Peptization is the method of producing stable colloids using an electrolyte to split up and distribute a precipitate into the colloids. Peptization utilizes the charges to produce colloids from the precipitate. The electrolyte used in the process is called a peptizing agent.
Example: When the ferric chloride is added to the precipitate of ferric hydroxide, the hydroxide precipitate transfer to the sol by absorbing ferric ions. In simple words, Fe3+ is absorbed on Fe(OH)3 and splits into colloids.
Why peptizing agent is added to convert the precipitate into a Colloidal solution?
Ions either (+ve or –ve) of the peptizing agent (electrolyte)are adsorbed on the particles of the precipitate. They repel and hit each other breaking the particles of the precipitate into colloidal size.
For example, when we add a small volume of very dilute hydrochloric acid solution peptising agent to a fresh precipitate of silver chloride, it leads to the formation of silver chloride colloidal solution.