CBSE Class 12 Chemistry Surface Chemistry Questions Answers

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FAQ - Chapter 5 SURFACE CHEMISTRY

1. Bleeding caused by a nick from a razor during shaving can be stopped by rubbing with alum. Why?

Ans:- Blood is a negatively charged colloidal solution. When alum is rubbed the positively charged Al³+ ions from alum neutralizes the charge on the particles and makes it coagulate to form a clot.

2. In which of the following does adsorption take place and why?

(i) Silica gets placed in the atmosphere saturated with water.

(ii) Anhydrous CaCl₂ placed in the atmosphere saturated with water.

Ans:- In (i) because water vapor gets adsorbed on the surface of silica since it is a good adsorbent.

3. Action of soap is due to emulsification and micelle formation. Comment

Ans:- Soap molecules adsorb on to the dirt surface and try to emulsify it by forming micelles. Soap micelles thus make the insoluble dirt (greasy materials) into colloidal form such that it gets washed away by water.

4. What is the use of ZSM-5?

Ans:- It converts alcohols directly into gasoline (petrol) by dehydrating them to give a mixture of hydrocarbons.

5. Give one example for each (i) sol (ii) gel.

Ans:- (i) paints (ii) Butter or any other correct options.

6. What is collodion?

Ans:- It is a 4% solution of nitrocellulose in a mixture of alcohol and ether.

7. Can we form a colloid with two gaseous components? Comment.

Ans:- No. a gas mixed with another gas forms a homogeneous mixture which does not come under a colloidal system.

8. What are the physical states of the dispersion medium and dispersed phase in froth?

Ans:- In froth, the dispersed phase is a gas while dispersion medium is a liquid.

9. Write the equation for the preparation of colloidalsulphur ?

Ans:- SO₂ + 2H₂S →3S(sol) + 2H₂O

10. Why does physisorption decrease with increase of temperature?

Ans:- Adsorption is an exothermic phenomenon. The increase in temperature will favour the reverse process i.e. desorption according to Le Chatlier’s principle. Therefore physisorption decreases with increase in temperature.

11. What is CMC (Critical Micelle Concentration)

Ans:- It is a particular concentration above which the particles aggregate to form micelles or associated colloids.

12. Why are powdered substances more effective adsorbents as compared to their crystalline forms?

Ans:- Powdered form has more surface area than crystalline form.

13. Why is it necessary to remove CO when ammonia is obtained by Haber’s process?

Ans:- In Haber’s process iron is used as catalyst .If CO is present, it acts as catalytic poison.

14. What is electrophoresis due to?

Ans:- It is due to existence of positive or negative charge on colloidal particles.

15. Mention two ways by which lyophilic colloids can be coagulated. (C.B.S.E-2008)

Ans:- 1) By adding en electrolyte. 2) By adding a suitable solvent.

16. What is Kraft temperature? (C.B.S.E Foreign 2004)

Ans:- It is the temperature above which the formation of micelle takes place.

17. What is Brownian movement due to? (C.B.S.E -1999)

Ans:- It is due to unbalance bombardment of the colloidal particles by the molecules of dispersion medium.

18. Name two industrial processes in which heterogeneous catalysts are employed.(C.B.S.E-2008)

Ans:- (i).Manufacture of ammonia by Haber’s process. (ii) Manufacture of sulphuric acid by contact process.

19. What is an emulsion? (C.B.S.E Foreign 2009)

Ans:- Emulsion is a colloidal solution of two immiscible liquids of which one is the dispersion medium and the other is dispersed phase.

20. What is Zeta potential?

Ans:- The potential difference between the fixed layer and diffused layer of opposite charges around the colloidal particles.

21. What are the physical states of dispersed phase and dispersion medium of froth?

Ans:- Dispersed phase is gas, dispersion medium is liquid.

22. What is the cause of Brownian movement among colloidal particles?

Ans:- Due to collision between particles

23. Arrange the solutions: True solution, colloidal solution, suspension in decreasing order of their particles size?

Ans:– Suspension > colloidal > true solution

24. Give an example of micelles system?

Ans:- Sodium stearate (C₁₇ H₃₅ COO- Na+) 

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