Engineering Chemistry S Datta

290 ENGINEERING CHEMISTRY
Ans. As 2
S 3
sol is a negatively-charged sol and it can be precipitated by positively charged
ions of the added electrolyte. From the above three electrolytes, the positive ions obtained are
K + , Ca 2+ , and Al 3+ . Since Al 3+ possess highest positive valency, AlCl 3
will be the most efficient
electrolyte to ppt As 2
S 3
sol, as per Schulze-Hardy rule.
Q. 8. Explain how deltas are formed where rivers meet the sea.
Ans. See page 288.
Q. 9. Why is alum used to remove impurities from water?
Ans. See page 288.
Q. 10. Smoke coming out from the chimneys of different factories is led to
charged metallic plate—explain.
Ans. See page 288.
Q. 11. Mention some important applications of colloid chemistry to industries.
Ans. See page 288.
Q. 12. Differentiate between lyophilic and lyophobic solutions.
Ans. See page 279.
Q. 13. State Schulze-Hardy law.
Ans. See page 286.
Q. 14. What do you mean by isoelectric point?
Ans. The pH of the medium at which the dispersed colloidal particles are neutral and
hence do not migrate when an electric field is applied to the colloidal solution.
Q. 15. What happens when a sol is filtered through a filter paper?
Ans. If a sol is filtered through an ordinary filter paper, the colloidal particles will pass
through the pores of the filter paper since the pore-size of ordinary filter paper is larger than
the size of the colloidal particles.
EXERCISES
1. What are lyophilic and lyophobic sols?
2. Explain the following:
(a) Tyndall effect. (b) Brownian movement.
(c) Gold number
(d) Protective colloids.
3. Write a note on application of colloid chemistry in (i) pollution control and (ii) industries.
4. Explain: Electrophoresis and Electro-osmosis.
5. What are the different ways of protecting a colloidal solution from coagulation?
6. State Schulze-Hardy rule and explain with an example.
OBJECTIVE QUESTIONS
1. The sizes of the colloidal particles fall in the range
(a) 10 –2 to 10 –4 cm
(b) 10 –4 to 10 –7 cm
(c) 10 –7 to 10 –9 cm.
2. Light passing through a colloidal solution is
(a) Reflected
(b) Absorbed completely
(c) Scattered.