Solubility Common Ion Effect

“Common Ion Effect” DIFFICULT If your coffee already has sugar in it, would it be easy or difficult to dissolve MORE sugar? “Common Ion Effect” DIFFICULT

Common Ion Effect: Please write The solubility of a compound is decreased or inhibited if one of its ions is already present in the solvent.

BaCrO4 (s)  Ba2+ (aq) + CrO42- (aq) Please write Consider the equilibrium: BaCrO4 (s)  Ba2+ (aq) + CrO42- (aq) What would happen if BaCl2 were added? BaCl2 would dissolve [Ba2+] would inc. (common ion) Some Ba2+ will react with CrO42- equilibrium shifts left Forming more BaCrO4(s) This means that less BaCrO4 is dissolved hence solubility is decreased

AgCl (s)  Ag+ (aq) + Cl- (aq) If we remove an ion from solution we can shift the equilibrium. One of the ways of doing this is by ppt Please write Consider the equilibrium: AgCl (s)  Ag+ (aq) + Cl- (aq) If Na2S is added: Ag+ + S2-  Ag2S (s) this removes Ag+ ions shifting the equilibrium to the right allowing more AgCl to dissolve increasing solubility

In NaI: Na+ + I- NaI ⇄ PbI2 ⇄ Pb+2 + 2I- 0.1 ⇄ 0.1 0.1 Compare the solubility of PbI2 in H20 and in 0.10M NaI solution. Ksp of PbI2 is 8.5 x 10-9 In H2O: Please write In NaI: NaI ⇄ Na+ + I- PbI2 ⇄ Pb+2 + 2I- 0.1 ⇄ 0.1 0.1 Ksp = [Pb+2] [I-]2 PbI2 ⇄ Pb+2 + 2I- 8.5 x 10-9 = [x][2x]2 x ⇄ x 2x 8.5 x 10-9 = 4x3 Ksp = [Pb+2] [I-]2 PbI2 = 1.29 x 10-3M 8.5 x 10-9 = [x][2x + 0.1]2 8.5 x 10-9 = [x][0.1]2 More PbI2 is dissolved in water !!!! PbI2 = 8.5 x 10-7M