Class 12 Chemistry Ch-Surface Chemistry (MCQ)

1. Which of the following process does not occur at the interface of phases?
(i) crystallisation
(ii) heterogenous catalysis
(iii) homogeneous catalysis
(iv) corrosion

Answer Answer: (iii) homogeneous catalysis
Explanation: In homogeneous catalysis, only, the reactant and product are in same phase and composition is uniform throughout.

2. At the equilibrium position in the process of adsorption _.
(i) ΔH > 0
(ii) ΔH = TΔS
(iii) ΔH > TΔS
(iv) ΔH < TΔS

Answer Answer: Ans. (ii) ΔH = TΔS
Explanation: At equilibrium ΔG=0
ΔG=ΔH-TΔS
Therefore, ΔH=TΔS

3. Which of the following interface cannot be obtained?
(i) liquid-liquid
(ii) solid-liquid
(iii) liquid-gas
(iv) gas-gas

Answer Answer: (iv) gas-gas
Explanation: Because gas-gas forms homogeneous composition.

4. The term ‘sorption’ stands for __.
(i) absorption
(ii) adsorption
(iii) both absorption and adsorption
(iv) desorption

Answer Answer: (iii) both absorption and adsorption
Explanation: When adsorption and absorption occur simultaneously it is known as sorption.

5. Extent of physisorption of a gas increases with _.
(i) increase in temperature.
(ii) decrease in temperature.
(iii) decrease in surface area of adsorbent.
(iv) decrease in strength of van der Waals forces.

Answer Answer: (ii) decrease in temperature.
Explanation: Since the adsorption (Solid+ Gas=Gas/Solid+ Heat) process is exothermic, the physical adsorption occurs readily at low temperature and decreases with increasing temperature as the equilibrium will shift in backward direction. (Le-Chatelier’s principle).

6. Extent of adsorption of adsorbate from solution phase increases with __.
(i) increase in amount of adsorbate in solution.
(ii) decrease in surface area of adsorbent.
(iii) increase in temperature of solution.
(iv) decrease in amount of adsorbate in solution.

Answer Answer: (i) increase in amount of adsorbate in solution.
Explanation: The extent of adsorption depends on the concentration of the solute in solution as the concentration of adsorbate increase interaction between adsorbate and adsorbent increases thus the extent of adsorption increases.

7. Which one of the following is not applicable to the phenomenon of adsorption?
(i) ΔH > 0
(ii) ΔG < 0
(iii) ΔS < 0
(iv) ΔH < 0

Answer Answer: (i) ΔH > 0
Explanation: Since adsorption is an exothermic process ΔH cannot be greater than zero.

8. Which of the following is not a favourable condition for physical adsorption?
(i) high pressure
(ii) negative ΔH
(iii) higher critical temperature of adsorbate
(iv) high temperature

Answer Answer: (iv) high temperature
Explanation: High temperature is not favourable for physical adsorption since it is an exothermic process.

9. Physical adsorption of a gaseous species may change to chemical adsorption with
__.
(i) decrease in temperature
(ii) increase in temperature
(iii) increase in surface area of adsorbent
(iv) decrease in surface area of adsorbent

Answer Answer: (ii) increase in temperature
Explanation: On increasing the temperature activation energy of the adsorbate molecule increases. Which can convert physical adsorption into chemisorptions.

10. In physisorption adsorbent does not show specificity for any particular gas because
__.
(i) involved van der Waals forces are universal.
(ii) gases involved behave like ideal gases.
(iii) enthalpy of adsorption is low.
(iv) it is a reversible process.

Answer Answer: (i) involved van der Waals forces are universal.

11. Which of the following is an example of absorption?
(i) Water on silica gel
(ii) Water on calcium chloride
(iii) Hydrogen on finely divided nickel
(iv) Oxygen on metal surface

Answer Answer: (ii) Water on calcium chloride
Explanation: Absorption implies that a substance is uniformly distributed, through the body of the solid or liquid.

12. On the basis of data given below predict which of the following gases shows least
adsorption on a definite amount of charcoal?

(i) CO2
(ii) SO
(iii) CH4
(iv) H2
Answer Answer: (iv) H2
Explanation: Lesser the value of critical temp of gases lesser will the force of attraction among molecules and least will be the adsorption.

13. In which of the following reactions heterogenous catalysis is involved?
(a) 2SO2(g) + O2(g)→2SO2(g)
(b) 2SO2(g)→2SO3(g)
(c) N2(g) + 3H2(g)→2NH3(g)
(d) CH3COOCH3(l) + H2O(l) HCI → CH3COOH(aq) + CH3OH(aq) 
(i) (b), (c)
(ii) (b), (c), (d)
(iii) (a), (b), (c)
(iv) (d)

Answer Answer: (i) (b), (c)
Explanation: When the reactant and catalyst are in different phase it is known as heterogeneous catalysis.

14. At high concentration of soap in water, soap behaves as __.
(i) molecular colloid
(ii) associated colloid
(iii) macromolecular colloid
(iv) lyophilic colloid

Answer Answer: (ii) associated colloid <br. Explanation: There are some substances which at low concentrations behave as normal strong electrolytes, but at higher concentrations exhibit colloidal behavior due to the formation of aggregates. The aggregated particles thus formed are called micelles. These are also known as associated colloids.

15. Which of the following will show Tyndall effect?
(i) Aqueous solution of soap below critical micelle concentration.
(ii) Aqueous solution of soap above critical micelle concentration.
(iii) Aqueous solution of sodium chloride.
(iv) Aqueous solution of sugar.

Answer Answer: (ii) Aqueous solution of soap above critical micelle concentration
Explanation: Tyndall effect is the optical property shown by the colloidal particle. Above critical micelle concentration, a solution of soap behave as associated colloid that is why it shows tyndall effect.

16. Method by which lyophobic sol can be protected.
(i) By addition of oppositely charged sol.
(ii) By addition of an electrolyte.
(iii) By addition of lyophilic sol.
(iv) By boiling.

Answer Answer: (iii) By addition of lyophilic sol.
Explanation: Lyophilic colloids have a unique property of protecting lyophobic colloids. When a lyophilic sol is added to the lyophobic sol, the lyophilic particles form a layer around lyophobic particles and thus protect the latter from electrolytes. Lyophilic colloids used for this purpose are called protective colloids.

17. Freshly prepared precipitate sometimes gets converted to colloidal solution by __.
(i) coagulation
(ii) electrolysis
(iii) diffusion
(iv) peptisation

Answer Answer: (iv) peptisation
Explanation: Peptisation is the process in which freshly prepared precipitate can be converted into colloidal solution.

18. Which of the following electrolytes will have maximum coagulating
valueforAgI/Ag+sol?

(i) Na2S
(ii) Na3PO4
(iii) Na2SO4
(iv) NaCl

Answer Answer: (ii) Na3PO4
Explanation: Higher the value of oppositely charge electrolyte faster will be the rate of coagulation.

19. A colloidal system having a solid substance as a dispersed phase and a liquid as a
dispersion medium is classified as __.
(i) solid sol
(ii) gel
(iii) emulsion
(iv) sol

Answer Answer: (iv) sol
Explanation: Solid + liquid= sol (here solid is the dispersed phase and liquid is the dispersion medium.)

20. The values of colligative properties of colloidal solution are of small order in
comparison to those shown by true solutions of same concentration because of
colloidal particles ______.
(i) exhibit enormous surface area.
(ii) remain suspended in the dispersion medium.
(iii) form lyophilic colloids.
(iv) are comparatively less in number.

Answer Answer: (iv) are comparatively less in number.
Explanation: Colloidal particles being bigger aggregates, the number of particles in a colloidal solution is comparatively small as compared to a true solution. Hence, the values of colligative properties (osmotic pressure, lowering in vapour pressure, depression in freezing point and elevation in boiling point) are of small order as compared to values shown by true solutions at same concentration.

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