Question

Method(s) for coagulation of lyophobic sols include:

• A. Electrophoresis
• B. Mixing two oppositely charged sols
• C. Boiling
• D. All of the above.

Answer 1

The correct option is D All of the above.

Coagulation is the process of aggregation of colloidal particles into an insoluble precipitate by the addition of some suitable electrolyte.

Methods for coagulation of lyophobic sol:

(i) By electrophoresis: The colloidal particles move towards oppositely charged electrodes, get discharged and precipitated.

(ii) By mixing two oppositely charged sols: When oppositely charged sols are mixed in equal amount their charges get neutralised and result in partial or complete precipitation. This type of coagulation is called mutual coagulation. Ex: Mixing of hydrated ferric oxide (positive sol) and arsenous sulphide (negative sol) bring them in the precipitated forms.

(iii) 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 leads to settling down in the form of a precipitate.