The molar solubility of calcium fluoride, CaF2, is 2.0 x 10^-4M. What is the concentration of fluoride ion in a saturated solution?

Answer is: concentration of the fluoride ion is 0.0368 M.

Chemical reaction: CaF ₂ (s) → Ca²⁺ (aq) + 2F⁻ (aq).

Ksp = 2.0·10⁻⁴ M.

Ksp = [Ca² ⁺] · [F⁻ ]².

[Ca²⁺] = x.

[F⁻] = 2[Ca²⁺] = 2x.

Ksp = x · (2x) ².

2.0·10⁻⁴ = 4x³.

x = [F⁻] = ∛ (2.0·10⁻⁴ : 4).

[F⁻] = 0.0368 M.