Ksp Calculation

[Seinfeld4]

1. The problem statement, all variables and given/known data

Hi,

I need to calculate the Ksp of Ag2CrO4 based on experimental data.

During the experiment, 1.25g of pure copper was placed in a 1.00 L solution of silver chromate. When the copper was extracted, only 1.24g remained.
Balanced chemical equation: Cu + Ag2CrO4 --> CuCrO4 + 2Ag

3. The attempt at a solution

Here's what I did:

mole of copper = 0.01g / 63.546
= 1.57 * 10^-4

Since volume is 1.00 L, the number of moles is equal to the concentration.
There are 2 moles of Ag and 1 mole of CrO4 for every mole of copper, so:

Ksp = (1.57 * 10^-4) (3.15 * 10^-4) (3.15 * 10^-4)
= 1.56 * 10^-11

But this doesn't seem correct because the actual value is 1.1 * 10^-12.
This would give me a percentage error of over 1000%...

Any help would be much appreciated.

[Borek]

Your approach looks correct and the answer seems to be consistent with the data given.

I don't like this question. I wonder how they extracted the copper. Solid left after reaction completed should weigh more, not less.

[Seinfeld4]

Ok, I thought I was doing it properly. I'm not sure why they made a question that produced a % error greater than 1000. Anyways, thanks Borek!