Copper(II) arsenate has a Ksp of 7.6×10⁻³⁶.Determine the molar solubility of copper(II) arsenate in a solution of 0.10 mol/L sodium arsenate.

Question

The dissolution of solid copper(II) arsenate in aqueous solution at equilibrium is: Cu₃(AsO₄)₂(s) ⇌ 3 Cu²⁺(aq) + 2 AsO₄³⁻(aq).

The molar solubility of copper(II) arsenate in pure water is 3.7x10⁻⁸

Answer 1

This is a problem involving the common ion effect. The common ion in this case is arsenate.

Cu₃(AsO₄)₂(s) <==> 3Cu²⁺(aq) + 2AsO₄^3-(aq)

Ksp = [Cu²⁺]³[AsO₄^3-]²

3.7x10^-8 = (x)³(0.1)

x³ = 3.7x10^-7

x = 7.2x10^-3 M = [Cu²⁺]

Molar solubility of Cu₃(AsO₄)₂ = 7.2x10^-3 M Cu²⁺ x 1 Cu₃(AsO₄)₂ / 3 Cu²⁺ = 2.4x10^-3 M