Common Ion

Definition

When a solution contains an ion that is already present in the solid form, it is referred to as a common ion. This can come from either a previously dissolved compound or the dissociation of a partially soluble compound.

Related terms

Solubility Product Constant (Ksp): The equilibrium constant for the dissolution of a sparingly soluble salt. It represents how much of the solid will dissolve in water.

Le Chatelier's Principle: This principle states that when there is a stress applied to a system at equilibrium, it will shift in order to relieve that stress. In this case, increasing the concentration of common ions would be considered a stress on the system.

Precipitation Reaction:

A reaction in which two aqueous solutions combine to form an insoluble solid called a precipitate. Increasing the concentration of common ions can increase the likelihood of precipitation occurring.