Practice Problems Acid-Base Equilibria and Solubility Equilibria

1. Write the solubility product constant expression for equilibrium in a saturated solution of (a) iron(III) hydroxide and (b) gold(III) oxalate.

Fe(OH)3(s) → ← Fe3+(aq) + 3 OH–(aq)

Au2(C2O4)3(s) → ← 2 Au3+(aq) + 3 C2O42–(aq)

2. When does pH affect the solubility of a slightly soluble solute, and when does it not? Give some examples.

3. Explain why PbCl2(s) is less soluble in 1 M Pb(NO3)2 than in pure water, but somewhat more soluble in 1 M HCl(aq) than in pure water.

4. Write an equation involving [Al(H2O)6]3+ to account for the fact that aqueous solutions of Al3+ are acidic.

5. Write a chemical equation representing solubility equilibrium for (a) Hg2(CN)2, Ksp = 5×10–40; and (b) Ag3AsO4, Ksp = 1.0 ×10–22.

6. Write a chemical equation representing solubility equilibrium for (a) YF3; Ksp = 6.6×10–13; and (b) Fe4[Fe(CN)6]3, Ksp = 3.3×10–41.

7. The Ksp values of CuCO3 and ZnCO3 are 1.4×10–10 and 1.4×10–11, respectively. Does this mean that CuCO3 has ten times the solubility of ZnCO3? Explain.

8. Calculate Ksp values of the following, for which a reference book lists the indicated solubilities: (a) Ce(IO3)4, solubility 1.8×10–4 mol/L; (b) Hg2SO4, 8.9×10–4 mol/L; and (c) barium chromate, 0.0010 g BaCrO4/100 mL H2O.

9. Calculate the concentration of Cu2+ in parts per billion (ppb) in a saturated solution of copper(II) arsenate, Cu3(AsO4)2(aq). (Hint: Recall that 1 ppb signifies 1 g Cu2+ per 109 g solution.)

10. A solution is saturated with Ag2SO4. (a) Calculate [Ag+] in this saturated solution. (b) What mass of Na2SO4 must be added to 0.500 L of the solution to decrease [Ag+] to 4.0×10–3 M.

11. What [CrO42–] must be present in 0.00105 M AgNO3(aq) to just cause Ag2CrO4(s) to precipitate?

12. In hard water, [Ca2+] is about 2.0×10–3 M. Water is fluoridated with 1.0 g F– per 1.0×103 L of water. Will CaF2(s) precipitate from hard water upon fluoridation?

13. Calculate the solubility of Mg(OH)2 in a buffer solution that is 0.75 M NH3 and 0.50 M NH4Cl.

14. Which of the following complex ions would you expect to have the lowest [Ag+] in a solution that is 0.10 M in the complex ion and 1.0 M in the free ligand? Explain.

(a) [Ag(NH3)2]+

(b) [Ag(CN)2]–

(c) [Ag(S2O3)2]3–

15. When a few drops of concentrated Na2SO4(aq) are added to a dilute solution of AgNO3(aq), a white precipitate forms. When a small quantity of concentrated NH3(aq) is added to the mixture, the precipitate redissolves, resulting in a colorless solution. When this solution is made acidic with HNO3(aq), a white precipitate again appears. Write equations to represent these three observations.

16. What is the [Zn2+] in a solution that is 0.25 M in [Zn(NH3)4]2+ and has [NH3] equal to 1.50 M?

Answers