Solubility Equilibria Name ________________ Chem Worksheet 18-7 Ionic solids that are described as insoluble or slightly soluble can be described using the concept of equilibrium. An insoluble solid reaches a state of equilibrium with its dissolved ions when there are very small amounts of ions present. The solubility equilibrium equation for an insoluble ionic compound is written below. The forward reaction is shows the dissolution of Ni(OH)2 into nickel (II) and hydroxide ions while the reverse reaction shows the precipitation of Ni(OH)2 from the ions. Ni2+ (aq) + OH– (aq) Ni(OH)2 (s) This equation has a very small equilibrium constant. In other words, an equilibrium is reached when the reaction has produced a very small concentration of dissolved ions. The amount of the nickel (II) hydroxide compound that dissolves is described as the molar solubility of the compound. Example What is the molar solubility of silver carbonate, Ag2CO3, given that it has a Ksp = 6.3 × 10-12. - Write the solubility equilibrium equation: - Write the solubility product expression: - Create a table to organize concentrations: 2Ag+ (aq) + CO32– (aq) Ag2CO3 (s) Ksp Ag2CO3 (s) initial change equil. - Substitute equilibrium concentrations and solve: (solubility) x = [Ag+]2[CO32–] 2Ag+ (aq) + CO32– (aq) 0M 0M + 2x +x 2x x Ksp = [Ag+]2[CO32–] -12 6.3 × 10 = (2x)2(x) -12 6.3 × 10 = 4x3 x (solubility) = 1.1 × 10-4 mol/L Solve the following equilibrium problems. Show all work and report answers with units. 1. Write the solubility equilibrium equation for calcium sulfate, CaSO4. 2. Write the solubility equilibrium equation for magnesium hydroxide, Mg(OH)2. 3. Write the solubility product expression for strontium carbonate, SrCO3. 4. Write the solubility product expression for copper (II) phosphate, Cu3(PO4)2. 5. What is the molar solubility of silver bromide, AgBr, at 25ºC? (Ksp = 5.0 × 10-13) 6. What is the molar solubility of tin (II) hydroxide, Sn(OH)2, at 25ºC? (Ksp = 1.4 × 10-28) 7. A sample of lead (II) carbonate, PbCO3, is added to water at 25ºC. At equilibrium the concentration of lead (II) ions is 2.7 × 10-7 M. What is Ksp for PbCO3? © John Erickson, 2005 8. A sample of aluminum hydroxide, Al(OH)3, is added to water at 25ºC. At equilibrium the concentration of Al3+ ions is 2.6 × 10-9 M. What is Ksp for Al(OH)3? 9. What are the equilibrium concentrations of Mg2+ and CO32- in a saturated solution of magnesium carbonate, MgCO3, at 25ºC? (Ksp = 3.5 × 10-8) 10. What are the equilibrium concentrations of Ag+ and CrO42- in a saturated solution of silver chromate, Ag2CrO4, at 25ºC? (Ksp = 1.1 × 10-12) 11. What are the equilibrium concentrations of Pb2+ and AsO43- in a saturated solution of lead (II) arsenate, Pb3(AsO4)2, at 25º? (Ksp = 4.0 × 10-36) WS18-7SolubilityEquilibrium