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Case Study Questions for Class 12 Chemistry Chapter 5 Surface Chemistry

There is Case Study Questions in class 12 Chemistry in session 2020-21. For the first time, the board has introduced the case study questions in the board exam. The first two questions in the board exam question paper will be based on Case Study and Assertion & Reason. The first question will have 5 MCQs out of which students will have to attempt any 4 questions. The second question will carry 5 Assertion & Reason type questions with the choice to attempt any four. Here are the questions based on case study.

Case Study Question 1:

Read the passage given below and answer the following questions:

Adsorption depends on the nature of the adsorbent. The rough solid surface has more number of pores and adsorb more number of gases than the smooth surface. Most common adsorbents are silica gel, activated charcoal. The extent of adsorption also depends on the surface area of solid. Specific surface area of an adsorbent is the surface area available for adsorption per gram of the adsorbent. The greater the surface area of the solid, the greater would be the adsoprtion. Charcoal is a more effective adsorbent than solid wood. Desorption is a process of removing an adsorbed substance from a surface on which it is absobed.

Physisorption is non-specific and any gas can be adsorbed. But the gases which are easily liquefiable (e.g., NH3, HCl, CO2) are adsorbed at a faster rate and to a large extent than the gases which are difficult to liquefy (e.g., H2, O2, N2). It denpends on the critical temperature. Higher the critical temperature of a gas, more easily liquefiable it is and more is the rate of adsorption. Chemisorption is specific in nature. Therefore, only those gases can be adsorbed which are capable of forming chemical bonds with the adsorbent.

The following questions are multiple choice questions. Choose the most appropriate answer:

(i) Select the correct statement regarding desoprtion.
(a) It is done by cooling or by increasing the pressure applied
(b) It is done by cooling or by increasing the pressure applied.
(c) It is done by heating or by reducing the pressure applied.
(d) It is done by heating or by increasing the pressure applied.

(ii) Which of the following statements regarding the physical adsorption of a gas on surface of solid is not correct?
(a) On increasing temperature, adsorption increases continuously
(b) Enthalpy changes are negative
(c) It is non-specific in nature
(d) It is reversible in nature.

(iii) At the same temperature and pressure, select the correct order of adsorption of the following gases on the same mass of charcoal.
(a) SO2 > CH4 > H2
(b) CH4 > SO2 > H2
(c) H2 > CH4 > SO2
(d) CH4 > H2 > SO2


Select the correct option among the following when adsorption of a gas on solid metal surface is spontaneous and exothermic.
(a) ΔS increases
(b) ΔS decreases
(c) ΔG increases
(d) ΔH decreases

(iv) Select the incorrect statement among the following.
(a) Physical adsorption occurs at a low temperature and chemisorption occurs at all temperature.
(b) In physisorption heat of adsorption is low while in chemisorption it is high.
(c) Chemisorption is irreversible and physisorption is reversible.
(d) Magnitude of chemisorption decreases with rise in temperature while physisorption increases with rise in temperature.

Answers (i) c
(ii) a
(iii) a or b
(iv) d

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