[Annie_W]

If 100.0 mL of a clear saturated solution of Ag2SO4 is added to 290 mL of a clear saturated solution of PbCrO4 how much precipitate in mg will form? 
For this problem, ignore the back reaction since it will have an insignificant effect on the amount of precipitate that forms.
The molecular weight of PbSO4 is 303.26 g/mol and the molecular weight of Ag2CrO4 is 331.73 g/mol.  Give your answer to three significant figures.

Here is what I did: First I got the equation, PbSO4 -> Pb2+ + SO42-, then I got the Ksp value of PbSO4, Ksp= x^2, x=1.26E-4, I multiplied x by the molar mass of PbSO4, and then I multiplied that answer by total volume(390mL) which in the end, my units came out to be in mg and I got 14.96mg.

I did the exact same for silver chromate, Ag2CrO4- -> 2Ag+ + CrO42- , this time ksp=4x^3, x= 6.50x10^-5, multiply by molar mass of silverchromate, and then multiplied by total volume (390mL) which gave me 8.44mg.

I then added the 2 masses up together to get 14.96mg and 8.44mg to give me 23.4mg. I really really thought I had gotten the correct answer since everything makes sense, the units worked out and the Ksp values made sense with the amount of precipitated yield in both cases. Can anyone please guide me in what I'm doing wrong,

[AWK]

You should recalculate concentrations of sulfate, chormate, silver and lead ions in the final volume and check if any pecipitate of PbSO₄ or Ag₂CrO₄ can be obtained. I guess nothing will happen.