Question

Explain what is observed when:
(i) an electrolyte, KCl, is added to a hydrated ferric oxide sol.
(ii) an electric current is passed through a colloidal solution.
(iii) a beam of strong light is passed through a colloidal solution.

Answer 1

(i) The positively charged colloidal particles of Fe(OH)₃ get coagulated by the oppositely charged Cl- ions provided by KCl.
(ii) On passing direct current, colloidal particles move towards the oppositely charged electrode where they lose their charge and get coagulated.
(iii) Scattering of light by the colloidal particles takes place and the path of light becomes visible (Tyndall effect).