NCERT 12 Chemistry Surface chemistry Chapter 5 exercises 1

Q – 5.1. Why are substances like platinum and palladium often used for carrying out electrolysis of aqueous solution?
Ans. Platinum and palladium form inert electrodes, i.e., they are not attacked by the ions of the electrolyte or the products is an electrolysis. Hence, they are used as electrodes for carrying out the electrolysis.
Q – 5.2. Why does Physisorption decrease with increase of temperature?
Ans. Physisorption is an exothermic:
Solid + Gas ⇌ Gas/Solid + Heat
(Adsorbent) (Adsorbate) (Gas adsorbed on solid)
According to le Chatelier’s principle, if we increase the temperature, equilibrium will shift in the backward direction, i.e, gas is released from the surface on which it is adsorbed.
Q – 5.3. Why are powdered substance more effective adsorbent than their crystalline forms?
Ans. Powdered substance have grater surface area as compared to their crystalline forms. Greater the surface area, greater is the adsorption.
Q – 5.4. Why is it necessary to remove CO when ammonia is obtained by Haber’s process?
Ans. CO acts as a poison for the catalyst used in the manufacture of ammonia by Haber’s process. Hence, it is necessary to remove it.
Q – 5.5. Why is the ester hydrolysis slow in the beginning and becomes faster some time?
Ans. The ester hydrolysis takes place as follows:
RCOOR’ + H2O ⇌ RCOOH + R’OH
Ester Water Acid Alcohol
The acid produced in the reaction acts as catalyst (auto catalyst) for the reaction. Hence, the reaction becomes faster after some time.
Q – 5.6. What is the role of desorption in the process of catalysis?
Ans. Desorption makes the surface of the solid catalyst free for fresh adsorption of the reactants on the surface.
Q – 5.7. What modification can you suggest in the Hardy Schulze law?
Ans. According to Hardy Schulze law, the coagulating ion has charge opposite to that on the colloidal particles. Hence, the charge on colloidal particles is neutralized and coagulation occurs. The law can be modified to include the following:
When oppositely charged sols are mixed in proper proportion to neutralize the charges of each other, coagulation of both the sols occurs.
Q – 5.8. Why is it essential to wash the precipitate with water before estimating it quantitatively?
Ans. Some amount of the electrolytes mixed to form the precipitate remains adsorbed on the surface of the particles of the precipitate. Hence, it is essential to wash the precipitate with water to remove the sticking electrolytes (or any other impurities) before estimating it quantitatively.
Updated: October 7, 2020 — 9:53 am

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