Assertion Reason MCQs and Solved Questions Surface Chemistry

Assertion Reason MCQs and Solved Questions Surface Chemistry

Que 1. What is the sign of ΔH and ΔS for the adsorption of bromine on charcoal?
Ans 1.  Both ΔH and ΔS are negative.

Que 2. Why are substances like platinum and palladium often used for carrying out electrolysis of aqueous solutions?
Ans 2. Platinum and palladium are inert materials & are not attacked by the ions of the electrolyte or the products of electrolysis therefore used as electrodes for carrying out the electrolysis.

Que 3. Why does physisorption decrease with the increase in temperature?
Ans 3. Physisorption is an exothermic process i.e, heat is produced in the process.
Solid (adsorbent) + gas (adsorbate) ↔ gas/solid (gas adsorbed on solid) + heat
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 adsorbed surface.

Que 4. 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 in the manufacture of ammonia by Haber’s process.

Que 5. What are the physical states of the dispersed phase and dispersion medium of froth?
Ans 5. The dispersed phase is gas, dispersion medium is liquid.

Que 6. What is shape-selective catalysis?
Ans 6. It is the catalytic reaction that depends upon the pore structure of the catalyst and size of the reactant and product molecules.

Que 7. Why lyophilic colloids are more stable than lyophobic colloids?
Ans 7.  Due to (i) solvation (ii) charge on the colloidal particles.

Que 8. What is the cause of the Brownian movement among colloidal particles? 
Ans 8. Due to unequal collision between particles of the dispersed phase and the dispersion medium.

Que 9. Write the main reason for the stability of colloidal sols. 
Ans 9. Brownian movement/charge on colloidal particles.

Que 10. Give an example of a micelle system? 
Ans 10. Sodium stearate (C17H35COONa+).

Que 11. Write down the example of positively charged sol?
Ans 11. Ferric hydroxide sol.

A statement of assertion is followed by a statement of reason. Mark the correct choice from the options given below:
(a) Both assertion and reason are true and the reason is the correct explanation of assertion.
(b) Both assertion and reason are true but the reason is not the correct explanation of assertion.
(c) Assertion is true but the reason is false.
(d) Both assertion and reason are false.

Que 12. Assertion: A colloidal sol scatters light but a true solution does not.
Reason: The particles in a colloidal sol move slowly than in a true solution.
Ans 12. b

Que 13. Assertion: Activation energy for both the forward and backward reactions is lowered to the same extent by a catalyst.
Reason: A reaction cannot become fast by itself unless a catalyst is added.
Ans 13. c

Que 14. Assertion: Hydrolysis of the ester is an example of autocatalytic reaction.
Reason: A catalyst speeds up the process without participating in the mechanism.
Ans 14. c

Que 15. Assertion: Hydrated ferric oxide can be easily coagulated by sodium phosphate in comparison to KCl.
Reason: Phosphate ions have a higher negative charge than chloride ions. Hence, they are more effective for coagulation.
Ans 15. a

Que 16. Assertion: During the preparation of ice – cream, gelatin is added in it.
Reason: Ice -creams are emulsions that get stabilized by gelatin as it acts as an emulsifying agent.
Ans 16. a

Que 17. Which phenomenon is responsible for the formation of a delta?
Ans 17. Coagulation

Que 18. Name a cheap material useful for causing artificial rain?
Ans 18. Electrified sand

Que 19. Explain what is observed
(i) When a beam of light is passed through a colloidal soln.
(ii) Electric current is passed through a colloidal soln.
Ans 19. (i) Scattering of light by the colloidal particles takes place and the path of light becomes visible. This is known as the Tyndall effect.
(ii) On passing an electric current, colloidal particles move towards the oppositely charged electrodes where they lose their charge and get coagulated. This process is called electrophoresis.

Que 20. Explain:
(ii) Electrophoresis (ii) Coagulation
Ans 20. (i) The phenomenon involving the migration(movement) of colloidal particles under the influence of the electric field towards the oppositely charged electrode
(ii) The process of conversion of sol into precipitate, usually done by addition of suitable electrolytes. If the coagulated particles float on the surface of the dispersion medium, the coagulation is known as flocculation.

Que 21. What are micelles? Give an example of a micellar system.
Ans 21. Micelles are produced by the aggregation of a large number of ions in concentrated sol. Aggregated particles are known as micelles also known as associated soap, synthetic detergents.

Que 22. (i) Why is ferric chloride preferred over potassium chloride in the case of a cut leading to bleeding?
(ii) Why is desorption important for a substance to act as a good catalyst?
Ans 22. (i) Blood is a +vely charged colloid. One molecule of ferric chloride produces 3 –ve chloride ions while one molecule of potassium chloride produces one –ve chloride ion. Greater the –ve charge, the faster the coagulation.
(ii) After the reaction is over between the adsorbed reactants, the process of desorption must take place to remove the product molecules and create space for other reactant molecules to adsorb on the catalyst surface

Assertion Reason MCQs and Solved Questions Surface Chemistry

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