Question

Which of the following is not a method for coagulation of lyophobic sols?

• A. By electrophoresis
• B. By mixing oppositely charged sols
• C. By adding electrolyte
• D. By adding a protective colloid

Answer 1

The correct option is D By adding a protective colloid

• Lyophilic sols are more stable than lyophobic sols. This is due to the fact that lyophilic colloids are extensively solvated, i.e., colloidal particles are covered by a sheath of the liquid in which they are dispersed.
• Lyophilic colloids have a unique property of protecting lyophobic colloids.
• When a lyophilic sol is added to the lyophobic sol, the lyophilic particles form a layer around lyophobic particles and thus protect the latter from electrolytes. Lyophilic colloids used for this purpose are called protective colloids.
• By adding a protective colloid we can increase the stability of a lyophobic sol and hence option D is the right answer.

We can coagulate a lyophobic sol in different way. They are:

• By electrphoresis.
• Mixing the oppositely charged sols also brings about the coagulation in both the sols.
  
• When we add an electrolyte to a colloid it also coagulates the sols.