What is the solubility of Cr(OH)₃ at a pH of 10.50? (Ksp Cr(OH)₃ is 6.70 × 10⁻³¹)

Answer 1

Cr(OH)₃(s) <==> Cr³⁺(aq) + 3OH^-(aq)

Ksp = 6.70x10^-31 = [Cr³⁺][OH^-]³

pH = 10.50

pOH = 14 - 10.50 = 3.50

[OH^-] = 1x10^-3.50 = 3.16x10^-4 M

6.70x10^-31 = [Cr³⁺][3.16x10^-4]³

[Cr³⁺] = 6.70x10^-31 / (3.16x10^-4)³

[Cr³⁺] = 2.12x10^-20 M = solubility of Cr(OH)₃ in pH 10.50