The solubility-product constant for silver chromate in equilibrium with its constituent ions in water at 25°C is 1.1 × 10^{−12}\ M^3. Calculate the value of [Ag^+] that results when pure water is saturated with Ag_{2}CrO_{4}(s).
The Ag_{2}CrO_{4}(s) solubility equilibrium can be described by
Ag_{2}CrO_{4}(s) ⇋ 2\ Ag^+(aq) + CrO_{4}^{2−}(aq)and the corresponding solubility-product expression is
K_{sp} = [Ag^+]^2[CrO_{4}^{2−}] = 1.1 × 10^{−12}\ M^3Each Ag_{2}CrO_{4}(s) formula unit that dissolves yields two Ag^+(aq) ions and one CrO_{4}^{2−}(aq) ion; thus, [Ag^+] = 2s and [CrO_{4}^{2−}] = s. Substitution of this result into the K_{sp} expression for Ag_{2}CrO_{4}(s) yields
K_{sp} = (2s)^2(s) = 1.1 × 10^{−12}\ M^3Solving for s yields
s= 6.5 × 10^{−5}\ MThe value of [Ag^+] is
[Ag^+] = 2s = 1.3 × 10^{−4}\ M