Peptization: The process of converting a freshly prepared precipitate into colloidal form by the addition of a suitable electrolyte is called peptisation. The electrolytes used for the purpose are called peptising agents. E.g. if freshly prepared ferric hydroxide precipitate are treated with a small amount of FeCl3 solution (electrolyte), a reddish brown coloured colloidal solution Fe(OH)3 is formed. In this case, FeCl3 is peptising agent.
Fe(OH)3 + Fe3+ —————> Fe(OH)3Fe3+
PPT Colloids