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 a process of aggregating together the colloidal particles so as to change them into large sized particles which ultimately settle as a precipitate. It can also be called as precipitation.

Coagulation is generally brought about by the addition of electrolyte.

When an electrolyte is added to the colloidal solution, the particles of the sol take up the ion which is oppositely charged and thus get neutralised.

Following are the three methods by which coagulation of lyophobic sols can be carried out.

(i) Electrophoresis: In this process, the colloidal particles move towards oppositely charged electrodes and get discharged resulting in coagulation.

(ii) Mixing of two oppositely charged sols: When equal proportions of oppositely charged sols are mixed, they neutralise each other resulting in coagulation.

(iii) Dialysis: By this method, electrolytes present in sol are removed completely and colloid becomes unstably resulting in coagulation.