Surface Chemistry NCERT Intext Solutions

Que 1. Write any two characteristics of Chemisorption.
Ans 1. Two characteristics of Chemisorption-
(i) The bond formation between the solid(adsorbent) and the gas molecules is by chemical bonds.
(ii) It is highly specific in nature and also irreversible.

Que 2. Why does physisorption decrease with the increase of temperature?
Ans 2. Physical adsorption of a gas by a solid is generally reversible. Thus,
Solid + Gas  ↔ Gas / Solid + Heat
Since the adsorption process is exothermic, the physical adsorption occurs readily at low temperatures and decreases with increasing temperatures (Le Chatelier’s principle).

Que 3. Why are powdered substances more effective adsorbents than their crystalline forms?
Ans 3. Since adsorption is a surface phenomenon. So the extent of adsorption increases with an increase in the surface area of the adsorbent. Finely powdered substances have large, porous areas and act as good adsorbents.

Surface Chemistry NCERT Intext Solutions

Que 4. In Haber’s process, hydrogen is obtained by reacting methane with steam in presence of NiO as the catalyst. The process is known as steam reforming. Why is it necessary to remove CO when ammonia is obtained by Haber’s process?
Ans 4. CO acts as a poison for the catalyst used in the manufacture of NH3 by Haber’s process. Hence, it is necessary to remove it.

Que 5. Why the ester hydrolysis is slow in the beginning and becomes faster after some time?
Ans 5. The acid formed during the reaction provides hydrogen ions which act as catalysts for the reaction and it becomes faster.
Or
The acid produced in the reaction acts as an auto catalyst for the reaction.
RCOOR’ + H2O ↔ RCOOH + R’OH

Que 6. What is the role of desorption in the process of catalysis?
Ans 6. In the heterogeneous catalysis carried over the metal surface, adsorbed reactant species combine to form the products. They have to be desorbed from the surface so that more reactants may accommodate on the surface of the catalyst. Therefore, desorption has a specific role to play in the process of catalysis.

Surface Chemistry NCERT Intext Solutions

Que 7. What modification can you suggest in the Hardy Schulze law?
Ans 7. According to Hardy Schulze law, the coagulating ion has a charge opposite to that on the colloidal particles. Hence, the charge on colloidal particles is neutralized and coagulation occurs.
The modification suggested to this law is:
When oppositely charged sols are mixed in proper proportions to neutralize the charges of each other, coagulation of both the sol occurs.

Que 8. Why is it essential to wash the precipitate with water before estimating it quantitatively?
Ans 8.  Precipitates are generally formed in ionic reactions. Some ions of the reactants may be adsorbed or may stick on the surface of the particles of the precipitate. These can be removed by washing the precipitate repeatedly with water. In case these ions are not removed, they may introduce some error in weighing when the precipitate is estimated quantitatively.

 

SURFACE CHEMISTRY NOTES CLASS 12

Surface Chemistry NCERT Intext Solutions

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