Question

what do you mean by protection of colloids

Answer 1

Lyophilic sols are more stable than the lyophobic sols. Lyophobic sols can be easily coagulated by the addition of small quantity of an electrolyte. However, when a lyophilic colloid is added to any lyophobic sol it becomes less sensitive towards electrolytes. Thus, lyophilic colloids can prevent the coagulation of any lyophobic sol.
This phenomenon of preventing the coagulation of a lyophobic sol due to the addition of some lyophilic colloid is called sol protection, or protection of colloids.
The lyophilic colloid which prevents the coagulation of a lyophobic sol is called a protective colloid.
The efficiency of any protective Colloid is expressed in terms of its gold number.
The gold number is defined as, “Weight of the dried protective agent in milligrams, which when added to 10 mL of a standard gold sol to prevent a colour change from red to blue on the addition of 1 mL of 10 percent sodium chloride solution, is equal to the gold number of that protective colloid.”
Thus smaller is the gold number, higher is the protective action of the protective agent.