Here below some basic MCQ’s about “Adsorption” with answer explanation for exam practice. Let’s check one by one.
1. Which of the following statements about adsorption is true?
- a) Adsorption is an exothermic process.
- b) Adsorption increases with an increase in temperature.
- c) Adsorption is an endothermic process.
- d) Adsorption does not depend on the nature of adsorbent.
Answer: a) Adsorption is an exothermic process.
Explanation: Adsorption involves the accumulation of particles on the surface, and energy is released when this happens, making it an exothermic process. As the adsorbate molecules bind to the surface, they lose some of their energy in the form of heat.
2. Which of the following is an example of physical adsorption?
- a) Hydrogen on nickel
- b) Oxygen on charcoal
- c) Nitrogen on iron
- d) Chlorine on glass
Answer: b) Oxygen on charcoal
Explanation: Physical adsorption, or physisorption, involves weak Van der Waals forces between the adsorbate and adsorbent. Oxygen adsorption on charcoal is a common example of physisorption, where the interactions are weak and reversible.
3. The amount of gas adsorbed on a solid surface is generally affected by:
- a) Temperature
- b) Pressure of gas
- c) Nature of adsorbate and adsorbent
- d) All of the above
Answer: d) All of the above
Explanation: The extent of adsorption depends on multiple factors:
- Temperature: Adsorption typically decreases with an increase in temperature (Le Chatelier’s principle).
- Pressure: Adsorption increases with an increase in pressure.
- Nature: The nature of both the adsorbate and adsorbent (such as surface area and porosity) plays a significant role.
4. In chemisorption, which of the following is correct?
- a) Adsorption is rapid and reversible.
- b) Adsorption involves weak Van der Waals forces.
- c) Adsorption involves chemical bond formation.
- d) Adsorption decreases with pressure.
Answer: c) Adsorption involves chemical bond formation.
Explanation: Chemisorption involves the formation of chemical bonds between the adsorbate and the adsorbent. This is usually an irreversible process and depends on the nature of the substances involved. Chemisorption is stronger than physisorption.
5. Freundlich adsorption isotherm is expressed as:
- a) x/m=Kpn
- b) x/m=Kp1/n
- c) x/m=Kp
- d) x/m=Kp2
Answer: b) x/m=Kp1/n
Explanation: Freundlich adsorption isotherm is a mathematical relationship between the quantity of gas adsorbed by unit mass of the adsorbent (x/m) and the pressure of the gas (p). The constant K and exponent nn depend on the nature of the adsorbate and adsorbent.
6. Which of the following is NOT a characteristic of chemisorption?
- a) High activation energy
- b) Irreversible
- c) Forms a monolayer
- d) Occurs at low temperature
Answer: d) Occurs at low temperature
Explanation: Chemisorption typically occurs at higher temperatures because it involves the formation of chemical bonds, which requires activation energy. Physical adsorption (physisorption) occurs at lower temperatures and does not require significant activation energy.
7. Which of the following statements is true regarding the difference between physisorption and chemisorption?
- a) Physisorption involves chemical bonds, while chemisorption involves weak forces.
- b) Physisorption occurs at high temperatures, while chemisorption occurs at low temperatures.
- c) Physisorption occurs at low temperature, while chemisorption occurs at high temperature.
- d) Physisorption is irreversible, while chemisorption is reversible.
Answer: c) Physisorption occurs at low temperature, while chemisorption occurs at high temperature.
Explanation: Physisorption involves weak Van der Waals forces and typically occurs at low temperatures, while chemisorption requires higher temperatures due to the energy required to form chemical bonds between the adsorbate and the adsorbent.
8. In Langmuir adsorption isotherm, adsorption is assumed to occur:
- a) On a heterogeneous surface.
- b) On a multilayer surface.
- c) On a monolayer surface.
- d) Only in the presence of catalysts.
Answer: c) On a monolayer surface.
Explanation: Langmuir adsorption isotherm assumes that adsorption occurs on a homogeneous surface where each site can hold only one molecule, leading to the formation of a monolayer. It does not account for multilayer adsorption like the BET theory.
9. Which of the following gases would be adsorbed most easily on a solid surface?
- a) Helium
- b) Nitrogen
- c) Carbon dioxide
- d) Hydrogen
Answer: c) Carbon dioxide
Explanation: Gases with higher polarizability and larger molecular sizes are adsorbed more easily. Carbon dioxide is more easily adsorbed compared to nitrogen or helium because it is a larger, more polarizable molecule.
10. The heat of adsorption is highest for:
- a) Physisorption
- b) Chemisorption
- c) Both are equal
- d) Cannot be compared
Answer: b) Chemisorption
Explanation: Chemisorption involves the formation of chemical bonds, which results in higher heat of adsorption compared to physisorption, where the forces are weak Van der Waals interactions.
11. Which of the following is true for the adsorption of gases on a solid surface?
- a) The extent of adsorption increases at high temperature.
- b) The extent of adsorption decreases with an increase in surface area of the adsorbent.
- c) The extent of adsorption increases with a decrease in temperature.
- d) Adsorption occurs more easily on smooth surfaces.
Answer: c) The extent of adsorption increases with a decrease in temperature.
Explanation: Adsorption is an exothermic process, and according to Le Chatelier’s principle, lowering the temperature favors adsorption by shifting the equilibrium towards more adsorption.
12. Which of the following factors does NOT affect the rate of physisorption?
- a) Nature of adsorbent
- b) Temperature
- c) Pressure
- d) Bonding between adsorbate and adsorbent
Answer: d) Bonding between adsorbate and adsorbent
Explanation: Physisorption involves weak Van der Waals forces and does not require any bonding between the adsorbate and adsorbent. Chemisorption, on the other hand, involves chemical bonding.
13. Which of the following statements is true about adsorption?
- a) It is always irreversible.
- b) It involves the formation of a multilayer of molecules.
- c) It results in the increase of entropy of the system.
- d) It is spontaneous and results in a decrease of free energy.
Answer: d) It is spontaneous and results in a decrease of free energy.
Explanation: Adsorption is spontaneous, leading to a decrease in the system’s free energy (ΔG < 0), though the process reduces the entropy (ΔS < 0) since it involves the ordering of adsorbate molecules on the surface of the adsorbent.
14. The Langmuir adsorption isotherm assumes that:
- a) Adsorption is a reversible process.
- b) The surface is homogeneous.
- c) Multilayer adsorption occurs.
- d) There is a fixed number of adsorption sites.
Answer: b) The surface is homogeneous.
Explanation: The Langmuir adsorption isotherm assumes that the surface of the adsorbent is uniform (homogeneous) and that all adsorption sites are equivalent.
15. Freundlich adsorption isotherm applies to:
- a) Ideal gases
- b) Ideal liquids
- c) Both monolayer and multilayer adsorption
- d) Only monolayer adsorption
Answer: c) Both monolayer and multilayer adsorption
Explanation: Freundlich adsorption isotherm is empirical and can describe both monolayer and multilayer adsorption, depending on the adsorbent-adsorbate interaction.
16. At low pressure, adsorption of a gas on a solid follows which order?
- a) First order
- b) Zero order
- c) Second order
- d) Third order
Answer: a) First order
Explanation: At low pressures, the amount of gas adsorbed varies directly with the pressure, so adsorption follows first-order kinetics.
17. Which of the following is a characteristic of physisorption?
- a) It occurs at high temperatures.
- b) It requires a large amount of activation energy.
- c) It forms multiple layers of adsorbate on the surface.
- d) It is highly specific.
Answer: c) It forms multiple layers of adsorbate on the surface.
Explanation: Physisorption can lead to multilayer adsorption because the forces involved (Van der Waals forces) allow for weak attraction of more than one layer of molecules onto the surface of the adsorbent.
18. Chemisorption typically:
- a) Involves weak Van der Waals forces.
- b) Occurs at low temperatures.
- c) Forms multilayers of adsorbate.
- d) Requires activation energy.
Answer: d) Requires activation energy.
Explanation: Chemisorption involves the formation of strong chemical bonds between adsorbate and adsorbent, which requires activation energy, unlike physisorption.
19. The BET isotherm is primarily used to describe:
- a) Monolayer adsorption
- b) Multilayer adsorption
- c) Chemical adsorption
- d) Gaseous adsorption on metals
Answer: b) Multilayer adsorption
Explanation: The BET (Brunauer, Emmett, Teller) isotherm is an extension of the Langmuir model and describes multilayer adsorption, where the adsorbate forms multiple layers on the adsorbent surface.
20. Which of the following is NOT a correct assumption of the Langmuir adsorption isotherm?
- a) Adsorption sites are equivalent.
- b) Adsorption occurs uniformly over the surface.
- c) Multilayer adsorption occurs.
- d) Adsorption is restricted to a monolayer.
Answer: c) Multilayer adsorption occurs.
Explanation: Langmuir adsorption isotherm assumes adsorption occurs only in a single monolayer, not multilayer adsorption.
21. The extent of adsorption of gases on a solid increases with:
- a) Increase in temperature
- b) Decrease in surface area
- c) Increase in critical temperature of gas
- d) Decrease in pressure of gas
Answer: c) Increase in critical temperature of gas
Explanation: Gases with a higher critical temperature are more easily liquefied and exhibit greater adsorption, as they have stronger intermolecular forces.
22. Which of the following adsorption isotherms assumes multilayer adsorption?
- a) Freundlich
- b) Langmuir
- c) BET
- d) Temkin
Answer: c) BET
Explanation: The BET isotherm extends the Langmuir model to account for multilayer adsorption, making it suitable for studying adsorption on porous surfaces.
23. Which of the following substances is commonly used as an adsorbent in gas masks?
- a) Silica gel
- b) Activated charcoal
- c) Alumina
- d) Fuller’s earth
Answer: b) Activated charcoal
Explanation: Activated charcoal is used in gas masks due to its high surface area and ability to adsorb a wide range of gases and toxic substances.
24. In adsorption from solution, the amount adsorbed depends on:
- a) Temperature only
- b) Pressure only
- c) Concentration of solute
- d) The type of solvent used
Answer: c) Concentration of solute
Explanation: In adsorption from solution, the extent of adsorption is directly related to the concentration of the solute; the greater the concentration, the greater the adsorption.
25. The process of adsorption generally:
- a) Increases the surface energy of the adsorbent.
- b) Decreases the surface energy of the adsorbent.
- c) Has no effect on the surface energy of the adsorbent.
- d) Occurs with an increase in entropy.
Answer: b) Decreases the surface energy of the adsorbent.
Explanation: Adsorption decreases the surface energy of the adsorbent because the adsorbate molecules reduce the free energy of the surface by binding to it.
26. Which of the following is not a factor affecting adsorption of gases on solids?
- a) Nature of the gas
- b) Temperature
- c) Nature of the solid
- d) External magnetic field
Answer: d) External magnetic field
Explanation: The adsorption of gases on solids is primarily influenced by the nature of the gas, temperature, and the nature of the solid adsorbent. An external magnetic field does not typically affect adsorption unless the adsorbent or adsorbate is magnetic.
27. Adsorption isotherms are useful to describe:
- a) Variation of temperature with time
- b) Variation of pressure with temperature
- c) Variation of adsorption with temperature
- d) Variation of adsorption with pressure
Answer: d) Variation of adsorption with pressure
Explanation: Adsorption isotherms describe how the extent of adsorption varies with pressure at a constant temperature. They provide insight into the surface properties of the adsorbent.
28. What happens to adsorption if the surface area of the adsorbent is increased?
- a) Adsorption increases
- b) Adsorption decreases
- c) Adsorption remains constant
- d) Adsorption depends only on temperature
Answer: a) Adsorption increases
Explanation: Adsorption increases with an increase in surface area because more surface sites are available for adsorbate molecules to adhere to.
29. Which of the following is the main driving force for physical adsorption?
- a) Chemical bonding
- b) Van der Waals forces
- c) Hydrogen bonding
- d) Covalent bonding
Answer: b) Van der Waals forces
Explanation: Physisorption is driven by weak Van der Waals forces, which are short-range, attractive interactions between the adsorbate and the surface of the adsorbent.
30. Which of the following gases would be the least adsorbed on a solid surface at room temperature?
- a) Carbon dioxide
- b) Oxygen
- c) Hydrogen
- d) Nitrogen
Answer: c) Hydrogen
Explanation: Hydrogen has a very low critical temperature and small molecular size, making it less prone to adsorption compared to gases like CO₂ or O₂.
31. In the context of adsorption, the term “sorption” refers to:
- a) Only adsorption
- b) Only absorption
- c) Both adsorption and absorption
- d) Neither adsorption nor absorption
Answer: c) Both adsorption and absorption
Explanation: Sorption is a general term that refers to both adsorption (surface phenomenon) and absorption (bulk phenomenon).
32. Which statement is true for chemisorption as compared to physisorption?
- a) Chemisorption is non-specific.
- b) Chemisorption is reversible.
- c) Chemisorption requires activation energy.
- d) Chemisorption involves weak forces.
Answer: c) Chemisorption requires activation energy.
Explanation: Chemisorption involves the formation of chemical bonds, which typically require activation energy. This makes it different from physisorption, which involves weak Van der Waals forces and occurs at lower temperatures without significant energy input.
33. A decrease in temperature usually:
- a) Increases physisorption and decreases chemisorption.
- b) Increases chemisorption and decreases physisorption.
- c) Increases both physisorption and chemisorption.
- d) Decreases both physisorption and chemisorption.
Answer: a) Increases physisorption and decreases chemisorption.
Explanation: Physisorption increases at lower temperatures because it involves weak Van der Waals forces that are enhanced at lower kinetic energies. Chemisorption, on the other hand, often requires higher temperatures for bond formation and activation energy.
34. Activated charcoal is used to adsorb gases because:
- a) It is inexpensive
- b) It has a high surface area
- c) It is chemically reactive
- d) It is inert
Answer: b) It has a high surface area
Explanation: Activated charcoal has an extremely high surface area, allowing it to adsorb large amounts of gases and impurities, making it ideal for use in air purification and gas masks.
35. Adsorption of gases on solids can be increased by:
- a) Increasing temperature
- b) Increasing surface area of the solid
- c) Decreasing pressure
- d) Using smooth surfaces
Answer: b) Increasing surface area of the solid
Explanation: The greater the surface area of the adsorbent, the more sites are available for adsorption, hence increasing the extent of adsorption.
36. Which of the following is NOT true for physisorption?
- a) It forms a multilayer of adsorbate.
- b) It occurs at low temperatures.
- c) It is highly specific.
- d) It is reversible.
Answer: c) It is highly specific.
Explanation: Physisorption is not specific to any particular type of adsorbate and occurs through weak Van der Waals forces, making it a non-specific process.
37. Which of the following adsorption isotherms explains the formation of a monolayer of adsorbate?
- a) Langmuir isotherm
- b) Freundlich isotherm
- c) BET isotherm
- d) Temkin isotherm
Answer: a) Langmuir isotherm
Explanation: The Langmuir adsorption isotherm assumes the formation of a monolayer on the adsorbent surface and that all adsorption sites are equivalent.
38. For physical adsorption, the enthalpy change (ΔH) is generally:
- a) Highly positive
- b) Highly negative
- c) Slightly negative
- d) Zero
Answer: c) Slightly negative
Explanation: Physical adsorption (physisorption) releases a small amount of heat, making the enthalpy change slightly negative. The process is exothermic, but the energy released is not as large as in chemisorption.
39. The extent of adsorption of a gas on a solid is generally:
- a) Inversely proportional to pressure at constant temperature.
- b) Directly proportional to pressure at constant temperature.
- c) Independent of temperature.
- d) Independent of pressure.
Answer: b) Directly proportional to pressure at constant temperature.
Explanation: As pressure increases at constant temperature, more gas molecules collide with the solid surface, increasing the extent of adsorption. This is particularly true at low pressures.
40. Which of the following statements is correct for adsorption?
- a) Adsorption increases with an increase in temperature.
- b) Adsorption is an endothermic process.
- c) Adsorption increases with an increase in surface area.
- d) Adsorption is independent of the adsorbate.
Answer: c) Adsorption increases with an increase in surface area.
Explanation: A larger surface area provides more adsorption sites, leading to greater adsorption of gases or solutes.
41. Adsorption from solutions depends on:
- a) Solubility of solute
- b) Concentration of solute
- c) Temperature of solution
- d) All of the above
Answer: d) All of the above
Explanation: Adsorption from a solution is affected by the solubility of the solute, its concentration, and the temperature of the solution. These factors influence how much solute is adsorbed by the solid adsorbent.
42. The adsorption of gases on the surface of a solid is due to:
- a) Strong attractive forces between gas molecules
- b) Weak attractive forces between gas and solid surface
- c) Repulsive forces between gas molecules
- d) High kinetic energy of gas molecules
Answer: b) Weak attractive forces between gas and solid surface
Explanation: In physisorption, weak Van der Waals forces are responsible for the adsorption of gas molecules on the surface of a solid.
43. Which of the following isotherms is most suitable to explain adsorption at very high pressures?
- a) Langmuir isotherm
- b) Freundlich isotherm
- c) BET isotherm
- d) Temkin isotherm
Answer: a) Langmuir isotherm
Explanation: The Langmuir isotherm describes adsorption that forms a monolayer on the surface of an adsorbent. At high pressure, all available adsorption sites are occupied, and the extent of adsorption becomes independent of pressure.
44. The adsorption of gases on solids can be increased by:
- a) Decreasing surface area of the adsorbent
- b) Decreasing temperature
- c) Increasing temperature
- d) Decreasing pressure
Answer: b) Decreasing temperature
Explanation: Adsorption is an exothermic process. Lowering the temperature favors adsorption by shifting the equilibrium towards more adsorption, according to Le Chatelier’s principle.
45. Adsorption of a gas on a solid is favorable when:
- a) ΔH is positive and ΔS is negative
- b) ΔH is negative and ΔS is positive
- c) ΔH is negative and ΔS is negative
- d) ΔH is positive and ΔS is positive
Answer: c) ΔH is negative and ΔS is negative
Explanation: Adsorption involves a decrease in enthalpy (ΔH is negative) because the process is exothermic. It also involves a decrease in entropy (ΔS is negative) because the adsorbate molecules are localized on the surface.
46. The Freundlich adsorption isotherm is expressed as x/m=kP1/nx/m=kP1/n. Which statement is true about this equation?
- a) It applies only at high pressures.
- b) n=1n=1 corresponds to chemisorption.
- c) It explains adsorption on a homogeneous surface.
- d) It is an empirical equation that applies to both monolayer and multilayer adsorption.
Answer: d) It is an empirical equation that applies to both monolayer and multilayer adsorption.
Explanation: The Freundlich adsorption isotherm is an empirical equation used to describe adsorption on heterogeneous surfaces and can apply to both monolayer and multilayer adsorption.
47. Which one of the following does NOT describe chemisorption?
- a) Formation of a monolayer
- b) High specificity
- c) Reversible adsorption
- d) Involves chemical bonding
Answer: c) Reversible adsorption
Explanation: Chemisorption involves the formation of strong chemical bonds between the adsorbate and the adsorbent, making the process irreversible in most cases.
48. The heat of adsorption in physisorption is generally:
- a) Equal to the heat of condensation
- b) Much higher than the heat of condensation
- c) Lower than the heat of condensation
- d) Unrelated to the heat of condensation
Answer: a) Equal to the heat of condensation
Explanation: In physisorption, the heat of adsorption is comparable to the heat of condensation because both processes involve weak Van der Waals forces.
49. Which of the following types of adsorption is involved when hydrogen is adsorbed on a nickel surface?
- a) Physisorption
- b) Chemisorption
- c) Endothermic adsorption
- d) Non-specific adsorption
Answer: b) Chemisorption
Explanation: Hydrogen adsorption on a nickel surface involves chemisorption, where strong chemical bonds are formed between hydrogen and the nickel surface.
50. Which of the following is true for chemisorption compared to physisorption?
- a) Chemisorption is faster than physisorption.
- b) Chemisorption is weaker than physisorption.
- c) Chemisorption occurs at higher temperatures.
- d) Chemisorption is non-specific.
Answer: c) Chemisorption occurs at higher temperatures.
Explanation: Chemisorption typically occurs at higher temperatures because it involves the activation energy needed to form chemical bonds between the adsorbent and adsorbate.
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.
61. What is the effect of temperature on the adsorption of gases on solids?
- a) Adsorption increases with an increase in temperature.
- b) Adsorption decreases with an increase in temperature.
- c) Adsorption remains constant with an increase in temperature.
- d) Adsorption first increases and then decreases with an increase in temperature.
Answer: b) Adsorption decreases with an increase in temperature
Explanation: Adsorption is an exothermic process, so according to Le Chatelier’s principle, increasing the temperature shifts the equilibrium towards desorption, reducing the extent of adsorption.
62. Which of the following isotherms is associated with multilayer adsorption?
- a) Langmuir isotherm
- b) Freundlich isotherm
- c) BET isotherm
- d) Temkin isotherm
Answer: c) BET isotherm
Explanation: The BET isotherm explains the adsorption of gases on solids and can account for the formation of multilayers of adsorbate molecules.
63. Which of the following characteristics is incorrect for physical adsorption?
- a) It is reversible.
- b) It forms a multilayer of adsorbate.
- c) It occurs at high temperatures.
- d) It involves weak Van der Waals forces.
Answer: c) It occurs at high temperatures
Explanation: Physical adsorption generally occurs at low temperatures because the weak Van der Waals forces holding the adsorbate to the surface are not strong enough to overcome increased thermal energy at high temperatures.
64. Which of the following is true for both physisorption and chemisorption?
- a) Both are endothermic processes.
- b) Both involve Van der Waals forces.
- c) Both increase with decreasing temperature.
- d) Both involve the attraction of molecules to a solid surface.
Answer: d) Both involve the attraction of molecules to a solid surface
Explanation: Both physisorption and chemisorption involve the attraction of adsorbate molecules to the surface of a solid, though the nature of the forces differs (weak Van der Waals forces in physisorption and stronger chemical bonds in chemisorption).
65. In which of the following is the interaction between adsorbent and adsorbate the strongest?
- a) Physisorption of CO₂ on charcoal
- b) Chemisorption of H₂ on nickel
- c) Physisorption of N₂ on silica gel
- d) Adsorption of water on silica gel
Answer: b) Chemisorption of H₂ on nickel
Explanation: Chemisorption involves strong chemical bonds between the adsorbent and the adsorbate, making the interaction stronger than in physisorption, which only involves weak Van der Waals forces.
66. Which of the following adsorption processes involves an increase in entropy?
- a) Chemisorption
- b) Physisorption
- c) Adsorption of gases on a solid
- d) Adsorption of solutes from solution
Answer: d) Adsorption of solutes from solution
Explanation: When a solute is adsorbed from a solution onto a solid surface, the solvent molecules are freed from the solvation shell of the solute, leading to an increase in the entropy of the system.
67. Which of the following factors does not affect the adsorption of gases on solids?
- a) Temperature
- b) Pressure
- c) Nature of adsorbent
- d) Volume of the gas
Answer: d) Volume of the gas
Explanation: The extent of adsorption depends on the temperature, pressure, and nature of the adsorbent, but not directly on the volume of the gas.
68. Which type of adsorption is likely to occur when a gas is adsorbed on a non-reactive solid surface like charcoal at low temperature?
- a) Chemisorption
- b) Physisorption
- c) Both physisorption and chemisorption
- d) Neither physisorption nor chemisorption
Answer: b) Physisorption
Explanation: Physisorption occurs at low temperatures and involves weak Van der Waals forces, making it the likely type of adsorption when a gas is adsorbed on a non-reactive surface like charcoal.
69. Which one of the following does NOT apply to the adsorption process?
- a) It is spontaneous.
- b) It increases with increasing surface area.
- c) It increases with increasing temperature.
- d) It is exothermic.
Answer: c) It increases with increasing temperature
Explanation: Adsorption is generally exothermic and decreases with increasing temperature because high thermal energy discourages the adherence of adsorbate molecules to the surface.
70. The Langmuir adsorption isotherm is based on the assumption that:
- a) Adsorption occurs on a heterogeneous surface.
- b) Adsorption forms a multilayer of adsorbate.
- c) Adsorption occurs on specific homogeneous sites on the surface.
- d) Adsorption occurs at variable energies at different sites.
Answer: c) Adsorption occurs on specific homogeneous sites on the surface
Explanation: The Langmuir adsorption isotherm assumes a homogeneous surface with specific sites for adsorption, where only a monolayer is formed.
71. In the Freundlich adsorption isotherm, what does the value of 1/n1/n between 0 and 1 represent?
- a) The process is endothermic.
- b) Adsorption is favored at high pressure.
- c) The adsorption is physisorption.
- d) The adsorption intensity.
Answer: d) The adsorption intensity
Explanation: In the Freundlich adsorption isotherm, the value of 1/n1/n provides a measure of the adsorption intensity. When 1/n1/n is between 0 and 1, adsorption is favorable.
72. Which one of the following statements is incorrect for chemisorption?
- a) It is highly specific.
- b) It involves weak forces.
- c) It forms a monolayer.
- d) It is irreversible.
Answer: b) It involves weak forces
Explanation: Chemisorption involves the formation of strong chemical bonds between the adsorbate and the adsorbent, not weak forces like in physisorption.
73. Which of the following gases will be adsorbed to the greatest extent on activated charcoal at 25°C?
- a) Nitrogen
- b) Oxygen
- c) Carbon dioxide
- d) Hydrogen
Answer: c) Carbon dioxide
Explanation: Carbon dioxide is adsorbed more readily than other gases like nitrogen, oxygen, or hydrogen due to its higher polarizability and greater tendency to interact with the surface of the adsorbent.
74. Which statement is incorrect for adsorption?
- a) Adsorption is an exothermic process.
- b) The extent of adsorption increases with increasing temperature for physisorption.
- c) The extent of adsorption increases with increasing pressure.
- d) Adsorption is spontaneous.
Answer: b) The extent of adsorption increases with increasing temperature for physisorption
Explanation: Physisorption decreases with increasing temperature because higher thermal energy counteracts the weak Van der Waals forces responsible for adsorption.
75. In the context of adsorption, what is an “adsorbate”?
- a) The substance onto which adsorption occurs
- b) The substance being adsorbed
- c) A catalyst used in adsorption
- d) The surface area of the adsorbent
Answer: b) The substance being adsorbed
Explanation: The adsorbate is the substance that is being adsorbed onto the surface of the adsorbent during the adsorption process.
76. The BET equation for adsorption is primarily used to determine:
- a) The volume of adsorbed gas
- b) The specific surface area of a solid
- c) The temperature of adsorption
- d) The thickness of the adsorbed layer
Answer: b) The specific surface area of a solid
Explanation: The BET equation is used to calculate the specific surface area of porous materials by analyzing multilayer adsorption data.
77. Which of the following is correct for the enthalpy change during chemisorption?
- a) It is positive.
- b) It is highly positive.
- c) It is negative.
- d) It is zero.
Answer: c) It is negative
Explanation: Chemisorption is an exothermic process, meaning the enthalpy change (ΔH) is negative as energy is released when chemical bonds are formed between the adsorbate and the adsorbent.
78. Which of the following can be used as an adsorbent for the removal of moisture from air?
- a) Activated charcoal
- b) Silica gel
- c) Fuller’s earth
- d) Graphite
Answer: b) Silica gel
Explanation: Silica gel is a commonly used desiccant that can efficiently adsorb moisture from the air due to its high surface area and porosity.
79. The adsorption of hydrogen on the surface of a transition metal like nickel at high temperature is an example of:
- a) Physisorption
- b) Chemisorption
- c) Both physisorption and chemisorption
- d) Multilayer adsorption
Answer: b) Chemisorption
Explanation: The adsorption of hydrogen on transition metals such as nickel at high temperatures involves chemical bond formation, which is characteristic of chemisorption.
80. In adsorption chromatography, the substance adsorbed is known as:
- a) Adsorbent
- b) Mobile phase
- c) Adsorbate
- d) Eluent
Answer: c) Adsorbate
Explanation: In adsorption chromatography, the substance that is adsorbed on the stationary phase is referred to as the adsorbate.
81. Which of the following is not a characteristic of chemisorption?
- a) It is highly specific.
- b) It is usually irreversible.
- c) It forms multilayers of adsorbate.
- d) It involves chemical bonds.
Answer: c) It forms multilayers of adsorbate
Explanation: Chemisorption forms a monolayer of adsorbate, as it involves strong chemical bonding with specific sites on the adsorbent surface. Multilayer formation is characteristic of physisorption.
82. Which of the following changes occur during adsorption?
- a) Enthalpy increases and entropy decreases.
- b) Enthalpy decreases and entropy decreases.
- c) Enthalpy increases and entropy increases.
- d) Enthalpy decreases and entropy increases.
Answer: b) Enthalpy decreases and entropy decreases
Explanation: Adsorption is an exothermic process (enthalpy decreases), and as the molecules become more ordered on the surface, the randomness or disorder of the system decreases (entropy decreases).
83. In physisorption, adsorption decreases with:
- a) Increase in temperature
- b) Increase in pressure
- c) Decrease in temperature
- d) Decrease in surface area
Answer: a) Increase in temperature
Explanation: Physisorption is favored at low temperatures because it involves weak Van der Waals forces. As temperature increases, the thermal energy of the adsorbate molecules increases, leading to desorption.
84. What is the main difference between chemisorption and physisorption?
- a) Chemisorption is non-specific, and physisorption is specific.
- b) Chemisorption requires activation energy, while physisorption does not.
- c) Chemisorption is reversible, while physisorption is irreversible.
- d) Chemisorption forms multilayers, while physisorption forms a monolayer.
Answer: b) Chemisorption requires activation energy, while physisorption does not
Explanation: Chemisorption involves the formation of chemical bonds, which often requires activation energy, whereas physisorption is governed by weak Van der Waals forces and does not require significant activation energy.
85. In which of the following adsorption processes is the enthalpy change the highest?
- a) Physisorption of CO₂ on activated charcoal
- b) Chemisorption of hydrogen on nickel
- c) Adsorption of nitrogen on silica gel
- d) Adsorption of water vapor on silica gel
Answer: b) Chemisorption of hydrogen on nickel
Explanation: Chemisorption involves the formation of strong chemical bonds, leading to a higher enthalpy change compared to the weak interactions involved in physisorption.
86. 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 fails at high pressure because it does not account for the saturation of the adsorbent, where no more adsorption can occur regardless of further increases in pressure.
87. At low temperatures, the adsorption of gas on solid is mainly:
- a) Chemisorption
- b) Physisorption
- c) Both physisorption and chemisorption
- d) Desorption
Answer: b) Physisorption
Explanation: Physisorption predominates at low temperatures because it involves weak Van der Waals forces. Chemisorption requires higher temperatures due to its need for activation energy.
88. Which of the following statements is incorrect regarding adsorption?
- a) Adsorption is a surface phenomenon.
- b) Adsorption is an endothermic process.
- c) Adsorption increases with an increase in surface area.
- d) Adsorption decreases with an increase in temperature.
Answer: b) Adsorption is an endothermic process
Explanation: Adsorption is an exothermic process, where heat is released when the adsorbate molecules adhere to the surface of the adsorbent.
89. What is the main assumption of the Langmuir adsorption isotherm?
- a) The surface is heterogeneous.
- b) Adsorption can occur at variable energies.
- c) All adsorption sites are equivalent.
- d) Multilayer adsorption occurs.
Answer: c) All adsorption sites are equivalent
Explanation: The Langmuir adsorption isotherm assumes that the adsorbent surface is homogeneous, with all adsorption sites being equivalent and able to hold only one molecule of adsorbate.
90. The efficiency of an adsorbent increases with:
- a) Decrease in surface area
- b) Decrease in particle size
- c) Increase in temperature
- d) Increase in pressure
Answer: b) Decrease in particle size
Explanation: Decreasing the particle size increases the surface area available for adsorption, making the adsorbent more efficient.
91. Which of the following best describes the adsorption of gases on a solid at high temperatures?
- a) Adsorption increases
- b) Adsorption decreases
- c) Adsorption is independent of temperature
- d) Adsorption increases at first and then decreases
Answer: b) Adsorption decreases
Explanation: Adsorption is an exothermic process, and increasing the temperature provides energy to the adsorbed molecules, causing them to desorb, thereby decreasing adsorption.
92. Which of the following is true for adsorption?
- a) Adsorption is spontaneous with a positive free energy change.
- b) Adsorption is non-spontaneous with a negative free energy change.
- c) Adsorption is spontaneous with a negative free energy change.
- d) Adsorption is non-spontaneous with a positive free energy change.
Answer: c) Adsorption is spontaneous with a negative free energy change
Explanation: Adsorption is spontaneous, meaning it occurs naturally, and the free energy change (ΔG) is negative. This is because the process results in a lower energy state.
93. Which of the following statements about chemisorption is incorrect?
- a) It is highly specific.
- b) It is reversible.
- c) It forms a monolayer.
- d) It involves the formation of chemical bonds.
Answer: b) It is reversible
Explanation: Chemisorption is typically irreversible due to the strong chemical bonds formed between the adsorbent and adsorbate.
94. In the adsorption of gases on solids, the plot of log x/mx/m versus log PP is a straight line with slope less than 1 in which isotherm?
- a) Langmuir isotherm
- b) BET isotherm
- c) Freundlich isotherm
- d) Temkin isotherm
Answer: c) Freundlich isotherm
Explanation: In the Freundlich adsorption isotherm, a plot of log x/mx/m (amount adsorbed per unit mass) versus log PP (pressure) gives a straight line with a slope less than 1, indicating the intensity of adsorption.
95. Which of the following is used to measure the surface area of an adsorbent?
- a) Freundlich adsorption isotherm
- b) BET adsorption isotherm
- c) Langmuir adsorption isotherm
- d) Van’t Hoff equation
Answer: b) BET adsorption isotherm
Explanation: The BET isotherm is widely used to determine the specific surface area of solids by analyzing gas adsorption data, especially in multilayer adsorption.
96. Adsorption of a gas on a solid is accompanied by a decrease in:
- a) Enthalpy only
- b) Entropy only
- c) Both enthalpy and entropy
- d) Neither enthalpy nor entropy
Answer: c) Both enthalpy and entropy
Explanation: Adsorption leads to a decrease in both enthalpy (because it is exothermic) and entropy (because the system becomes more ordered as molecules adhere to the solid surface).
97. Which of the following does not explain the mechanism of adsorption?
- a) Physical adsorption
- b) Chemisorption
- c) Le Chatelier’s principle
- d) Henry’s law
Answer: d) Henry’s law
Explanation: Henry’s law explains the solubility of gases in liquids, not the adsorption of gases on solid surfaces, which is better explained by physical adsorption, chemisorption, and Le Chatelier’s principle.
98. Which of the following is NOT involved in the adsorption process?
- a) Van der Waals forces
- b) Chemical bonds
- c) Covalent bonding
- d) Gravitational forces
Answer: d) Gravitational forces
Explanation: Gravitational forces are not involved in adsorption processes. Adsorption involves either weak Van der Waals forces (physisorption) or stronger chemical bonds (chemisorption).
99. In adsorption, when the rate of adsorption equals the rate of desorption, the system is said to be in:
- a) Chemical equilibrium
- b) Physical equilibrium
- c) Dynamic equilibrium
- d) Static equilibrium
Answer: c) Dynamic equilibrium
Explanation: In adsorption, when the rate of adsorption equals the rate of desorption, the system reaches dynamic equilibrium, where the amounts adsorbed and desorbed remain constant over time.
100. Which of the following correctly explains the relationship between temperature and chemisorption?
- a) Chemisorption increases with increasing temperature.
- b) Chemisorption decreases with increasing temperature.
- c) Chemisorption remains unaffected by temperature.
- d) Chemisorption first increases and then decreases with increasing temperature.
Answer: d) Chemisorption first increases and then decreases with increasing temperature
Explanation: Chemisorption requires activation energy, so it initially increases with temperature. However, at very high temperatures, desorption becomes significant, causing chemisorption to decrease.
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