Question

Consider the addition of MgF2 and CaF2 in water as given in (a) and (b)

(a) 4.96mg of MgF2 in 125 mL of pure water Ksp of MgF2 = 3.2 × 10-8 (b) 3.9mg of CaF2 in 100 mL of pure water, Ksp of CaF2 = 4 × 10-12. Choose the correct statement(s) from amongst the following.

• A. MgF2 will completely dissolve
• B. MgF2 solution will have 32% saturation.
• C. CaF2 will not completely dissolve
• D. CaF2 solution will have 100% saturation.

Answer 1

Answer: (C)

CaF2 will not completely dissolve

Answer 2

For MgF2, the initial concentration (6.37 × 10⁻⁴ M) is less than its solubility (2 × 10⁻³ M), so it dissolves completely, and the solution is unsaturated (approx. 32% saturated).

For CaF2, the initial concentration (4.99 × 10⁻⁴ M) is greater than its solubility (1 × 10⁻⁴ M), so it will not dissolve completely, and the solution will be saturated (100% saturated).