what is common ion effect?

The common ion effect is the decrease in the ionization of a weak electrolyte when a strong electrolyte containing a common ion is added to the solution.

A common ion is an ion that is present in both the weak electrolyte and the added strong electrolyte.

Example:

Consider acetic acid:

CH₃COOH ⇌ CH₃COO⁻ + H⁺

When sodium acetate (CH₃COONa) is added, it releases CH₃COO⁻ ions. The increase in acetate ions suppresses the ionization of acetic acid, shifting the equilibrium to the left.

Key Points:

1. Occurs in solutions containing a common ion.

2. Reduces the ionization of weak acids or weak bases.

3. Explained by Le Chatelier's Principle.

4. Used in the preparation of buffer solutions.

In simple terms: The common ion effect is the reduction in the ionization of a weak electrolyte caused by adding another substance that provides the same ion.