Question

Lyophilic sols could be coagulated by

• A. Adding an excess of an electrolyte
• B. Adding a suitable solvent that dehydrates the dispersed phase and then adding an electrolyte
• C. Shaking the colloidal solution
• D. Adding more dispersion medium

Answer 1

Answer: (A), (B)

The correct options are
A Adding an excess of an electrolyte
B Adding a suitable solvent that dehydrates the dispersed phase and then adding an electrolyte

There are two principal factors which are responsible for the stability of lyophilic sols - charge and solvation of the colloidal particles. If we manage to remove these two factors, a lyophilic sol can be coagulated. This could be accomplished by

(i) Adding an excess of electrolyte
(ii) Adding a suitable solvent. When solvents such as alcohol and acetone are added to hydrophilic sols, dehydration of dispersed phase occurs. Under this condition, a small quantity of electrolyte can bring about coagulation.

Hydrophilic sols are much more stable than hydrophobic sols and they are not coagulated by shaking or adding more of the dispersion medium.