The coagulation of the lyophobic sols can be carried out by

Options

A. electrophoresis
B. persistent dialysis
C. addition of electrolytes
D. all of these

Answer

D

Explanation

The stablity of the lyophobic sols is due to the presence of charge is removed, the particles will come nearer to each other to form aggregates (or coagulate) and settle down under the force of gravity.
During elecrophoresis,the colloidal particles move towards oppositely charged electrodes,get discharged and precipitated.On prolonged dialysis, traces of the elecrolyte present in the sol (needed for their stabilization) are removed almost completely and the colloids become unstable and ultimately coagulate.
When excess of an elecrolyte is added,the colloidal particles are precipitated.The reason is that colloids interact with ions carrying charge opposite to that present on themselves.This causes neutralization leading to thier coagulation.The ion responsible for neutralization of charge on the particles is called the coagulating ion. A negative ion causes the precipitation of positively charged sol and vice versa.
We can also coagulate lyphobic sols by mixing two oppositely charged sols and by boiling.When mixed in almost equal proportions,oppositely charged sols neutralize their charges and get partially or completely precipitated.For example,mixing of hydrated ferric oxide (+ve sol) and arsenious sulphide (-ve sol) bring them in the precipitated forms.This type of coagulation is called mutual coagulation.
When a sol os boiled,the adsorbed layer is disturbed due to increased collisions with the particles of dispersion medium. This reduces the charge on the particles and ultimately lead to settling down in the form of a precipitate.