CHM 2046C Sample Module 12 Name: __Answers_____

H. Comparing Solubility of Salts 10 points

An insoluble substance is defined as one that has solubility less than 0.01 moles/liter of water.

Using K_sp values, tell which salt in each pair is more soluble in water:

1. AgCl (K_sp = 1.8 x 10^-10) or AgCN (K_sp = 6.0 x 10^-17)

Answer: AgCl

2. Mg(OH)₂ (K_sp = 5.6 x 10^-12) or Ca(OH)₂ (K_sp = 5.5 x 10^-5)

Answer: Ca(OH)₂

3. MgCO₃ (K_sp = 6.8 x 10^-6) or CaCO₃ (K_sp = 3.4 x 10^-9)

Answer: MgCO₃

4. FeCO₃ (K_sp = 3.1 x 10^-11) or Ag₂C₂O₄ (K_sp = 5.4 x 10^-12)

Answer: Ag₂C₂O₄

Which compound in each pair is more soluble in water than is predicted by a calculation from K_sp :

5. AgBr (K_sp = 5.4 x 10^-13) or AgCN (K_sp = 6.0 x 10^-17)

Answer: AgCN because the CN is the conjugate base of the weak acid HCN

6. PbCl₂ (K_sp = 1.7 x 10^-5) or PbCO₃ (K_sp = 7.4 x 10^-14)

Answer: PbCO₃

7. PbCl₂ (K_sp = 1.7 x 10^-5) or PbF₂ (K_sp = 3.3 x 10^-8)

Answer: PbF₂

Which insoluble compound in each pair should be more soluble in nitric acid than in pure water:

8. PbCl₂ (K_sp = 1.7 x 10^-5) or PbS (K_sp = 9.0 x 10^-24)

Answer: PbS Nitric Acid’s Hydrogen ions react with the sulfide ion in solution, this shifting the equilibrium to the right to replenish the dissolved Sulfide ions.

9. AgCl (K_sp = 1.8 x 10^-10) or Al(OH)₃ (K_sp = not known)

Answer: Al(OH)₃ Nitric Acid’s Hydrogen ions neutralize the OH^1- ions in solution, causing the Equilibrium to shift to the right. Thus Aluminum hydroxide has greater solubility in nitric acid than Lead II Chloride.

10. AgI (K_sp = 8.5 x 10^-17) or Ag₂CO₃ (K_sp = 8.5 x 10^-12)

Answer: Ag₂CO₃

Addition worked examples:

McMurry Reference:

See Problem 15.23 on page 621. Note the Key Concept Problem 15.24 on page 622.

Try the end of chapter problems: 15.102 and 15.103 on page 642.

Kotz Reference:

See Section 18.4 pages 878-879. Work exercise 18.14 p 879.

Work questions 52, 57 and 58 on page 897 at the end of chapter 18.