If I know, say, the mass of precipitated PbCrO4 when I mixed PbCl2 solution (100mL exact) and K2CrO4 (excess), how would I go about calculating the original concentrations of Pb2+ and Cl- in the original PbCl2 solution?

Again, all I know is the mass of precipitated PbCrO4…this isn’t good that I can’t do this, eh?

Here’s how I tried to solve it:

I used the molar mass of PbCrO4 to determine that at the end I had .0022mol of Pb2+ ions. I said this was the original concentration in solution, but I know that is wrong, because not all Pb2+ precipitated (this is one reaction that has a Ksp, that much I know, and that Ksp is not overwhelmingly product-favored).

Can you help me get to where I need to be? Thank you!