The process of removal of an adsorbed substance from the surface on which it is adsorbed is called desorption. It is the reverse of adsorption and can be brought about by heating or by reducing the pressure. The heat energy absorbed weakens the forces binding the molecules of the adsorbent and adsorbate.

Sometimes adsorption may be followed by the dissolution of the adsorbed substance (adsorbate) in the adsorbent, which is passing from the surface into the bulk of the adsorbent (absorption). The process of simultaneous adsorption and absorption is called sorption. For example, dyes also get adsorbed as well as absorbed in the cotton fibres that are sorption takes place.

The absorption of a substance from gaseous medium by solids is referred to as occlusion. During the occlusion, gases are absorbed by the entire volume of the absorbent rather than by the surface. For example, water molecules get trapped in a pocket at the time of silver crystal formation due to the rapid crystallization.

Explain Tyndall effect?

Colloidal solution or sol consists of fine particles invisible to naked eyes. However, when this solution is placed against a dark background and a strong beam of light is passed through it, the light scattered by them can be observed through the ultramicroscope. The path of light can be viewed from a direction at a right angle to that of incident light. The Phenomenon of scattering of light by sol particles is called Tyndall effect. It confirms the heterogeneous nature of the colloidal solution.

What is Brownian movement ?

The Brownian movement in a colloidal system is caused by the unequal bombardment of the molecules of the dispersion medium on the colloidal particles. When more molecules strike the particles on one side, the direction of the motion of particles changes. This is only visible through ultramicroscope. In colloidal solutions, the colloidal particles are in constant zig-zag motion known as Brownian motion. This phenomenon was first observed by Sir Robert Brown in the year 1827.