Give reasons for the following :
(i) Peptizing agent is added to convert a precipitate into a colloidal solution.
(ii) Colloidal gold is used for intramuscular injection.
(iii) Cottrell's smoke precipitator is fitted at the mouth of a chimeny used in factories.

Explanation

(a) Ions (either +ve or -ve) of peptising agent (electrolyte) are adsorbed on the particles of the precipitate. They repel and hit each other breaking the particles of the precipitate inot colloidal size.
(b) It neutralizes the cherge on the carbgon particles which get precipitated and thus gases entering into chimney are free from carbon particles.
(c ) This is done because gold particles have large surface area and easily assimilated into blood which is colloidal.