Surface Chemistry Test - 5

Silver sol in water is an example of lyophobic sols.

A sol is a colloidal suspension of very small solid particles in a continuous liquid medium. Sols are quite stable and show Tyndall effect. For example: blood, pigmented ink, cell fluids and paint.

(A) Activated charcoal is used in gas masks to absorb poisonous gases like CO, CH_4, etc.
So, (A) – (c).
(B) Solid foam is a gas dispersed in a solid. Pumice stone is a sold foam.
Thus, (B) – (d).
(C) Cetyltrimethylammonium bromide is a micelle system.
So, (C) – (a).
(D) Elastic gels absorb water molecules when placed in it with simultaneous swelling of gel body. This is known as imbibition.
Thus, (D) – (b).

In lyophobic sol, weak forces of interaction exist between colloidal particles and liquid. Hence, the particles of the dispersed phase are less solvated and option (1) is incorrect.
All the other statements about the lyophobic sols are true.
Lyophobic sols are less stable. Addition of even small quantities of electrolytes can cause the particles to precipitate.

The colloidal particles in lyophilic colloids are well solvated because of affinity between the colloidal particles and the medium. This contributes to the stability of the colloids.

The induced catalyst used in the oxidation of sodium arsenite is sodium sulphite.

In this type of colloid, the colloidal particles are aggregates of atoms or small molecules with molecular size less than one nanometre (1 nm). Gold sol consists of particles of various sizes which are clusters of several gold atoms. Similarly, sulphur sol consists of colloidal particles which are aggregates of S₈ molecules. The molecules in the aggregates are held together by van der Waals forces.

Peptization - Some freshly prepared precipitates, such as AgCl, Fe (OH)₃ and Al(OH)₃, can be converted into colloidal solutions by addition of small amount of suitable electrolyte. An electrolyte having an ion common with material to be dispersed is required for sol formation.

For example, the ferric hydroxide sol is obtained when small amount of ferric chloride solution is added. Similarly, Al(OH)₃ sol is obtained when small amount of hydrochloric acid is added to freshly precipitated Al(OH)₃.