A chemist wishes to prepare a standard aqueous solution that as a concentration of Fe3+ equal to 1.0x10^-5 M. This solution is to be prepared by allowing water at a set pH to reach equilibrium with solid Fe(OH)3. What pH should be used for the aqueous solution to give this desired concentration of [Fe3+]?

I just wanted to make sure I'm doing this right.

eFirst I set up my equation as:

\(Fe(OH)_3 -> Fe^{3+} + 3OH^-\)

So I know that the Ksp equation is:
\([OH^-]^3[Fe^{3+}]=2.0x10^-39\)

\([OH^-]^3=\frac{2.0x10^-39}{1.0x10^-5}\)

And I calculated a concetration of 5.8x10^-12. I then took the negative logarithm of this to get the pOH value and subtract that from 14 to get my final pH value of 2.8. Is this right?