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.
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