1. Write the Dissolution Equilibrium:
CaF₂(s) ⇌ Ca²⁺(aq) + 2F⁻(aq)
2. Set up the Ksp Expression:
Ksp = [Ca²⁺][F⁻]²
3. Define Solubility (s):
* Let 's' represent the molar solubility of CaF₂.
* This means that 's' moles of CaF₂ dissolve per liter of solution, producing 's' moles of Ca²⁺ and 2's' moles of F⁻.
4. Substitute 's' into the Ksp Expression:
Ksp = (s)(2s)² = 4s³
5. Solve for 's':
* Ksp = 3.9 x 10⁻¹¹ = 4s³
* s³ = (3.9 x 10⁻¹¹)/4
* s = ³√((3.9 x 10⁻¹¹)/4)
* s ≈ 2.1 x 10⁻⁴ M
Therefore, the solubility of CaF₂ at 25°C is approximately 2.1 x 10⁻⁴ M.
