Solubility Equilibria Solubility product (Ksp) – equilibrium constant; has only one value for a given solid at a given temperature. Solubility – an equilibrium position. Bi2S3(s) 2Bi3+(aq) + 3S2–(aq) Copyright © Cengage Learning. All rights reserved

Explain. If yes, explain and verify. If no, provide a counter-example. CONCEPT CHECK! In comparing several salts at a given temperature, does a higher Ksp value always mean a higher solubility? Explain. If yes, explain and verify. If no, provide a counter-example. No. In order to relate Ksp values to solubility directly, the salts must contain the same number of ions. For example, for a binary salt, Ksp = s2 (s = solubility); for a ternary salt, Ksp = 4s3. Copyright © Cengage Learning. All rights reserved

EXERCISE! Calculate the solubility of silver chloride in water. Ksp = 1.6 × 10–10 Calculate the solubility of silver phosphate in water. Ksp = 1.8 × 10–18 a) 1.3×10-5 M b) 1.6×10-5 M Copyright © Cengage Learning. All rights reserved

Calculate the solubility of AgCl in: EXERCISE! Calculate the solubility of AgCl in: Ksp = 1.6 × 10–10 100.0 mL of 4.00 x 10-3 M calcium chloride. 100.0 mL of 4.00 x 10-3 M calcium nitrate. a) 2.0×10-8 M Note: [Cl-] in CaCl2 is twice the [CaCl2] given. 100.0 mL is not used in the calculation. b) 1.3×10-5 M Copyright © Cengage Learning. All rights reserved

Precipitation (Mixing Two Solutions of Ions) Q > Ksp; precipitation occurs and will continue until the concentrations are reduced to the point that they satisfy Ksp. Q < Ksp; no precipitation occurs. Copyright © Cengage Learning. All rights reserved

Selective Precipitation (Mixtures of Metal Ions) Use a reagent whose anion forms a precipitate with only one or a few of the metal ions in the mixture. Example: Solution contains Ba2+ and Ag+ ions. Adding NaCl will form a precipitate with Ag+ (AgCl), while still leaving Ba2+ in solution. Copyright © Cengage Learning. All rights reserved

Separation of Cu2+ and Hg2+ from Ni2+ and Mn2+ using H2S At a low pH, [S2–] is relatively low and only the very insoluble HgS and CuS precipitate. When OH– is added to lower [H+], the value of [S2–] increases, and MnS and NiS precipitate. Copyright © Cengage Learning. All rights reserved