What is meant by coagulation of a colloidal solution? Describe briefly any three methods by which coagulation of lyophobic sols can be carried out.

Coagulation is the destabilization of Colloids by neutralizing the electric charge of the dispersed phase particles, which results in aggregation of the colloidal particles.

Aggregation is a formation of groups of particles (aggregates) bonded to each other by van der Waals or other intermolecular forces.
Aggregation usually refers to solid particles.
If a coagulation of a liquid or gaseous dispersed phase occurs the term coalescence instead of aggregation is used. Coalescence is characterized by disappearance of the boundary between the particles resulting in the reduction of the interfacial area.
In a stable colloid system the dispersed particles are electrically (commonly negatively) charged. Two charged particles repeal each other preventing collision and aggregation.
When the charges are neutralized the particles may collide and bond to each other.

The coagulation of the lyophobic sols can be carried out by following methods.

(1) By electrophoresis: In electrophoresis the colloidal particles move towards oppositely charged electrode. When these come in contact with the electrode for long these are discharged and precipitated.

(2) By mixing two oppositely charged sols : When oppositely charged sols are mixed in almost equal proportions, their charges are neutralised. Both sols may be partially or completely precipitated as the mixing of ferric hydroxide (+ve sol) and arsenious sulphide (–ve sol) bring them in precipitated form. This type of coagulation is called mutual coagulation or meteral coagulation.

(3) By boiling: When a sol is boiled, the adsorbed layer is disturbed due to increased collisions with the molecules of dispersion medium. This reduces the charge on the particles and ultimately they settle down to form a precipitate.

The phenomenon of the precipitation of a colloidal solution by the addition of the excess of an electrolyte is coagulation or flocculation .

Dear Student,
Please find below the solution to your problem.

Coagulation is the destabilization of Colloids by neutralizing the electric charge of the dispersed phase particles, which results in aggregation of the colloidal particles. Aggregation is a formation of groups of particles (aggregates) bonded to each other by van der Waals or other intermolecular forces. Aggregation usually refers to solid particles. If a coagulation of a liquid or gaseous dispersed phase occurs the term coalescence instead of aggregation is used. Coalescence is characterized by disappearance of the boundary between the particles resulting in the reduction of the interfacial area. In a stable colloid system the dispersed particles are electrically (commonly negatively) charged. Two charged particles repeal each other preventing collision and aggregation. When the charges are neutralized the particles may collide and bond to each other. The coagulation of the lyophobic sols can be carried out by following methods.
(1) By electrophoresis: In electrophoresis the colloidal particles move towards oppositely charged electrode. When these come in contact with the electrode for long these are discharged and precipitated.
(2) By mixing two oppositely charged sols : When oppositely charged sols are mixed in almost equal proportions, their charges are neutralised. Both sols may be partially or completely precipitated as the mixing of ferric hydroxide (+ve sol) and arsenious sulphide (–ve sol) bring them in precipitated form. This type of coagulation is called mutual coagulation or meteral coagulation.
(3) By boiling: When a sol is boiled, the adsorbed layer is disturbed due to increased collisions with the molecules of dispersion medium. This reduces the charge on the particles and ultimately they settle down to form a precipitate.

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