What are lyophilic and lyophobic sols ? Give one example of each. Why lyophobic sol is easily coagulated ?

Explanation

Lyophilic Colloids : Lyophilic (or solvent loving) colloids are those in which the dispersion medium possesses great affinity (or love) for the dispersed phase and can be easily prepared by simply shaking dispension.
Examples. Starch, gelatin, glue, agar-agar.
Lyophobic colloids. Lyophobic for solvent hating) colloids are those in which the dispersion medium has no affinity (or hate) for dispersed phase and needs special method for their formation.
Examples. Gold sol, silver sol, arsenic sulphide sol in water.
The stability of hydrophobic sol is only due to the presence of charge on the colloidal particles. If charge is removed, e.g, by addition of suitable electrolystes, the particles will come nearer to each other to form aggregate, i.e., they will coagulate and settle down. On the other hand, the stability of hydrophilic sol is due to charge as well as solvation of the colloidal particles. Both the factors have to be removed to bring about their coagulation.