Calculate the solubility of Co(OH) 3 Ksp=2.2×10^16 in a buffered solution with a pH=11.0

Question

Calculate the solubility of Co(OH) 3 Ksp=2.2×10^16 in a buffered solution with a pH=11.0

Answer 1

Co(OH)₃ <==> Co³⁺ + 3OH^-

Ksp = [Co₃₊][OH^-]³ = 2.2x10^-16 (not 2.2x10¹⁶)

pH = 11 thus pOH = 14-11 = 3

[OH^-] = 1x10^-3

Ksp = 2.2x10^-16 = [Co³⁺][OH^-]³ = (x)(1x10^-3)³

2.2x10^-16 = 1x10^-9x

x = 2.2x10^-7 M = solubility of Co(OH)₃ under these conditions.