Question

Descibe a conspicous change observed when

(i) a solution of Nacl is added to a 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) Hydrated solution of ferric oxide is a positively charged sol. Upon adding a solution of NaCl into it, coagulation of sol takes place. This is because solution of NaCl has chloride ions that is Cl^- which are oppositely charged as compared to positively charged sol, this neutralizes the surface charges thus allow the particles to coagulate and settle.

(ii) On passing beam of light through NaCl solution intensity of emission decreases. And then this low intensity beam of light is passed through sol, which causes its path to get weakly enlightened