E-5 Solubility

Question 1

Write out a dissociation reaction for the following.

CuCl (s)

Answer 1

CuCl (s) ⇔ Cu⁺ (aq) + Cl^- (aq)

Question 2

Write out a dissociation equation for the following.

Ca(OH)₂ (s)

Answer 2

Cu(OH)₂ (s) ⇔ Ca²⁺ (aq) + 2 OH^- (aq)

Question 3

Write out a dissociation equation for the following.

Mn₃(PO₄)₂ (s)

Answer 3

Mn₃(PO₄)₂ (s) ⇔ 3 Mn²⁺ (aq) + 2 PO₄^3- (aq)

Question 4

Write out a K_sp expression for the following dissociation reaction.

CuCl (s) ⇔ Cu⁺ (aq) + Cl^- (aq)

Answer 4

K_sp = [Cu⁺][Cl^-]

Question 5

Write out a K_sp expression for the following dissociation reaction.

Cu(OH)₂ (s) ⇔ Ca²⁺ (aq) + 2 OH^- (aq)

Answer 5

K_sp = [Ca²⁺][OH^-]²

Question 6

Write out a K_sp expression for the following dissociation reaction.

Mn₃(PO₄)₂ (s) ⇔ 3 Mn²⁺ (aq) + 2 PO₄^3- (aq)

Answer 6

K_sp = [Mn²⁺]³[PO₄^3-]^₂

Question 7

Which of the following has a greatest molar solubility (no calculation)?

• Ca(OH)₂ K_sp = 5.02 x 10^-6
• Ba(BrO₃)₂ K_sp = 2.43 x 10^-4
• CdF₂ K_sp = 6.44 x 10^-3

Answer 7

CdF₂ - All form the same number of ions so I can compare the K_sp values. Largest is most soluble.

Question 8

Which of the following has a greatest molar solubility (no calculation)?

• CsClO₄ K_sp = 3.95 x 10^-3
• Ba(BrO₃)₂ K_sp = 2.43 x 10^-4
• Hg₂F₂ K_sp = 3.10 x 10^-6

Answer 8

All form a differnet number of ions so you can’t answer without a calculation.

Question 9

Which of the following has a lowest molar solubility (no calculation)?

• Ca(OH)₂ K_sp = 5.02 x 10^-6
• Ca(OH)₂ in 0.01 M NaOH K_sp = 5.02 x 10^-6
• Ca(OH)₂ in 0.001 M NaOH K_sp = 5.02 x 10^-6

Answer 9

Ca(OH)₂ in 0.01 M NaOH - OH^- from the NaOH acts as a common ion and forces the equilibrium to the left, lowering solubility. The 0.01 M solution is more concentrated so it has a greater impact.