1. Solubility Equilibria
Ksp

2. 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

3. 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.

4. 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

5. 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

6. 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