Physical Chemistry - Surface Chemistry
Q. In the Langmuir adsorption isotherm, which assumption is NOT made? (2019)
A.
Adsorption occurs on a surface with a finite number of identical sites
B.
Adsorption is reversible
C.
There is no interaction between adsorbed molecules
D.
Adsorption occurs only at high pressures
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Solution
The Langmuir isotherm assumes that adsorption occurs at all pressures, not just high pressures.
Correct Answer: D — Adsorption occurs only at high pressures
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Q. The Freundlich adsorption isotherm is best described by which equation? (2023)
A.
x/m = kP
B.
x/m = kP^(1/n)
C.
P = k(x/m)
D.
P = k(x/m)^(1/n)
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Solution
The Freundlich isotherm is represented by the equation x/m = kP^(1/n), where x is the amount adsorbed, m is the mass of the adsorbent, and P is the pressure.
Correct Answer: B — x/m = kP^(1/n)
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Q. What is the primary difference between physisorption and chemisorption? (2023)
A.
Physisorption is stronger than chemisorption
B.
Chemisorption involves chemical bonds, while physisorption involves van der Waals forces
C.
Physisorption is irreversible, while chemisorption is reversible
D.
Chemisorption occurs at lower temperatures than physisorption
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Solution
The primary difference is that chemisorption involves the formation of chemical bonds, while physisorption involves weaker van der Waals forces.
Correct Answer: B — Chemisorption involves chemical bonds, while physisorption involves van der Waals forces
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Q. What is the term for the maximum amount of adsorbate that can be adsorbed on a given mass of adsorbent? (2020)
A.
Adsorption capacity
B.
Saturation point
C.
Equilibrium concentration
D.
Adsorption isotherm
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Solution
The maximum amount of adsorbate that can be adsorbed on a given mass of adsorbent is referred to as the adsorption capacity.
Correct Answer: A — Adsorption capacity
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Q. Which of the following is a characteristic of multilayer adsorption? (2019)
A.
Occurs at low pressures only
B.
Described by the Langmuir isotherm
C.
Described by the BET theory
D.
Involves only physical adsorption
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Solution
Multilayer adsorption is described by the BET theory, which accounts for the formation of multiple layers of adsorbate on the adsorbent.
Correct Answer: C — Described by the BET theory
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Q. Which of the following is NOT a method for measuring surface area of adsorbents? (2022)
A.
BET method
B.
Langmuir method
C.
TGA method
D.
Gas adsorption method
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Solution
Thermogravimetric analysis (TGA) is not a method for measuring surface area; it is used to study thermal stability and composition.
Correct Answer: C — TGA method
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