Solubility Equilibria Objectives: 1.Compare dissolution with precipitation. 2.Describe equilibria for aqueous solutions of ionic solids. Key Terms: dissolution, precipitation, solubility equilibrium, solubility product

Solubility Ionic solids dissolve in polar solvents (water) due to the their charged ends. Since the ionic solid forms a lattice (repeating sequence of positive and negative ions) dissolution of the ionic solid is fairly consistent and predictable. dissolution is the process in which an ionic solid dissolves in a polar solvent saturation is the point where the maximum dissolution has taken place precipitation is the regeneration of the ions in a solution solubility equilibrium is the point where the rate of dissolution is equal to the rate of precipitation

solubility product The solubility product constant represents the ions that can be dissolved in solution – K sp =[Na + ][Cl - ] the smaller the number the less soluble a substance is K sp =[Pb 2+ ] x [CrO 4 2- ] = 1 x

Common Ion Effect If an additional salt with the a similar ion is added, the concentration of the similar ion is reduced due to the common ion effect K sp =[Pb 2+ ] x [CrO 4 2- ] = 1 x – Adding Pb(NO 3 ) 2 to the solution shifts the equilibrium to the left causing precipitation until the concentration of Pb is again K sp = 1 x The precipitation of the excess lead comes at the expense of the chromate ion