Solubility of Cr hydroxide in buffered solution

[tiggrulz13]

Homework Statement

What is the solubility (gram/liter) of Cr(OH)3 (103.02 g/mol) in a solution buffered at pH = 8.673? The pKsp of Cr(OH)3 is 30.220.

Homework Equations

Ksp = [Cr][OH]^3
Cr(OH)3 -> Cr + 3OH

The Attempt at a Solution

I have already solved that Ksp = 6.0256 E -31, but I'm not entirely sure what to do with the buffer pH. I tried using it to find the pOH and subsequently [OH], but for some reason I'm not getting the right answer. Do I plug [OH] into the Ksp equation after finding out the concentration using the pH or is there a step I'm missing?

 

[chemisttree]

Sounds like you are approaching it correctly. Use the concentration of [OH-] you obtain from the pOH in the Ksp expression and determine [Cr+3]. From that revelation back out how many grams of Cr(OH)3 will produce that concentration of [Cr+3].