Solubility from K<sub>sp</sub> for a 1:2 salt
CaF2 has Ksp = 4.0 × 10⁻¹¹. What is its molar solubility?
Answer C: explanation for every choice
A
This is the Ksp itself, not the solubility.
B
This takes √Ksp, which applies only to 1:1 salts.
C
Correct. Ksp = [Ca²⁺][F⁻]² = s(2s)² = 4s³, so s³ = 1.0 × 10⁻¹¹ and s ≈ 2.2 × 10⁻⁴ M.
D
This takes the cube root of Ksp without dividing by 4 first.
TakeawayWrite Ksp in terms of s using the formula's stoichiometry. For MX₂, Ksp = 4s³.
Equation usedSolubility product
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