Question

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

Answer 1

(i) When $NaCl$ is added to ferric oxide sol, it dissociates to give $N{a}^{+}$ and $C{l}^{-}$­ ions. Particles of ferric oxide solution are positively charged. Thus, they get coagulated in the presence of negatively charged $C{l}^{-}$ ions.

(ii) When a beam of light is passed through a colloidal solution, then a scattering of light is observed. This is known as the Tyndall effect. This scattering of light illuminates the path of the beam in the colloidal solution.