Question

Give reasons for the following observations:
(i) Physisorption decreases with increase in temperature
(ii) Addition of alum purifies the water
(iii) Brownian movement provides stability to the colloidal solution

Answer 1

1. physisorption is exothermic in nature. Therefore, according to Le-Chatelier's principle, it decreases with an increase in temperature. This means that physisorption occurs more readily at a lower temperature.
   
2. When Alum $\left(\right(A{l}_2\left)\right(S{O}_4{)}_3)$ is added into water it forms a gel-like precipitate such as $Al(OH{)}_3$.This floc attracts other fine particles and suspended material in raw water and settles down at bottom of a container.
3. Brownian movement explains the force of gravity acting on colloidal particles. This helps in providing stability to colloidal sols by not allowing to settle down.