Homework Help: Chem

Posted by Kim on Tuesday, October 26, 2010 at 6:30pm.

The question is;
About Fe+2 concentration will Fe(OH)2 precipitate from a buffer solution that has a PH = 9.29? The Ksp of Fe(OH)2 is 4.87x10^-17

So here is what I did,
Ksp = (x) (2x)^2 = 4x^3
4.87x10^-17 = 4x^3
x = 2.30x10^-6

I dont know what do I have to do
after this.
Plz help me!

Chem - DrBob222, Tuesday, October 26, 2010 at 6:37pm
You had the right idea but where is the pH 9.29 part? And there must be a concn Fe^+2 in there somewhere.

Remember talking about Qsp?
Convert pH = 9.29 to OH^-, then multiply
Qsp = (Fe^+2)(OH^-)^2
Now compare Qsp with Ksp and you will know if a ppt occurs. Again, you must have Fe^+2 concn in the problem?

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