Posted by Mig on Sunday, June 5, 2011 at 8:33am.
You made up a saturated solution of calcium sulfate (CaSO4). The temp is 25 degrees Celsius. You then add 5.00*10^3 of sodium sulfate (NaSO4). What are the concentrations of calcium and sulfate after equilibrium is reached? The pKs of CaSO4 is 4.58.
I know the Ks of CaSO4 to be 10^(4.58) which equals 2.63E5 but then what?

Chem  DrBob222, Sunday, June 5, 2011 at 9:39pm
CaSO4 ==> Ca^2+ + SO4^2
Ksp = (Ca^2+)(SO4^2) = 2.63E5
From CaSO4 alone;
(Ca^2+) = x
(SO4^2) = x
Na2SO4 ==> 2Na^+ + SO4^2
You added 5.00E3 WHAT? Is that molar? If so, then Na^2+ = 2*5.00E3M
and (SO4^2) = 0.005M
Plug all of this into Ksp for CaSO4.
Ksp = (x)(x+0.005) = 2.63E5
Solve for x, then x + 0.005.