1. 500 mL of 0.2 M aqueous solution of acetic acid is mixed with 500 mL of 0.2 M HCl at 25°C.
(i) Calculate the degree of dissociation of acetic acid in the resulting solution and pH of the solution. (ii) If 6 g of NaOH is added to the above solution, determine the final pH (assuming there is no change in volume on mixing, Ka of acetic acid is 1.75 × 10– 5 mol/L.
Ans. αααα = 1.75 × 10– 2%; pH = 1
2. The average concentration of SO2 in the atmosphere over a city on a certain day is 10 ppm, when the average temperature is 298 K. Given that the solubility of SO2 in water at 298 K is 1.3653 mol/L and pKa of H2SO3 is 1.92, estimate the pH of rain on that day.
Ans. 0.5
3. The solubility of Pb(OH)2 in water is 6.7 × 10– 6 M. Calculate the solubility of Pb(OH)2 in a buffer solution of pH = 8.
Ans. 1.2 × 10– 3 M
4. What will be the resultant pH when 200 mL of an aqueous solution of HCl (pH = 2.0) is mixed with 300 mL of an aqueous solution of NaOH (pH = 12.0)?
Ans. pH = 11.3
5. Given, Ag(NH )3 2+→Ag++2NH3,
Kc = 6.2 × 10– 8 and Ksp of AgCl = 1.8 × 10– 10 at 298 K. If ammonia is added to a water solution containing excess of AgCl(s) only. Calculate the concentration of the complex in 1.0 M aqueous ammonia.
Ans. [Ag(NH3)2]+ = 0.054 M
6. An acid type indicator, H/n differs in colour from its conjugate base (In–). The human eye is sensitive to colour differences only when the ratio [In–] / [H/n] is greater than 10 or smaller than 0.1. What should be the minimum change in the pH of the solution to observe a complete colour change? (Ka = 1.0 × 10– 5)
Ans. 4 to 6
7. A sample of AgCl was treated with 5.00 mL of 1.5 M Na2CO3 solution to give Ag2CO3. The remaining solution contained 0.0026 g of Cl– ions per litre. Calculate the solubility product of AgCl. [Ksp (Ag2CO3) = 8.2 × 10– 12]
Ans. 96 gm
Formatted: Space Before: 3 pt, After: 0 pt, Line spacing: Multiple 1.2 li
Formatted: Space Before: 3 pt, Line spacing: Multiple 1.2 li
Sri Chaitanya IIT-JEE Head Office: 11, Central Market, West Punjabi Bagh , New Delhi-110 026. Phones: 25226309/10. 8. What is the pH of a 0.50 M aqueous NaCN solution? pKb of CN– = 4.70
Ans. 11.5
9. Calculate the pH of an aqueous solution of 1.0, M ammonium formate assuming complete dissociation (pKa of formic acid = 3.8 and pKb of ammonia = 4.8)
Ans. 6.5
10. An aqueous solution of a metal bromide MBr2 (0.05 M) is saturated with H2S. What is the minimum pH which MS will precipitate.
Ksp for MS = 6.0 × 10– 21, conc. of saturated H2S = 0.1 M and K1 = 10– 7 and K2 = 1.3 × 10– 13, for H2S. Ans. 0.983
11. The pH of blood stream is maintained by a proper balance of H2CO3 and NaHCO3 concentrations. What volume of 5 M NaHCO3 solution should be mixed with a 10 mL maintain a pH of 7.4?
Ka for H2CO3 in blood is 7.8 × 10– 7 Ans. 78.36
12. The solubility product (Ksp) of Ca(OH)2 at 25°C is 4.52 × 10– 5. A 500 mL of saturated solution of Ca(OH)2 is mixed with equal volume of 0.4 M NaOH. How much Ca(OH)2 in milligrams is precipitated.
Ans. 7.58
13. A 40.0 mL solution of a weak base, BOH is titrated with 0.1 N HCl solution. The pH of the solution is found to be 10.04 and 9.14 after the addition of 5.0 mL and 20.0 mL of the acid respectively. Find out the dissociation constnat of the base.
Ans. 1.81 × 10– 5
14. The solubility product of Ag2C2O4 at 25°C is 1.29 × 10– 11 mol3 L– 3. A solution of K2C2O4 containing 0.1520 mole in 500 mL water is shaken at 25°C with excess of Ag2CO3 till the following equilibrium is reached:
Ag2CO3 + K2C2O4 → Ag2C2O4 + K2CO3
At equilibrium, the solution contains 0.0358 mole of K2CO3. Assuming the degree of dissociation of K2C2O4 and K2CO3 to be equal, calculate the solubility product of Ag2CO3.
Ans. 3.9 × 10– 12
15. What is the pH of a 1.0 M solution of acetic acid? To what volume must one litre of this solution be diluted so that the pH of the resulting solution will be twice the original value? Given : Ka = 1.8 × 10–5
16. Freshly precipitated aluminium and magnesium hydroxides are stirred vigorously in a buffer solution containing 0.25 mol/L of NH4Cl and 0.05 M of ammonium hydroxide. Calculate the concentration of aluminium and magnesium ions in solution.
Kb [NH4OH] = 1.8 × 10– 5 Ksp [Mg(OH)2] = 8.9 × 10– 12 Ksp [Al(OH)3] = 6 × 10– 32 Ans. [Al+ 3] = 1.28 × 10– 15; [Mg2 +] = 0.686
17. How many gram-mole of HCl will be required to prepare one litre of buffer solution (containing NaCN and HCl) of pH 8.5 using 0.01 gram formula weight of NaCN? KHCN = 4.1 × 10– 10 Ans. 8.85 × 10– 3
18. What is the pH of the solution when 0.20 moles of HCl is added to one litre of a solution containing (i) 1 M each of acetic acid and acetate ion
(ii) 0.1 M each of acetic acid and acetate ion
Assume the total volume is one litre. Ka for acetic acid = 1.8 × 10– 5. Ans. (i) 4.57; (ii) 1
19. The solubility of Mg(OH)2 in pure water is 9.57 × 10– 3 g/L. Calculate its solubility (in g/L) in 0.02 M Mg(NO3)2 solution.
Ans. 8.7 × 10– 4 gm/L
20. The concentration of hydrogen ions is a 0.2 molar solution of formic acid is 6.4 × 10– 3 mol/L. To this solution, sodium format is added so as to adjust the concentration of sodium formate to one mole per litre. What will be the pH of this solution? The dissociation constant of formic acid is 2.4 × 10– 4 and the degree of dissociation of sodium formate is 0.75.
Ans. pH = 4.2
21. A solution contains a mixture of Ag(0.10 M) and Hg2 + (0.10 M) which are to be separated by selective precipitation. Calculate the maximum concentration of iodine ion at which one of them gets precipitated almost completely. What percentage of that metal ion is precipitated? Ksp : AgI = 8.5 × 10– 17, HgI2 = 2.5 × 10– 26
Ans. [I–] = 5 × 10– 13 M
22. The dissociation constant of a weak acid HA is 4.9 × 10– 8. After making the necessary approximations, calculate
(i) percentage ionization (ii) pH
Sri Chaitanya IIT-JEE Head Office: 11, Central Market, West Punjabi Bagh , New Delhi-110 026. Phones: 25226309/10. (iii) OH– concentration in a decimolar solution of the acid. Water has a pH of 7.
Ans. (i) 0.07%; (ii) 4.15; (iii) 1.4 × 10– 10
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Exercise - I
True/False 1.1. True 2. True 3. False 4. False 5. False
Fill in the Blanks
1. 1. pKw 2. decrease 3. strong
4. neutralization 5. anionic
Assertion and Reason 1.
1. (a) 2. (a) 3. (d) 4. (b) 5. (c)