Posted by Chemistry Confused on Monday, April 19, 2010 at 3:07pm.
Calculate the molar solubility of barium thiosulfate in 0.0045 M Na2S2O3(aq). (Hint: Check any simplifying assumptions that you make.)

Chemistry  DrBob222, Monday, April 19, 2010 at 3:35pm
BaS2O3 ==> Ba^+2 + S2O3^2
Ksp = (Ba^+2)(S2O3^2)
If you call solubility BaS2O3 = S, then S2O3^2 = S from BaS2O3 and 0.0045 from Na2S2O3 for a total of S+0.0045M. Substitute into Ksp and solve for S. I assume from the hint that you can not make the assumption that S+0.0045 = 0.0045; i.e., that S is not negligible compared to 0.0045 which probably means a quadratic equation solution.