CBSE Class 12 Chemistry Surface Chemistry Worksheet Set C

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: Water vapour 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.

Important Questions for NCERT Class 12 Chemistry Surface Chemistry

Question. Preparation of Lyophobic sols by chemical method involves
(a) double decomposition
(b) oxidation & reduction
(c) hydrolysis
(d) all of these

Question. A colloidal solution is subjected to an electrical field. The particles move towards anode. The coagulation of same sol is studied using NaCl, BaCl₂ and AlCl₃ solutions. Their coagulating power should be
(a) NaCl > BaCl₂ > AlCl₃
(b) BaCl₂ > AlCl₃ > NaCl
(c) AlCl₃ > BaCl₂ > NaCl
(d) BaCl₂ > NaCl > AlCl₃

Question. Under the influence of an electric field, the particles in a sol migrate towards cathode. The coagulation of the same sol is studied using NaCl, Na₂SO₄ and Na₃PO₄ solutions. Their coagulating values will be in the order 
(a) NaCl > Na₂SO₄ > Na₃PO₄
(b) Na₂SO₄ > Na₃PO₄ > NaCl
(c) Na3PO₄ > Na₂SO₄ > NaCl
(d) Na₂SO₄ > NaCl > Na₃PO₄

Question. Gold numbers of protective colloids A, B, C and D are 0.50, 0.01, 0.10 and 0.005, respectively. The correct order of their protective powers is 
(a) D < A < C < B
(b) C < B < D < A
(c) A < C < B < D
(d) B < D < A < C

Question. The disease kala azar is caused by 
(a) colloidal antimony
(b) milk of magnesia
(c) argyrols
(d) colloidal gold

Question. Which one of the following impurities present in colloidal solution cannot be removed by electrodialysis? 
(a) Sodium chloride
(b) Potassium sulphate
(c) Urea
(d) Calcium chlorid

Question. The density of gold is 19 g/cm3. If 1.9 × 10^–4 g of gold is dispersed in one litre of water to give a sol having spherical gold particles of radius 10 nm, then the number of gold particles per mm³ of the sol will be 
(a) 1.9 × 10 ¹²
(b) 6.3 × 10 ¹⁴
(c) 6.3 × 10¹⁰
(d) 2.4 × 10⁶

Question. Which of the following electrolyte will have maximum flocculation value for Fe(OH)₃ sol?
(a) NaCl
(b) Na₂S 
(c) (NH₄)₃PO₄
(d) K₂SO₄

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