PHYSICAL CHEMISTRY by: SHAILENDRA KR Classes at: - SCIENCE TUTORIALS; Opp Khuda Baksh Library, Ashok Rajpath, Patna PIN POINT STUDY CIRCLE; House No 5A/65, Opp Mahual Kothi, Alpana Market, Patna Topic: Ionic Equilibrium Meq Approach 01 02 M solution of monobasic acid is dissociated to 095% Calculate its dissociation constant Ans: 18 10 5 02 Calculate concentration of H + and degree of dissociation of 02 M acetic acid solution having K a = 18 10 5 Ans: 00095 or 095 % 03 K a for HA is 49 10 8 After making the necessary approximation Calculate for its decimolar solution (a) % dissociation (b) OH concentration (c) ph Ans: 143 10 10 04 Nicotinic acid (K a = 14 10 5 ) is represented by the formula HNiC Calculate its percent dissociation in a solution which contains 010 moles of nicotinic acid per 20 litre of solution Ans: 167 10 2 or 167 % 05 A solution of 001 M concentration of NH4OH is 26% dissociated Calculate [H + ], [OH ], [NH 4+ ], [NH 4 OH] and ph of solution Ans: 104145 06 Calculate the concentration of fluoroacetic acid which is required to get [H + ] = 150 10 3 M K a of acid = 26 10 3 Ans: 237 10 3 M 07 Determine degree of dissociation of 005 M NH 3 at 25ºC in a solution of ph = 11 Ans: 2 10 2 or 2% 08 Calculate ph of (i) 10 3 N HNO 3, (ii) 10 3 M H 2, (iii) 10 3 N H 2, (iv) 001 N HCl, (v) 10 8 N HCl, (vi) 10 2 M HCl Ans: (i) ph = 3, (ii) ph = 26989, (iii) ph =3, (iv) ph = 2, (v) ph = 69586 or ph = 69788,(vi) ph= 2 09 Calculate ph for acid solutions having [H + ] as (a) [H + ] = 005 M (b) [H + ] = 50 M (c) [H + ] = 10 8 M Ans: (a) ph = 13010 (b) ph = 2 (c) ph = 69586 10 Calculate ph for (a) 0001 N NaOH (b) 001 N Ca(OH) 2 (c) 001 M Ca(OH) 2 (d) 10 8 M NaOH (e) 10 2 M NaOH (f) 00008 M Mg(OH) 2 Page No: 1
Ans: (a) ph = 11 (b) ph = 12 (c) ph = 14 16989 = 123010 (d) ph = 69586 (e) ph = 2 (f) ph = 126989 11 Calculate ph of (a) 0002 N acetic acid having 23% dissociation (b) 0002 N NH 4 OH having 23% dissociaton Ans: (a) ph = 43372 (b) ph = 96627 12 Calculate ph of 010 N acetic acid having K a = 18 10 5 Ans: ph = 28726 13 What is [H + ] for a solution in which (i) ph = 3 (ii) ph = 475? Ans: (i) [H + ] = 10 3 M (ii) [H + ] = 17782 10 5 M 14 The ph of 01 M solution of weak monoprotic acid is 40 Calculate its [H + ] and K a Ans: [H + ] = 10 4 M, K a = Cα 2 = 10 4 10 3 = 10 7 15 The ph of 005 M aqueous solution of diethyl amine is 120 Calculate K b 16 The K w for 2H 2 O H 3 O + + OH change from 10 14 at 25ºC to 962 10 14 at 60ºC What is ph of water at 60ºC? What happen to its neutrality? Ans : Do Yourself 17 A solution of HCl has a ph = 5 If one ml of it is diluted to 1 litre, what will be ph of resulting solution? Ans: ph = 69788 18 Two gm of NaOH are dissolved in water to make 1 litre solution What is ph of solution? Ans: ph = 126989 19 Calculate the [Cl ], [Na + ], [H + ], [OH] and ph of resulting solution obtained by mixing 50 ml of 06 N HCl and 50 ml pf 03 N NaOH Ans: [Cl ] = 03 M, [Na + ] = 015 M, [H + ] = 015 M, [OH ] = 66 10 14 M, ph = 08239 20 Calculate the ph of solution obtained by mixing 10 ml of 01 M Hcl and 40 ml of 02 M H 2 Ans: ph = 04685 21 Calculate the ph of a solution which contains 100 ml of 01 M Hcl and 99 ml of 10 M NaOH Ans: ph = 30409 22 Calculate the ph of a solution which contains 99 ml of 1 M Hcl and 100 ml of 01 M NaOH Ans: ph = 109591 23 A solution contains 01 M H 2 S and 03 M HCl Calculate the conc of S 2 and HS ions in solution Given K a for H 2 S are 10 7 and 13 10 13 respectively 24 Calculate the change in ph of 1 litre buffer solution containing 01 mole each of NH 3 amd NH 4 Cl up on addition of, (i) 002 mole of dissolved gaseous HCl (ii) 002 mole of dissolved NaOH Assume no change in volume K NH3 = 18 10 5 Page No: 2
25 20 ml of 02 M NAOH are added to 50 ml of 02 M acetic acid (K a = 18 10 5 ) (i) What is ph of solution? (ii) Calculate volume of 02 M NaOH required to make the ph of solution 474 Ans: (i) ph = 45686 (ii) V = 25 ml 26 What volume of 01 M sodium formate solution should be added to 50 ml of 005 M formic acid to product a buffer solution of ph = 40; pk a of formic acid = 380 Ans: V = 3962 ml 27 Calculate the ratio of ph of a solution containing 1 mole of CH 3 COONa + 1 mole of HCl per litre and fo other solution containing 1 mole CH 3 COONa + 1 mole of acetic acid per litre 28 Calculate the composition of an acidic buffer solution made up of HA and NaA of total molarity 029 having ph = 44 and K a = 18 10 5 Ans: [Salt] = 009 M, [Acid] = 020 M 30 A certain buffer solution contains equal concentration of X and HX K b for X is 10 10 Calculate ph of buffer Ans: ph = 4 31 01 M CH 3 COOH solution is titrated against 005 M NaOH solution Calculate ph at 1/4th and 3/ 4th stages of neutralization of acid The ph for 01 M CH 3 COOH is 3 32 K SP of AgCl is 28 10 10 at 25ºC Calculate solubility of AgCl in; (a) Pure water (b) 01 N AgNO 3 (c) 01 M KCl or 01 M NaCl Ans: (a) 1673 10 5 mole litre 1 (b) 28 10 9 mole litre 1 (c) 28 10 9 mole litre 1 33 The solubility product of SrF 2 in water is 8 10 10 Calculate its solubility is 01 M NaF aqueous solution Ans: 8 10 8 M 34 The solubility of AgCl in water at 25ºC is 179 10 3 g/litre Calculate K SP of AgCl at 25ºC Ans: 155 10 10 mole litre 1 35 K SP of AgBr is 4 10 13 and [Ag + ] in a solution is 1 10 6 mole litre 1 What is the [Br ] in that solution? Ans: 4 10 7 mole litre 1 36 The [Ag + ] ion in a saturated solution of Ag 2 CrO 4 at 25ºC is 15 10 4 M Determine K SP of Ag 2 CrO 4 at 25ºC Ans: 1688 10 12 mole litre 3 37 Equal volumes of 002 M CaCl 2 and 00004 M Na 2 are mixed Will a precipitate form? 38 An acid type indicator, HIn differs in colour from its conjugate base (In ) The human eye is sensitive to colour differences only when the ratio [In ] / [HIn] is greater than 10 or smaller than 01 What should be the minimum change in the ph of the solution to observe a complete colour change (K a = 10 10 5 )? Page No: 3
39 Calculate ph at which Mg(OH) 2 begins to precipitate from a solution containing 010 M Mg +2 ions K SP = 1 10 11 Ans: ph = 9 40 Calculate ph of a saturated solution K SP for Mg(OH) 2 is 89 10 12 Ans: ph = 104168 41 Will a precipitate be formed in a 0001 M solution of Mg(NO 3 ) 2, if the ph solution is adjusted to 9? K SP = 89 10 12 42 Zn salt is mixed with (NH 4 ) 2 S of molarity 0021 M What amount of Zn +2 will remain unprecipitated in 12 ml of the solution? K SP of ZnS = 451 10 24 Ans: 1677 10 22 g/12 ml 43 A solution has 005 M Mg +2 and 005 M NH 3 Calculate the concentration of NH 4 Cl required to prevent the formation in solution K SP = 90 10 12 and ionisation constant of NH 3 is 18 10 5 Ans: 0067 M 44 Calculate the solubility of AgCN in a buffer solution of ph = 3 Given K SP of AgCN = 12 10 16 and K a for HCN = 48 10 10 Ans: 158 10 5 mole litre 1 45 Calculate the hydrolysis constant of the salt containing NO - ions Given K for HNO = 45 2 a 2 10 10 Ans: 22 10 5 46 What is the ph of a 05 M aqueous NaCN solution? pk b of CN = 470 Ans: 115 47 Calculate the pecentage hydrolysis in 0003 M aqueous solution of NaOCN K a for HOCN = 333 10 4 Ans: 10 2 48 Calculate degree of hydrolysis and ph of 02 M solution of NH 4 Cl Given K b for NH 4 OH is 18 10 5 Ans: 49771 49 Find out the amount of NH 4 Cl dissolved in 500 ml to have ph = 45 K b for NH 4 Cl is 18 10 5 Ans: 4815 g 50 Calculate for 001 N solution of sodium acetate, (a) Hydrolysis constant (b) Degree of hydrolysis (c) ph Given K a = 19 10 5 Ans: (a) 526 10 10 (b) 229 10 4 (c) ph = 836 51 K a for butyric acid is 20 10 5 Calculate ph and hydroxyl ion concentration in 02 M aqueous solution of sodium butyrate 52 K a for ascorbic acid (HAsc) is 5 10 5 Calculate the hydrogen ion concentration and percentage of hydrolysis in an aqueous solution in which the concentration of Asc ions is 002 M Ans: 10 4 Page No: 4
53 Calculate the ph at the equivalence point when a solution of 01 M acetic acid is titrated with a solution of 01 M NaOH K a for acid = 19 10 5 Ans: 871 54 Calcium lactate is a salt of weak acid and represented as Ca(LaC) 2 A satirated solution of Ca(LaC) 2 contains 013 mole of salt in 050 litre solution The poh of this is 560 Assuming complete dissociation of salt, calculate K a of lactic acid Ans: K a = 825 10 4 55 Calculate ph of the follwing mixture Given that Pk a = 47, Pk b = 474 (a) 50 ml of 010 M NaOH + 50 ml 005 M CH 3 (b) 50 ml of 005 M NaOH + 50 ml 010 M CH 3 (c) 50 ml of 010 M NaOH + 50 ml 010 M CH 3 (d) 50 ml of 010 M NH 4 OH + 50 ml 005 M HCl (e) 50 ml of 005 M NH 4 OH + 50 ml 010 M HCl (f) 50 ml of 010 M NH 4 OH + 50 ml 010 M HCl (g) 50 ml of 005 M NH 4 OH + 50 ml 005 M CH 3 Ans: (a) 123979 (b) 47447 (c) 87218 (d)92553 (e) 16021 (f) 52782 (g) 7 56 Calculate the ph at the equivalence point when 40 ml of 01 M CH 3 COOH is neutralized by 02 M NaOH Given K a for CH 3 COOH = 10 5 Ans: 89122 57 Equilibrium constant for the acid ionisation of Fe +3 to Fe(OH) +2 and H + is 65 10 3 What is the maximum ph which could be used so that at leat 95% of the total Fe +3 in a dilute solution exists as Fe +3 Ans: 09083 58 Calculate ph of 0001 M solution of ZnCl 2 Kb for Zn(OH) 2 = 22 10 12 Ans: 63486 59 Calculate the ph of 01 M K 3 PO 4 solution The third dissociation constant of orthophosphoric acid is 13 10 12 Assume that the hydrolysis proceeds only in the first step Ans: 124366 60 The ionisation constant of NH + in water is 56 4 10 10 at 25ºC The rate constant for the reaction of NH + and 4 OH to form NH 3 and H 2 O at 25ºC is 34 10 10 litre mole 1 sec 1 Calculate the rate constant for proton transfer from water to NH 3 Ans: 607 10 5 Page No: 5