Solubility Product & pH: Common Ion Effect

Solubility Product & pH

Common Ion Effect

• The common ion effect is a phenomenon where the solubility of a slightly soluble salt is decreased by the addition of a common ion.
• A common ion is an ion that is already present in the solution, often from a different source.
• The common ion effect occurs because the added ion shifts the equilibrium of the solubility reaction, reducing the solubility of the salt.

Factors Affecting the Common Ion Effect

• Concentration of the common ion: Increasing the concentration of the common ion increases the common ion effect, decreasing the solubility of the salt.
• Solubility product (Ksp): The common ion effect is more pronounced for salts with smaller Ksp values.

Examples of the Common Ion Effect

• Silver chloride (AgCl): Addition of NaCl to a solution of AgCl reduces the solubility of AgCl due to the common ion Cl-.
• Calcium carbonate (CaCO3): Addition of Ca(NO3)2 to a solution of CaCO3 reduces the solubility of CaCO3 due to the common ion Ca2+.

Importance of the Common Ion Effect

• Precipitation reactions: The common ion effect is important in precipitation reactions, where it can be used to control the formation of precipitates.
• Water treatment: The common ion effect is used in water treatment to remove impurities, such as calcium and magnesium ions, by adding a common ion to precipitate out the impurities.