Question

What is coagulation? Explain.

Answer 1

Hint: There exist various repulsive forces among the colloidal particles in a system. These repulsive forces among the charged particles do not allow them to settle. If, somehow, these repulsive forces are removed between the charged particles, the colloid particles can easily precipitate or coagulate.

Complete answer:
 As we know that the stability of a lyophobic sol is because of the adsorption of the positively charged or negatively charged ions by the dispersed particles. There exist several repulsive forces among these charged particles which do not favor their settlement. If, somehow, these charges on the particles are removed, there will be no force of repulsion that shall exist in between the particles, thus, there will be nothing that would separate the particles anymore. In such cases, the particles aggregate or flocculate and settle down under the action of the force of gravitation. Thus, the precipitation or flocculation of the dispersed phase particles is known as coagulation.
The coagulation of dispersed phase particles in the lyophobic sols can be achieved by these methods:
(i) By addition of electrolyte.
(ii) By electrophoresis.
(iii) By mixing two oppositely charged sols.
(iv) By boiling.
(v) By repeated dialysis.
The coagulation of dispersed phase particles in the lyophilic sols can be achieved by these methods:
(i) By addition of electrolyte.
(ii) By adding suitable solvent.

Note:
The lyophilic sols are stable due to less charged particles and high solvation of the colloid particles. If these factors are removed then the lyophilic sols can be coagulated easily. The coagulation of the lyophobic sols is less stable as compared to lyophilic sols.