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.
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