October 8, 2015

Homework Help: -Chemistry-

Posted by Linda on Monday, May 14, 2007 at 10:56am.

I have asked this question before but I was wondering if I solved this question correctly.

A solution of barium chromate is prepared by dissolving 6.3 x 10-3 g of this yellow solid in 1.00 L of hot water. Will solid barium chromate precipitate upon cooling to 25C?

You want to compare Qsp to Ksp (at 25o C.)
BaCrO4 (s) ==> Ba + CrO4

Ksp = BaCrO4= 1.1710-10
6.3E-3g/253.33molar mass BaCrO4 = 2.49 x 10-5 mols BaCrO4 in 1
Qsp = (x)(x) = 6.18 x10-10

I feel that I did something wrong (the answer to my question before included silver chromate not barium chromate, hence my confusion)

You haven't answered the question. Will BaCrO4 ppt upon cooling?
You haven't done anything wrong. All of the numbers look good to me. You just need the conclusion. OR tell us what you are confused about.
Another way of solving the problem is to calculate the solubility of BaCrO4 at 25 degrees C from Ksp and compare that molar solubility with the initial hot water molar solubility OR change the molar solubility of BaCrO4 to grams and compare directly with grams BaCrO4 dissolved in the hot water.

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