Jika diketahui Ksp Fe(OH)2 sebesar 8 × 10 min 15 kelarutan Fe(OH)2 sebesar

Fe(OH)2 --> Fe2+ + 2OH-
                      s           2s

Maka,
Ksp Fe(OH)2 = [Fe2+][OH-]^2
8 x 10^-15 = (s)(2s)^2
s^3 = 2 x 10^-15
s = 13 x 10^-6 mol/L