Calculating Ksp for Iron(II) Hydroxide

[Qube]

Homework Statement

A saturated solution of iron(II) hydroxide has a molar solubility of 3.65 x 10^-6 M. Calculate the Ksp for Fe(OH)2.

Homework Equations

Ksp = [A]^a^b

The Attempt at a Solution

Fe(OH)2 --> Fe^2+ + 2OH-

Ksp = [3.65 x 10^-6 M] * (2*[3.65 x 10^-6 M])^2

This, however, doesn't yield an answer. The professor's answer is equivalent to

[3.65 x 10^-6 M] * ([3.65 x 10^-6 M])^2

I'm assuming this is an error on his part because the concentration of hydroxide ions should be twice the concentration of iron ions, not the same.

 

[Borek]

Your approach is the correct one.