Special Cases for Ksp

Comparing Solubilities from Ksp values Easy ones – contains same number of dissolved particles AgI (s)  Ag + (aq) + I – (aq) Ksp = 1.5 x 10 -16 CaSO4 (s)  Ca 2+(aq) + SO4 2-(aq) Ksp = 6.1 x 10 -5 Which one is more soluble? Largest value is the most soluble

Not the same number of dissolved particles. PbF2 (s)  (X)(2X)2 = 4 x 10 -8 SrSO4 (s)  (X)(X) = 3.2 x 10 -7 Solubilities from above calculations. PbF2 (s) = 0.00215 M SrSO4 (s) = 0.000057 M Pb2+(aq) + 2 F-(aq) Ksp = 4 x 10-8 Sr2+ (aq) + SO4 2–(aq) Ksp = 3.2 x 10-7 PbF2 is more soluble even though it has a smaller Ksp value

Common Ion Effect Ag2CrO4 solution mixed with 0.10 M AgNO3 Calculate the solubility of this solution Ag2CrO4 (s)  2 Ag +(aq) + CrO4 2-(aq) Ksp = 9.0 x 10 -12 I ? 0.10 M 0 C +2X +X E 0.10 +2X X Ksp = [Ag+]2[CrO42-] Assume X = 0 and solve X = 9.0 x 10 -10 M Just Ag2CrO4 = 1.3 x 10 -4 M = (0.10 + 2X)2(X) = 9.0 x 10 -12

Will a Precipitate form? Find Q, which is found the same as Ksp. Compare Q to Ksp , if Q > Ksp, then ppt forms Mix 0.00286 M Ce 3+ with 0.00571 M IO3 – Write dissociation of would be solid. Ce(IO3)3 (s)  Ce 3+(aq) + 3 IO3 – (aq) Q = [Ce 3+][IO3 -]3 Ksp = 1.9 x 10 -10 Q > Ksp so solid forms = [0.00286][0.00571]3 = 5.32 x 10 -10