Question

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 1

Answer is: concentration of the fluoride ion is 0.0368 M.
Chemical reaction: CaF₂(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.