E9.3+Water+and+Soil+(HL)

__Water and Soil__
Salt can be formed from metal M and non metal X MX (s) = M+ (aq) + X-(aq) The equilibrium expression for salt equation is Ksp = measure of solubility = [M+] x [X-] / [MX], however MX will be 0 because salt is a solid and , solid has no concentration = [M+] x [X-]

Metal sulfides have very low solubility products, so to preciptate heavy metal ions is by bubbling hydrogen sulfide through polluted water. The solubility product can be used to calculate the amount of a metal ion that is remain in solution after precipitation. PbS solubility is 1.30 x 10-28 (very insoluble) PbS (s) = Pb2+(aq) + S2- (aq) Ksp = [Pb2+] x [S2-] but [Pb2+] = [S2-] Ksp = 1.30 x 10-28 = [Pb2+] ^2 [Pb2+] = 1.14 x 10-14 mol dm-3