What is the Kb value for the formation of iron (III) hydroxide?

Question

The reaction I have in mind is:

Fe3+ + OH- <--> Fe(OH)3

Thanks.

Answer 1

Fe(OH)3 is VERY insoluble in water. The only equilibrium constant that applies is the solubility product constant, Ksp:

Ksp = [Fe+++] [-OH]³ = 4x10^-38 (see source below).

This corresponds to a molar solubility of about 2x10^-10 M. Even at saturation, the pH wouldn&#039;t hardly budge from 7. Of course, adding acid will solubilize the Fe+++ ions.