Question

Peptising agent is added to convert precipitate into colloidal solution. Explain with an example.

Answer 1

1. Ions either positive or negative of peptising agent (electrolyte) are adsorbed on the particles of the precipitate. They repel and hit each other and break the particles of the precipitate into colloidal size.

2. 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,
\[\ce{\underset{(Precipitate)}{AgCl} ->[HCl] \underset{(Colloid)}{AgCl}}\]