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12th Standard CBSE Chemistry Surface Chemistry Model Questions Paper

Published on: 31/07/2019

Surface Chemistry

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Std: 12th Standard CBSE - Chemistry

chapter: - Model Question paper

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Questions:

1 Marks

4 x 1 = 4

What is meant by critical micelle concentration?

Define the term 'Tyndall effect'.

What is meant by chemisorption?

What is meant by 'shape-selective catalysis' of reactions?

Generic 2

4 x 2 = 8

Draw a plot of variation in quantity of gas adsorbed \(\left( \frac { x }{ m } \right) \) with the pressure of the gas. Also plot the graph between log \(\frac { x }{ m } \) vs log p at constant temperature. What is slope of this line?

Which of two He and Ne, gets adsorbed on the surface of charcoal more readily, and why?

Describe a chemical method each for the preparation of the sols of sulphur and platinum in water.

(a) What happens when a freshly precipitated Fe(OH)₃ is shaken with water containing a small quantity of FeCl₃?
(b) Why is finely divided substance more effective as an adsorbent?

Generic 3

2 x 3 = 6

(a) Which will adsorb more gas, a lump of charcoal or its powder and why?
(b) Describe the preparation of the following colloidal solutions. Name the method used in each case:
(i) Silver sol
(ii) Sulphur sol

10.

(a) What are the two types of emulsions and how do they differ from one another? Give one example of each.
(b) Which one of the following electrolytes is most effective for the coagulation of Fe(OH)₃ sol and why?
NaCl, Na₂SO₄ , Na₃ PO₄

Multiple Choice Question

5 x 1 = 5

11.

Which of the following relation is correct ?
(i) x/m = constant at high pressure
(ii) x/m = constant xp^1/n (at intermediate pressure)
(iii) x/m = constant xpⁿ (at lower pressure)

(a)

all are correct

(b)

all are wrong

(c)

(i) and (ii) are correct

(d)

(iii) is correct

12.

The correct ascending order of adsorption of the following gases on the same mass of charcoal at the same mass of charcoal at the same temperature and pressure is

(a)

CH₄22

(b)

H₂42

(c)

SO₂42

(d)

H₂24

(e)

CH₄22

13.

Which of the following electrolytes will be most effective in the coagulation of gold sol?

(a)

NaNO₃

(b)

K₄ [Fe(CN)₆]

(c)

Na₃PO₄

(d)

MgCl₂

14.

Which one of the following forms an intrinsic colloid?

(a)

Sulphur

(b)

As₂S₃

(c)

Fe(OH)₃

(d)

Egg albumin

15.

Which of the following is true in respect of adsorption?

(a)

\(\triangle G<0,\triangle S>0,\triangle H<0\)

(b)

\(\triangle G<0,\triangle S<0,\triangle H<0\)

(c)

\(\triangle G>0,\triangle S>0,\triangle H<0\)

(d)

\(\triangle G<0,\triangle S<0,\triangle H>0\)

Fill up / 1 Marks

2 x 1 = 2

16.

Adsorption of N₂ gas on iron at 83 K is........where as at 773 K, it is.....................(fill in the type of adsorption).

17.

Increasing the adsorbing power of an adsorbent by subdividing it is called...............of the solid adsorbent.

Generic 5

2 x 5 = 10

18.

Radha and Meera are fast friends. They both study in class XII.Radha is a student of science while Meera follows commerce stream. One day, when they were playing, Radha got hurt and started bleeding. Meera took her to house and applied some alum on the cut. The bleeding stopped immediately.
(i)Why bleeding stopped when some alum is applied on the cut?
(ii) What are the values associated with Meera's decision to take Radha to her house and apply alum on her cut?

19.

20% of surface sites are occupied by N₂ molecules. The density of surface sites is \(6.023\times { 10 }^{ 14 }\) cm^-2 and total surface area is 1000 cm² . The catalyst is heated to 300 K while N₂ is completely disorbed into a pressure of 0.001 atm and volume 2.46 cm³. Find the active sites occupied by each N₂ molecule.

Match the following

5 x 1 = 5

20.

Butter

21.

Electrophoresis

22.

Emulsification

23.

Liquid in liquid

24.

Liquid in solid

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Answers Key:

1 Marks

4 x 1 = 4

()
The micelle may be defined as the aggregrated particles formed by associated colloids in solution. The formation of micelle takes place above certain concentration called critical micelle concentration (CMC).

()
When light passes through a colloidal solution, its path becomes clearly visible due to scattering of light by colloidal particles. This is called 'Tyndall effect'.

()
chemisorption: If the forces holding the adsorbate are as strong as in chemical bonds, the adsorption process is known as chemical adsorption or chemisorption.

()
shape-selective catalysis: The catalysis which depends upon the pore structure of the catalyst and molecular size of reactant and product molecules is called shape-selective catalysis, e.g. Zeolites are shape-selective catalysis due to their honey- comb structure. ZSM-5 (Zeolite Sieve of Molecular porosity is used to convert methanol into gasoline (petrol).

Generic 2

4 x 2 = 8

Ne will get adsorbed to more extent because it has large surface area, therefore, more van der Waals' forces of attraction, easily liquifiable as compared to He. It has higher critical temperature.

Sulfur sol can be prepared by oxidation of with the help\({ H }_{ 2 }S\) of Conc. \({ HNO }_{ 3 }\)
\({ H }_{ 2 }S\overset { [O] }{ \underset { { HNO }_{ 3 } }{ \rightarrow } } { H }_{ 2 }O+S\ \ { HNO }_{ 3 }\)
Bredig's Arc Method: Platinum (Pt) sol can be prepared by Bredig's arc method. Two Pt metal electrodes are taken through which high voltage is passed so that metal gets vaporized. When vapors are condensed, a colloidal solution of Pt in water is obtained.

(a) Colloidal solution of Fe(OH)₃ is formed. FeCl₃ acts as peptizing agent.
(b) It is due to greater surface area and it has more active sites. Therefore, extent of adsorption is more.

Generic 3

2 x 3 = 6

(a) The charcoal powder will adsorb more gas because it has more surface area.
(b) (i) Bredig's Arc method: Take silver electrodes in form of electric arc in water and pass high voltage through it. A lot of heat will be generated which will vaporize silver metal into vapors which on condensing form silver sol.
(ii) Oxidation: Pass H2S gas through an aqueous solution of nitric acid. A colloidal solution of sulfur will be obtained.
\({ H }_{ 2 }S+[O]\xrightarrow [ Conc.H{ NO }_{ 3 } ]{ } { H }_{ 2 }O+S\)

10.

(a) (i) Oil in water: When oil is dispersed in water, it is called oil in water, e.g. milk.
(ii) Water in oil: When water is dispersed in oil, it is called water in oil, e.g. butter in a liquid state.
(b) Fe(OH)3 is a positively charged colloid, therefore, Na3 P04 will be most effective for coagulation. It is because PO!- ions are negatively charged and have the highest charge among these electrolytes.

Multiple Choice Question

5 x 1 = 5

11.

12.

(b)
H₂42

13.

(d)
MgCl₂

14.

(d)
Egg albumin

15.

(b)
\(\triangle G<0,\triangle S<0,\triangle H<0\)

Fill up / 1 Marks

2 x 1 = 2

16.

()
physisorption, chemisorption.

17.

()
activation

Generic 5

2 x 5 = 10

18.

(i) Blood is a colloidal solution of albuminoid substance. The styptic action (blood stopping action) of alum is due to coagulation of blood forming a clot which stops further bleeding.
(ii) Values associated with Meera's decision are:
(a) Friendship
(b) Keen observation
(c) Applying knowledge of chemistry to daily life
(d) Responsibility
(e) Love and care.

19.

\(\frac { No.of\quad sites\quad occupied }{ No.of\quad { N }_{ 2 }\quad molecules } =\frac { 1.2046\times { 10 }^{ 17 } }{ 6.023\times { 10 }^{ 16 } } =2\)

Match the following

5 x 1 = 5

20.