Solubility Product Constant:

1

• Solubility Product Constant

• A saturated solution of any ionic compound in a
  closed system is an example of chemical
  equilibrium.

eg
Cu2SO42-
K
Saturated concentrations
CuSO4
Concentration is constant
CuSO4K Cu2SO42-
Ksp Cu2SO42-

• Ksp is the solubility product constant.
• Large Ksp ? high solubility
• Small Ksp ? low solubility

2

• Even ionic compounds with very low solubility
  have Ksp values.

eg
The Ksp for limestone (CaCO3) is 4.8 x 10-9,
calculate its solubility.
I
0
0
C
x
x
E
x
x
Ksp Ca2CO32-
4.8 x 10-9 x2
x 6.9 x 10-5 M

• Even though we consider limestone to be
  insoluble, it does dissolve a very small amount.

3
eg
Ksp 8.3 x 10-9 for PbI2. What is the
concentration of Pb2 in a saturated solution of
PbI2?
I
0
0
C
x
2x
E
x
2x
Ksp Pb2I-2
x 1.3 x 10-3 M
8.3 x 10-9 (x)(2x)2
Pb2 1.3 x 10-3 M
8.3 x 10-9 4x3
Note that saturated concentration of Pb2 is the
same as the solubility of PbI2. The saturated
concentration of I- is twice the solubility of
PbI2.