Question

Describe a conspicuous change observed when
(i) a solution of NaCl is added to a sol of hydrated ferric oxide.
(ii) a beam of light is passed through a solution of NaCl and then through a sol.

Answer 1

(i) The positively charged colloidal particles of Fe(OH)₃ get coagulated by negatively charged Cl^– ions provided by electrolyte sodium chloride. 

(ii) The path of light is not visible when light is passed through NaCl solution but visible when light is passed through a sol due to scattering of light by colloidal particles.