How to calculate Q?

Question

If 1.50 mL of 0.69M NH3 areadded to 1.0 L of 1.0 X 10^-3M FeSO4 and a percipitate forms, how do you calculate Q?

I tried
Q=[Fe][SO4]=(1.0 X 10^-3)^2=1.0 X 10^-6
What did I do wrong?

Answer 1

Yes, you are wrong!
First, the precipitated is NOT FeSO4. Rather, is Fe(OH)2.
Second, strictly speaking, even if the precipitation would be FeSO4, the concentration [Fe] and [SO4--] are not 1.0 X 10^-3M any more, since you increased the volume of the solution---in this case is OK---I just want you to be aware of that.