Colloids

Step 1: Definition.
Peptization is the process of converting a freshly precipitated substance (precipitate) into colloidal particles by adding a small amount of suitable electrolyte.
Step 2: Mechanism.
During peptization, the ions of the added electrolyte adsorb on the surface of precipitate particles. This develops an electric charge on the particles and prevents them from coagulating, leading to formation of a stable colloidal sol.
Step 3: Example.
When freshly prepared ferric hydroxide ( ) precipitate is treated with a small amount of ferric chloride ( ) solution, a reddish brown colloidal sol of ferric hydroxide is formed.
Step 4: Importance.
Peptization helps in obtaining colloidal solutions from precipitates without complete dissolution.

Step 1: Recall purification process.
Purification of colloidal sols involves the removal of impurities like electrolytes and small molecules.
Step 2: Analyze options.
- (A) Peptisation: Process of converting precipitate into colloidal sol, not purification.
- (B) Coagulation: Precipitation of colloids, not purification.
- (C) Dialysis: Correct, it removes soluble impurities by diffusion through a semipermeable membrane.
- (D) Flocculation: Causes aggregation of particles, not purification.
Step 3: Conclusion.
Thus, purification of colloidal sols is carried out by Dialysis.

Step 1: Understanding lyophilic colloids.
Lyophilic colloids are those that have an affinity for the dispersion medium (usually water) and are easily hydrated. These colloids are stable in the medium, unlike lyophobic colloids that are unstable and tend to aggregate. Step 2: Analysis of options.
(A) Milk: Milk is a typical example of a lyophilic colloid as it is a water-based system, with fat dispersed in water.
(B) Gum: Gum is a colloid that is not necessarily lyophilic, as it can be more stable in certain conditions without water affinity.
(C) Fog: Fog is a lyophobic colloid, as it consists of liquid droplets dispersed in air.
(D) Blood: Blood is a complex colloidal mixture but is not classified as a typical lyophilic colloid.
Step 3: Conclusion.
The correct answer is (A) because milk is a lyophilic colloid.

Step 1: Understanding the composition of milk.
Milk is an emulsion, where fat droplets are dispersed in water. This makes it a colloidal system. Step 2: Analysis of options.
(A) fat dispersed in water: This is the correct answer as milk consists of fat droplets suspended in water.
(B) water dispersed in fat: This is incorrect. The main phase in milk is water, with fat dispersed in it.
(C) water dispersed in oil: This describes an inverse emulsion, which is not the case for milk.
(D) fat dispersed in fat: This is incorrect as milk is not composed of fat dispersed in fat.
Step 3: Conclusion.
The correct answer is (A) because milk consists of fat dispersed in water.