51. The surface area of adsorbents can be measured by:
- a) Freundlich equation
- b) Langmuir equation
- c) BET equation
- d) Van’t Hoff equation
Answer: c) BET equation
Explanation: The BET (Brunauer, Emmett, and Teller) equation is used to calculate the surface area of adsorbents by studying multilayer adsorption.
52. Which of the following statements is correct regarding adsorption?
- a) Adsorption is always exothermic.
- b) Adsorption increases with increasing temperature.
- c) Adsorption decreases the entropy of the system.
- d) Adsorption increases the internal energy of the adsorbate.
Answer: c) Adsorption decreases the entropy of the system.
Explanation: Adsorption leads to a decrease in entropy because the molecules of the adsorbate are more ordered when adsorbed on the surface than when they are free in the gas phase.
53. The Freundlich adsorption isotherm fails at:
- a) Low pressure
- b) High pressure
- c) Low temperature
- d) High temperature
Answer: b) High pressure
Explanation: The Freundlich adsorption isotherm is empirical and works well at moderate pressures. However, at high pressure, it fails to explain the saturation of the adsorbent, as the amount of adsorption reaches a maximum.
54. Which of the following materials is commonly used for removing moisture from air?
- a) Activated charcoal
- b) Silica gel
- c) Alumina
- d) Fuller’s earth
Answer: b) Silica gel
Explanation: Silica gel is highly porous and has a large surface area, making it an excellent desiccant for removing moisture from air.
55. Which of the following is not a characteristic of physical adsorption?
- a) It occurs at low temperatures.
- b) It forms a multilayer of adsorbate.
- c) It requires high activation energy.
- d) It involves Van der Waals forces.
Answer: c) It requires high activation energy.
Explanation: Physisorption occurs due to weak Van der Waals forces and does not require significant activation energy, unlike chemisorption.
56. Adsorption of gases on charcoal is maximum at:
- a) Low temperature and high pressure
- b) Low temperature and low pressure
- c) High temperature and high pressure
- d) High temperature and low pressure
Answer: a) Low temperature and high pressure
Explanation: Adsorption of gases on solids, such as charcoal, is favored at low temperatures (since adsorption is exothermic) and high pressures (since more gas molecules are available for adsorption).
57. The Langmuir adsorption isotherm applies to:
- a) Both monolayer and multilayer adsorption
- b) Only monolayer adsorption
- c) Chemisorption only
- d) Physisorption only
Answer: b) Only monolayer adsorption
Explanation: The Langmuir adsorption isotherm describes the adsorption of a single layer of molecules (monolayer) on the surface of an adsorbent.
58. In chemisorption, the adsorbed molecules are held on the surface of the solid by:
- a) Physical forces
- b) Covalent or ionic bonds
- c) Weak Van der Waals forces
- d) Gravitational forces
Answer: b) Covalent or ionic bonds
Explanation: In chemisorption, the adsorbate molecules are held on the surface of the adsorbent by strong chemical bonds, such as covalent or ionic bonds.
59. What type of adsorption is favored by an increase in pressure at constant temperature?
- a) Chemisorption
- b) Physisorption
- c) Both chemisorption and physisorption
- d) Adsorption is independent of pressure
Answer: b) Physisorption
Explanation: Physisorption is favored by an increase in pressure because more gas molecules are available for adsorption, and this type of adsorption depends significantly on pressure.
60. The adsorption of a gas on a solid surface is an exothermic process. This is because:
- a) The surface area increases during adsorption
- b) The randomness of the system increases
- c) Energy is released when gas molecules stick to the surface
- d) Energy is required to overcome the attraction between gas molecules
Answer: c) Energy is released when gas molecules stick to the surface
Explanation: Adsorption is an exothermic process because the gas molecules lose kinetic energy when they attach to the surface of the solid, releasing heat in the process.
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