What is Kc for this equilibrium?

Question

Solid Ca₃(PO₄)₂ is placed into 10.0 L of water. When equilibrium is established, the concentration of Ca²⁺ is 2.3 × 10⁻⁴ M. What is Kc for this equilibrium? Note Kc is sometimes called K.

Ca₃(PO₄)₂ (s) ⇌ 3 Ca²⁺ (aq) + 2 PO₄³⁻ (aq)

Answer 1

K_SP = [Ca²⁺]³[PO₄^3-]² If you let x be the concentration of Ca²⁺, then the PO₄^3- concentration by stoichiometry is 2/3 x

K_SP = x³(2x/3)² = x⁵ (4/9) (plug in)