A Simple Problem: Solubility of Pb(IO3)2 in Water

 A Simple Problem: Solubility of Pb(IO3)2 in Water

When an insoluble compound such as Pb(IO3)2 is added to a solution a small por- tion of the solid dissolves. Equilibrium is achieved when the concentrations of Pb2+ and IO3– are sufficient to satisfy the solubility product for Pb(IO ) . At equilibrium the solution is saturated with Pb(IO3)2. How can we determine the concentrations of Pb2+ and IO3–, and the solubility of Pb(IO ) in a saturated solution prepared by adding Pb(IO3)2 to distilled water?


As equilibrium is established, two IO3– ions are produced for each ion of Pb2+. If we assume that the molar concentration of Pb2+ at equilibrium is x then the molar con- centration of IO3– is 2x. To help keep track of these relationships, we can use the following table.


Substituting the equilibrium concentrations into equation 6.33


The equilibrium concentrations of Pb2+ and IO3–, therefore, are

[Pb2+]= x = 4.0 x 10–5 M

[I–]= 2x = 7.9 x 10–5 M

Since one mole of Pb(IO3)2 contains one mole of Pb2+, the solubility of Pb(IO3)2 is the same as the concentration of Pb2+; thus, the solubility of Pb(IO3)2 is 4.0 x 10–5 M.

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