Question

What is the solubility of CaF₂ in g/L if Ksp = 4.0 x 10⁻8?

a) Calculated solubility = 4 x 10⁻4 g/L
b) Calculated solubility = 2 x 10⁻4 g/L
c) Calculated solubility = 8 x 10⁻4 g/L
d) Calculated solubility = 3 x 10⁻4 g/L

Answer 1

The correct answer for the solubility of CaF₂ in g/L, given a Ksp of 4.0 x 10⁻⁸, is (b) 2 x 10⁻⁴ g/L.

Step-by-step explanation:

The solubility of CaF₂ in g/L can be determined using its Ksp value. The dissolution of CaF₂ can be shown as: CaF₂ (s) ⟶ Ca²⁺ (aq) + 2F⁻(aq). From the Ksp expression for CaF₂, which is Ksp = (s)(2s)² = 4s³, we can solve for s (molar solubility) and then convert it to g/L using CaF₂'s molar mass.

Firstly, we solve the equation 4s³ = 4.0 x 10⁻⁸ for s, yielding s ≈ 1 x 10⁻⁹ Molar. To get the solubility in g/L, multiply the molarity by the molar mass of CaF₂, which is 78.1 g/mol:

Solubility (g/L) = 1 x 10⁻⁹ (Molar) x 78.1 (g/mol)

This gives us a solubility of CaF₂ approximately equal to 2 x 10⁻⁴ g/L. Therefore, the correct answer is (b) Calculated solubility = 2 x 10⁻⁴ g/L.