Engineering Chemistry S Datta

COLLOIDS 289
SHORT QUESTIONS AND ANSWERS
Q. 1. Describe a colloidal system. What are the sizes of particles forming a
solution and a colloidal solution?
Ans. A colloidal system is a two-phase heterogeneous system in which one phase is
dispersed in a fine state of subdivision (from 1 to 50 mµ) in another medium termed the
continuous or dispersion medium.
The solute particles in true solution are of dimension 1 to 10 Å.
Particles of colloidal system have dimension in the range from 10 to 1000 Å.
Q. 2. What is the difference between sol and emulsion?
Ans. Sol is a colloidal solution of a solid dispersed in a liquid medium whereas emulsion
is a liquid dispersed in another immiscible liquid in the form of droplets.
Q. 3. Why are “Brownian movement” and “Tyndall effect” shown by colloidal
solutions but not the true solution?
Ans. Large particles of the colloid solution do not settle down and scatter the light
falling on the solution, whereas in true solution there are no such particles.
Q. 4. Write short notes on the following:
(a) Brownian movement
(b) Tyndall Effect
(c) Dialysis
(d) Gold number.
Ans. (a) See page 284
(b) See page 284
(c) See page 282
(d) See page 286.
Q. 5. Explain the action of gelatin as protective colloid.
Ans. Gelatin is a lyophilic colloid and when it is added to lyophobic sol, it forms a very
thin protective shell, surrounding each particle of the lyophobic colloid and protects the
penetration of oppositely charged ions, which neutralize the charge and precipitate the lyophobic
colloid.
Q. 6. Write notes on
(i) Electrophoresis
(ii) Peptization
(iii) Zeta potential
(iv) Protection of hydrophobic colloids.
Ans. (i) See page 285
(ii) See page 282
(iii) See page 287
(iv) See page 286.
Q. 7. Which of the following electrolytes will be most efficient for the
precipitation of As 2
S 3
sol and why?
(i) KCl
(ii) CaCl 2
(iii) AlCl 3
.