Question

What are protective colloids and how do they protect a hydrophobic sol?

Answer 1

Protective colloids are lyophilic colloids such as gelatin, gum arabic, and starch, which, when added in small amounts to lyophobic sols, prevent their coagulation. They do so by adsorbing onto the surface of the lyophobic colloidal particles and forming a protective layer around them. This layer prevents the action of electrolytes that would otherwise cause the particles to aggregate. The effectiveness of a protective colloid is measured by its gold number; the smaller the amount required to prevent the coagulation of gold sol, the greater its protective power.