# Solubility Equilibria

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Solubility Equilibria
Ksp

Solubility & Solubility Product
Even “insoluble” salts dissolve somewhat in water insoluble = less than 0.1 g per 100 g H2O The solubility of insoluble salts is described in terms of equilibrium between undissolved solid and aqueous ions produced AB (s)  a A+(aq) + b B-(aq) Equilibrium constant called solubility product Ksp = [A+]a [B-]b If undissolved solid is in equilibrium with the solution, the solution is saturated Larger K = More Soluble for salts that produce same the number of ions 22

Ksp 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.

Calculate the solubility of AgI in water
Example Calculate the solubility of AgI in water at 25°C if the value of Ksp = 1.5 x 10-16 Determine the balanced equation for the dissociation of the salt AgI (s)  Ag+ (aq) + I- (aq) Determine the expression for the solubility product Same as the Equilibrium Constant Expression Ksp = [Ag+] [I-] 23

Calculate the solubility of AgI in water
Example Calculate the solubility of AgI in water at 25°C if the value of Ksp = 1.5 x 10-16 Define the concentrations of dissolved ions in terms of x AgI (s)  Ag+ (aq) + I- (aq) Stoichiometry tells us that we get 1 mole of Ag+ and 1 mol I- for each mole of AgI dissolved Let x = [Ag+], then [I-] = x 24

Calculate the solubility of AgI in water
Example Calculate the solubility of AgI in water at 25°C if the value of Ksp = 1.5 x 10-16 Plug 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 M 25