Solubility Product
In this experiment you will determine the solubility product constant (Ksp) of an insoluble salt.
A solution of KI will be titrated with Pb(NO3)2. When a saturated solution of PbI2 is reached, a yellow
precipitate of PbI2 will be observed. From the known concentrations of the KI and Pb(NO3)2 solutions,
the concentrations of I- and Pb2+ can be determined at the point of precipitation of PbI2 and the Ksp
calculated according to the following equation.
2 KI(aq) + Pb(NO3)2(aq)


PbI2(s) +
2KNO3(aq)
Write the net ionic equation for the formation of PbI2.
Calculate the molarity for the solutions prepared by dissolving 4.46g Pb(NO3)2 in 10.0 L of deionized
H2O and 4.48g KI in 1.00 L of deionized H2O.
Procedure:
Add 10 ml of KI to a 50ml Erlenmeyer flask from a repipet.
Fill a burette with Pb(NO3)2 and titrate the KI solution to the with 1ml and stop and swirl the flask
for 1 minute. Then finish the titration until the endpoint, this is where the solution starts to turn yellow.
Repeat this process three times.
Data:
mL of Pb(NO3)2 added
Trial 1
Trial 2
Trial 3
Average
Analysis:
Find the K equation for the formation of PbI2.
Find the Ksp for PbI2.
Calculations:
1) Write the Ksp expression for equilibria of these slightly soluble compounds in aqueous solution:
a. Ag2CrO4 (s)


2Ag+1 (aq) + CrO4-2 (aq)
Ksp =
b. CaCO3 (s)


Ca+2 (aq) + CO3-2 (aq)
Ksp =
c. Mg3(PO4)2 (s)


3 Mg+2 (aq) + 2 PO4-3 (aq)
Ksp =
2) Calculate the solubility of silver chloride in moles per liter.
Ksp for AgCl is 1.77 x 10-10
AgCl


+
Ag + Cl
-
3) Calculate the maximum concentration of chloride ion that can exist in a solution which is 0.002
M Ag+ without precipitation.
Ksp of AgCl = 1.77 x 10-10
AgCl


+
Ag + Cl
-
4) Calculate the solubility in moles per liter of Ba3(PO4)2. Ksp of barium phosphate is 6 x 10-39
Ba3(PO4)2


3Ba2+ + 2PO43-
5) The pH of a saturated Mg(OH)2 solution is 9.87163.
a. Calculate the [OH-1] in the solution.
b. Calculate the [Mg+2] in the solution.
c. Calculate the Ksp of Mg(OH)2.