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Chapter 5- Surface Chemistry Interview Questions Answers

Question 1 :

Write any two characteristics ofChemisorption.

Answer 1 :

1. Chemisorptionis highly specific in nature. It occurs only if there is a possibility ofchemical bonding between the adsorbent and the adsorbate.

2. Like physisorption, chemisorption also increases with anincrease in the surface area of the adsorbent.

Question 2 :

Why does physisorption decreasewith the increase of temperature?

Answer 2 :

Physisorption is exothermic innature. Therefore, in accordance with Le-Chateliere’s principle, it decreaseswith an increase in temperature. This means that physisorption occurs morereadily at a lower temperature.

Question 3 :

Why are powdered substances moreeffective adsorbents than their crystalline forms?

Answer 3 :

Powdered substances are moreeffective adsorbents than their crystalline forms because when a substance ispowdered, its surface area increases and physisorption is directly proportionalto the surface area of the adsorbent.

Question 4 :

Why is it necessary to remove COwhen ammonia is obtained by Haber’s process?

Answer 4 :

It is important to remove CO inthe synthesis of ammonia as CO adversely affects the activity of the ironcatalyst, used in Haber’s process.

Question 5 :

Why is the ester hydrolysis slowin the beginning and becomes faster after sometime?

Answer 5 :

Ester hydrolysis can berepresented as:

The acid produced in the reactionacts as a catalyst and makes the reaction faster. Substances that act ascatalysts in the same reaction in which they are obtained as products are knownas autocatalysts.

Question 6 :

What is the role of desorption inthe process of catalysis?

Answer 6 :

The role of desorption in theprocess of catalysis is to make the surface of the solid catalyst free for thefresh adsorption of the reactants on the surface.

Question 7 :

What modification can you suggestin the Hardy-Schulze law?

Answer 7 :

Hardy-Schulze law states that‘the greater the valence of the flocculating ion added, the greater is itspower to cause precipitation.’

Thislaw takes into consideration only the charge carried by an ion, not its size.The smaller the size of an ion, the more will be its polarising power. Thus,Hardy-Schulze law can be modified in terms of the polarising power of theflocculating ion. Thus, the modified Hardy-Schulze law can be stated as ‘thegreater the polarising power of the flocculating ion added, the greater is itspower to cause precipitation.’

Question 8 :

Distinguish between the meaningof the terms adsorption and absorption. Give one example of each.

Answer 8 :

Adsorption is a surface phenomenon of accumulation of molecules of a substance at the surface rather than in the bulk of a solid or liquid. The substance that gets adsorbed is called the ‘adsorbate’ and the substance on whose surface the adsorption takes place is called the ‘adsorbent’. Here, the concentration of the adsorbate on the surface of the adsorbent increases. In adsorption, the substance gets concentrated at the surface only. It does not penetrate through the surface to the bulk of the solid or liquid. For example, when we dip a chalk stick into an ink solution, only its surface becomes coloured. If we break the chalk stick, it will be found to be white from inside.

On the other hand, the process of absorption is a bulk phenomenon. In absorption, the substance gets uniformly distributed throughout the bulk of the solid or liquid.


Question 9 :

What is the difference betweenphysisorption and chemisorption?

Answer 9 :

Physisorption

Chemisorption

1.

In this type of adsorption, the adsorbate is attached to the surface of the adsorbent with weak van der Waal’s forces of attraction.

In this type of adsorption, strong chemical bonds are formed between the adsorbate and the surface of the adsorbent.

2.

No new compound is formed in the process.

New compounds are formed at the surface of the adsorbent.

3.

It is generally found to be reversible in nature.

It is usually irreversible in nature.

4.

Enthalpy of adsorption is low as weak van der Waal’s forces of attraction are involved. The values lie in the range of 20-40 kJ mol−1.

Enthalpy of adsorption is high as chemical bonds are formed. The values lie in the range of 40-400 kJ mol−1.

5.

It is favoured by low temperature conditions.

It is favoured by high temperature conditions.

6.

It is an example of multi-layer adsorption

It is an example of mono-layer adsorption.

Question 10 :

Give reason why a finely dividedsubstance is more effective as an adsorbent.

Answer 10 :

Adsorption is a surfacephenomenon. Therefore, adsorption is directly proportional to the surface area.A finely divided substance has a large surface area. Both physisorption andchemisorption increase with an increase in the surface area. Hence, a finelydivided substance behaves as a good adsorbent.


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