Passage VI (Questions 29-35)
We have seen that when a salt dissolves in pure water, the expression for Ksp can be used to solve for the concentration of the ions. For example, for AgCl,
Ksp = [Ag+][Cl-]
Since in pure water, every silver or chloride ion results from a dissociation, either concentration may be used to calculate the solubility.
The situation is different if there is another source of either ion. The table below gives solubility data for various salts in pure water (column 3) and for a solution containing 0.1 mol/L of the cation in the original salt. For example, for BaSO4, the last column refers to solubility in 0.1 M Ba2+.