of Kp for the following reaction, Cu(NO3)2 (s), , 2 CuO(s) + 4NO2(g) + O2(g), , 20. For an exothermic reaction, what happens to the equilibrium constant if, temperature is increase ?, 21. Ka for HA1 is 10 and Ka for HA2 is 12, Which acid is stronger., 22. For tribasic acid Ka1 > Ka2 > Ka3, What will happen to the acid strength of polyprotic acid if protons are, lost ?, 23. C(s), , C(s), , Diamond (Density = 3.5 g/cm3) Graphite (Density = 2.3 g/cm3), What will be the effect of increasing the pressure in this equilibrium., 24. Under what condition does the active mass becomes equal to the, molarity ?, 25. In which expression of Kc or Keq, that only solutions and gases are, involved ?, 26. What will be the change in the direction of equilibrium if Ne gas is added, in a reaction at constant volume., 27. What will be the effect on the boiling point of liquid if pressure is, increased ?, Equilibrium, , 73

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2-Mark Questions, 1. What is Kc for the following equilibrium when the equilibrium, concentration of each substance is :, [SO2] = 0.60M, [O2] = 0.82 M and [SO3] = 1.90 M ?, 2SO2(g) + O2(g), , 2SO3(g), , 2. At a certain temperature and total pressure of 105 Pa, iodine vapour contains, 40% by volume of I atoms, I2(g), , 2I(g), , Calculate Kp for the equilibrium., , [NCERT] [2.67 × 104 Pa], , 3. Explain why pure liquids and solids can be ignored while writing the, equilibrium constant expression ?, 4. A sample of HI(g) is placed in ¯ask at a pressure of 0.2 atm. At equilibrium, the partial pressure of HI(g) is 0.04 atm., What is Kp for the given equilibrium ?, 2 HI(g) H2 (g) + I2 (g), , [NCERT] [4], , 5. One mole of H2O and one mole of CO are taken in 10 L vessel and heated, to 725 K. At equilibrium 40% of water (by mass) reacts with CO according, to the equation,, H2O(g) + CO(g), , H2 (g) + CO2(g), , Calculate the equilibrium constant for the reaction., , [NCERT] [0.444], , 6. At 1127 K and 1 atm pressure, a gaseous mixture of CO and CO2 in, equilibrium with soild carbon has 90.55% CO by mass, C (s) + CO2(g), , 2CO(g), , Calculate Kc for this reaction at the above temperature.[NCERT] [0.153], 7. Describe the effect of :, (a) addition of H2, (b) addition of CH3OH, (c) removal of CO, (d) removal of CH3OH, on the equilibrium of the reaction :, 2H2(g) + CO (g), 74, , CH3OH(g), , Chemistry Class XI

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8. A + 3 B, , 2X K = x, , What will be the equilibrium constant for the decomposition of 1 mol, of x ?, 9. N2(g) + 3H2(g), N2(g) + O2(g), , 2 NH3(g), , K1, , 2 NO(g), , H2(g) + 1/2O2(g), , K2, , H2O(g), , K3, , Determine the equilibrium constant for, 2 NH3(g) + 5/2O2(g), 10. Kc for PCl5 (g), , 2NO(g) + 3H2O)(g), , PCl3 (g) + Cl (g) is 0.04 at 25°C, , How much mole of PCl5 must be added to 3 L ¯ask to obtain a chlorine, concentration of 0.15 M ?, [2.1], 3-Mark Questions, 1. Four moles of PCl5 are heated in a closed 4 dm3 container to reach, equilibrium at 400 K. At equilibrium 50% of PCl5 is dissociated. What is, the value of Kc for the dissociation of PCl5 into PCl3 and Cl2 at 400 K, [0.50], 2. (a) How does the value of equilibrium constant predict the extent of a, reaction ?, (b) Equilibrium constant for a reaction is 10. What will be the equilibrium, constant for the reverse reaction ?, 3. (a) De®ne the equilibrium constant., (b) For the general reaction :, a A(g) + b B(g), , c C (g) + d D(g), , Derive the relationship between Kp and Kc, 4. (a) What is meant by dynamic nature of equilibrium ?, (b) Consider the following transformation., A, , B, , K1 = 1, , B, , C, , K2 = 2, , C, , D, , K3 = 3, , Calculate the value of K for A, 5. Kc for SO2(g) + 1/2 O2(g), , D, SO3(g) at 600ºC is 61.7, Equilibrium, , 75

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Calculate Kp. What is the unit Kp for the above equilibrium. [R = 0.0821, L atm K–1 mol–1], 6. 3.2 mole of HI were heated in a sealed bulb at 444ºC till the equilibrium, state was reached. Its degree of dissociation was found to be 20%. Calculate, the number of moles hydrogen iodide, hydrogen and, iodine present at the equilibrium point and also determine the equilibrium, constant., 2HI(g), , H2 (g) + I2 (g), , 7. At 25ºC and 1 atm, the partial pressure in an equilibrium mixture of N 2O4, NO2 are 0.7 and 0.3 atm, respectively. Calculate the partial pressure when, they are in equilibriums at 25ºC and at a total pressure of 10 atm., 8. 13.8 g of N2O4 was placed in a 1L reaction vessel at 400 K and allowed, to attain equilibrium, N2O4 (g), 2NO2 (g), The total pressure at equilbrium was found to be 9.15 bar. Calculate Kc,, Kp and partial pressure at equilibrium., [Kc = 2.6], 9. The equilibrium constant for the following reaction is 1.6 × 105 at, 1024 K, H2(g) + Br(g), , 2HBr(g), , Find the equilibrium pressure of all gases if 10.0 bar a HBr is introduced, into a sealed container at 1024 K., [NCERT], –2, [PH2 eq. = PBr2 eq. = 2.5 × 10 bar; PHBr = 10.0 bar], 10. In a reaction :, CO(g) + 2H2(g), , CH3OH(l), , Hº = – 92 kj/mol, , Indicate the direction in which equilibrium will shift when, (i) Temperature is decreased., (ii) Pressure is decreased., (iii) Ne gas is added at constant pressure., 5–Mark Questions, 1. Dihydrogen gas is obtained from natural gas by partial oxidation with, steam as per following endothermic reaction :, CH4 (g) + H2O (g), , CO (g) + 3H2 (g), , (a) Write as expression for Kp for the above reaction., (b) How will the values of Kp and composition of equilibrium mixture, be affected by :, 76, , Chemistry Class XI

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(i) increasing the pressure, (ii) increasing the temperature, (iii) using a catalyst ?, 2. At 473 K, equilibrium constant Kc for decomposition of phosphorus, pentachloride, PCl5 is 8.3 × 10–3. If decomposition is depicted as,, PCl5(g), , PCl3(g) + Cl2(g), , Hº = 124.0 kJ mol–1, (a) Write an expression for Kc for the reaction., (b) What is the value of Kc for the reverse reaction at the same, temperature?, (c) What would be the effect on Kc if (i) more PCl5 is added (ii) pressure, is increased (iii) the temperature is increased ? [(b) KC = 120.48 (c), (i) No effect (ii) No effect (iii) Kc increase], 3. Ammonia is prepared by Haber’s process is which the following reaction, occurs, N2(g) + 3H2(g), , 2 NH3(g), , Hº = – 93.6 kJ, , Mention the effect of following on the equilibrium concentration of, ammonia., (a) Increasing pressure, (b) Increasing temperature, (c) Use of catalyst at an optimum temperature., (d) Addition of inert gas at constant volume., (e) Addition of inert gas at constant pressure., 4. Ethyl acetate is formed by the reaction between ethanol and acetic acid, and the equilibrium is represented as :, CH3COOC2H5(l) + H2O(l), CH3COOH(l) + C2H5OH(l), (i) Write the concentration ratio (reaction quotient), Qc, for this reaction, (note : water is not in excess and is not a solvent in this reaction), (ii) At 293 K, if one starts with 1.00 mol of acetic acid and 0.18 mol of, ethanol, there is 0.171 mol of ethyl acetate in the ®nal equilibrium, mixture. Calculate the equilibrium constant., (iii) Starting with 0.5 mol of ethanol and 1.0 mol of acetic acid and, maintaining it at 293 K, 0.214 mol of ethyl acetate is found after, sometime. Has equilibrium been reached ?, [(ii) 3.92 (iii) Qc = 0.204, Equilibrium has not been attained.], Equilibrium, , 77

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Ionic Equilibrium, 1–Mark Questions, 1. Which of the following are Lewis acids ?, H2O, BF3, H+, NH4+, 2. Write the conjugate acids for the following Bronsted bases., C6H5OH, H2O, 3. Write the conjugate bases for the following Bronsted acids., H2O, CH3COOH, 4. Which of the following are Lewis acids ?, (a) H2O, (b) AlCl3 (c) NH4+, 5. De®ne the Ostwald’s dilution law., 6. SO32– is Bronsted base or acid and why ?, 7. Why pH of our blood remains almost constant at 7.4 though we quite often, eat spicy food ?, 8. pH of black coffee is 5.0 at 25ºC. Is black coffee acidic or basic ?, 9. What will be the value of (pKa + pKb) at 25ºC., 10. What will be the pH of 1 M KNO3 solutions at 25ºC., 11. CaCl2(s) + sq, , CaCl2(aq) + Heat, , Discuss the solubility of CaCl2 if temperature is increased., 12. Why does the solubility of CO2 decrease with rise in temperature ?, 13. The solubility of A2 X3 is y mol dm–3. Calculate its solubility product., 14. Write the Ksp expression for Al (OH)3, 15. What is the condition for precipitation of a salt ?, 16. Pridict the nature of solution when NH4NO3 undergo hydrolysis., 17. Explain why pure NaCl precipitates out when HCl gas is passed through, the solution of NaCl ?, 18. Give the Henderson’s -Hasselbalch equation for an acidic buffer solution., 19. On which of the factors the equilibrium depend :, Temperature, nature of reactant and product, initial concentration and, pressure of the reactants., 78, , Chemistry Class XI

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20. What are amphoteric substances ? Give one example., 21. What could be the temperature 15ºC or 100ºC for Kw = 7.5 × 10–14., 22. What happens to ionic product of water if some acid is added to it ?, 23. What is the conjugate base of [Fe(H 2O)6]3+, 2–Mark Questions, 1. Explain ionic product of water. What is the effect of temperature on ionic, product of water ?, 2. What is pOH ? What is its value for neutral water at 25ºC, 3. (a) De®ne buffer solution, (b) Give one example each of acidic and basic buffer, 4. The solubility of Ca3(PO4)2 in water is x moles / litre. Calculate its, solubility product., [108x5], 5. Calculate the pH of a 0.01 M solution of acetic acid. Ka for CH3COOH, [3.37], is 1.8 × 10–5 at 25ºC., 6. Calculate pH when 9.8 g H2SO4 is dissolved in 2 litre of solution, 7. Calculate the pH of 10–9 M HCl., , [1], , [pH = 6.9957], , 8. An acid having pH = 6 is diluted 100 times. What will be the pH of the, ®nal solution ?, [pH = 6.98], 9. Calculate the pH of 10–10 M NaOH solution., , [pH = 7.0004], , 10. Solid Ba(NO3)2 is gradually dissolved in a 1.0 × 10–4 M Na2 CO3, solution. At what concentration of Ba2+ will a precipitate begin to, fotm ? (Ksp for BaCO3 = 5.1 × 10–9), [5.1 × 10–5 M], 11. The pKa of acetic acid and pKb of ammonium hydroxide are 4.76 and, 4.75 respectively. Calculate the pH of ammonium acetate solution., [7.005], 3–Mark Questions, 1. What is meant by the conjugate acid-base pair ? Find the conjugate acid/, base for the following species :, HNO2, CN–, HClO4, F–, OH–, OH3–, and S2–, 2. De®ne solubility product. Calculate the solubility product of Ca(OH)2 if, its solubility is 3., [Ksp = 108], Equilibrium, , 79

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3. Calculate the pH of the following mixture., 200 ml of M/10 H2SO4 + 400 ml of M/10 H3PO4 + 400 ml of M/10, HCl, [0.69], 4. The solubility product of AgCl in water is 1.5 × 10–10. Calculate its, solubility in 0.01 M NaCl aqueous solution., [1.5 × 10–8 M], 5. Predict whether a precipitate will be formed or not on mixing 20 ml of, 0.001 M NaCl solution with 80 ml of 0.01 M AgNO3 solution, Ksp for, [Yes, ppt. will be formed], AgCl is 1.5 × 10–10 ., 6. Equal volumes of three acids solution with pH 3, 4 and 5 are mixed in a, vessel.What will be the H+ ion concentration in the mixture ?, 7. Calculate the pH of a solution obtained by mixing 50 ml of 0.2 M HCl, and 50 ml of 0.1 M NaOH., [1.3010], 8. The pH of 0.1 M hydrocyanic acid solution is 5.2. What is the value of, Ka for hydrocyanic acid ?, [Ka = 3.69 × 10–10], 9. A buffer solution is prepared by mixing equal concentration of weak base, and its salt with strong acid. For the base Kb is given as 10–9. Calculagte, the pH of the buffer solution., [5], 10. Calculate the pH of the resultant mixtures :, (a) 10 mL of 0.2 M Ca(OH)2 + 25 mL of 0.1 M HCl, (b) 10 mL of 0.01 M H2SO4 + 10 mL of 0.01 M Ca(OH)2, (c) 10mL of 0.1 M H2SO4 + 10mL of 0.1 M KOH, [NCERT], [(a) 12.632 (b) 7 (c) 1.3], 11. Equal volumes of 0.002 M solutions of sodium iodate and cupric chlorate, are mixed together. Will it lead to precipitation of copper iodate ? (For, cupric iodate Ksp = 7.4 × 10–8)., [NCERT] [NO ppt. will ocurr], 12. What is the maximum concentration of equimolar solutions of ferrous, sulphate and sodium sulphide so that when mixed in equal volumes,, there is no precipitation of iron sulphide ? (For iron sulphide, Ksp = 6.3, [NCERT] [5.02 × 10–9 mol L–1], × 10–18), 13. The ionization constant of aniline is 3.69 × 10–10 :, (i) Calculate pH of 0.01 M solution of aniline., (ii) Calculate the degree of dissociation of aniline in the solution., (iii) Calculate the ionization constant of conjugate acid of the aniline., 80, , Chemistry Class XI

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14. The Ksp for Al(OH)3 is 2.7 × 10–11 . Calculate its solubility in g/L and, also pH of this solution., 15. Calculate the volume of water required to dissolve 0.3 gm of Zn(OH)2 to, get a saturated solution. Ksp [Zn(OH)2] = 1 × 10–15, [Atomic mass of Zn = 65.3, O = 16, H = 1], 16. The pH of an aqueous solution of ammonia is 11.5. Find the molarity of, the solution., Kb (NH4OH) = 1.8 × 10–5, , [0.57], , 17. What is the pH of the solution when 0.2 mole of HCl is added to 1 L of, the solution containing 0.1 M each of CH3COOH & acetate ion. Assume, that volume is 1 L., Ka (CH3COOH) = 1.8 × 10–5, , [1], 5–Mark Questions, , 1. Calculate the pH value of the following solutions., (a) 10–2 M HCl., (b) 10–3 M H2SO4., (c) 10–4 M NaOH, (d) 0.04 M NaOH., (e) 0.03 M HCl., , [(a) 2 (b) 2.6990 (c) 10 (d) 12.60 (e) 1.5229], , 2. (i) Calculate the pH of a buffer solution containing 2.0 mol/L CH3COOH, in 1.0 mol/L of CH3COONa . [Ka for CH3COOH is 1.8 × 10–5 at, 25ºC.], (ii) Calculate the change in pH of the buffer after the addition of 0.01 mol, NaOH., (iii) Calculate the pH of the buffer after the addition of 0.01 M HCl ?, [H. O. T.S], , [(i) 4.4337, (ii) 0.0065, (iii) 4,4372], , 3. (a) What is solubility product ? How is it different from ionic product ?, (b) Calculate the solubility of PbCl2 if its solubility product is 1.0 × 10–6, at 298 K., [6.3 × 10–3 M], 4. (a) Write short notes on :, (i) Common ion effect, (ii) Buffer capacity, Equilibrium, , 81

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(b) Calculate the pH of a buffer solution containing 0.2 mole of NH4Cl, and 0.1 mole of NH4OH per litre. Kb for NH4OH = 1.8 × 10–5, [8.966], 5. 500 ml saturated solution of Ca(OH)2 is mixed with equal volume of 0.4, M NaOH. How muchCa(OH)2 in mg is precipitated ?, [Ka (Ca(OH)2) = 4.42 × 10–5 at 25ºC], , [H.O.T.S], , 6. Calculate the pH of 0.1 M ammonia solution. Calculate the pH after 50, ml of this solution is treated with 25 ml of 0.1 M HCl., Kb (NH3) = 1.77 × 10–5 [11.12, 9.24], , 82, , Chemistry Class XI