What effect does the common ion effect have on the solubility of salts?

The common ion effect refers to the phenomenon in which the solubility of a salt is decreased when a compound containing a common ion is added to the solution. This effect is rooted in Le Chatelier's principle, which states that if a system at equilibrium is subjected to a change in conditions, the equilibrium will shift to counteract that change.

For example, consider a salt like silver bromide (AgBr). When AgBr dissolves in water, it dissociates into silver ions (Ag⁺) and bromide ions (Br⁻). Now, if you add sodium bromide (NaBr), which also provides Br⁻ ions to the solution, the increased concentration of Br⁻ will shift the equilibrium of the AgBr dissociation towards the solid state to reduce the concentration of Br⁻, thereby reducing the solubility of AgBr.

Thus, the presence of a common ion effectively suppresses the dissolution of the salt, leading to a reduced solubility. This principle is essential in various applications including qualitative analysis and understanding the behavior of electrolytes in different conditions.