When salt is added to a solution containing either the same cation or anion there will be changes in the solubility because of what is commonly known as common ion effect. This is so because the solubility of the salt added is affected by the common ion which is already present in the solution.
The solubility of a salt is considerably reduced when it is dissolved in a solution that already contains one of its ions, rather than in a pure solvent.
For example, is salt such as CaF2 is dissolved in a solution already containing Ca2+ ions, the dissociation equilibrium will shift toward the production of the solid salt. This reduction in solubility called the common ion effect and is another example of Le Chatelier’s principle.