2Solubility & Solubility Product Even “insoluble” salts dissolve somewhat in waterinsoluble = less than 0.1 g per 100 g H2OThe solubility of insoluble salts is described in terms of equilibrium between undissolved solid and aqueous ions producedAB (s) a A+(aq) + b B-(aq)Equilibrium constant called solubility productKsp = [A+]a [B-]bIf undissolved solid is in equilibrium with the solution, the solution is saturatedLarger K = More Solublefor salts that produce same the number of ions22
3Ksp is the solubility product equilibrium constant at a given temperature. The solubility of a substance represents an equilibrium position for the system.First, write the dissociation equation of the ionic compound in water, including states.Then, set up the expression for K (you will only have the ions in this expression since the salt is a solid).Solve for a numerical value of Ksp using given data.Remember that for every one formula unit that breaks up, you will get equal molar concentrations for ions that are in a 1:1 ratio in the compound. If the ratio is not 1:1, adjust accordingly.
4Calculate the solubility of AgI in water ExampleCalculate the solubility of AgI in waterat 25°C if the value of Ksp = 1.5 x 10-16Determine the balanced equation for the dissociation of the saltAgI (s) Ag+ (aq) + I- (aq)Determine the expression for the solubility productSame as the Equilibrium Constant ExpressionKsp = [Ag+] [I-]23
5Calculate the solubility of AgI in water ExampleCalculate the solubility of AgI in waterat 25°C if the value of Ksp = 1.5 x 10-16Define the concentrations of dissolved ions in terms of xAgI (s) Ag+ (aq) + I- (aq)Stoichiometry tells us that we get 1 mole of Ag+ and 1 mol I- for each mole of AgI dissolvedLet x = [Ag+], then [I-] = x24
6Calculate the solubility of AgI in water ExampleCalculate the solubility of AgI in waterat 25°C if the value of Ksp = 1.5 x 10-16Plug the ion concentrations into the expression for the solubility product and solve for Ksp[Ag+] = [I-] = x[Ag+] = 1.2 x 10-8 mol/L = [AgI]The solubility of AgI (at 25°C) = 1.2 x 10-8 M25