Question

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

Answer 1

(i) When a beam of light is passed through a colloidal sol, colloidal particles scatter light and we can see the path of light. Thus, Tyndall effect is observed.

(ii) When an electrolyte, $NaCl$ is added to hydrated ferric oxide sol.
$NaCl$ provides colloidal particles which coagulate oppositely charged ferric hydroxide colloidal particles bearing positive charge.

(iii) When electric current is passed through a colloidal sol, the colloidal particles move towards oppositely charged electrode, where they lose their charge and are coagulated. The process is known as electrophoresis.