This article contains MCQ Questions from Chemistry Chapter "Surface Chemistry".

## Surface Chemistry Assignment 1 - Questions

**Q1. **The adsorption of a gas on a solid surface exhibits the following isotherm. Which one of the following statements is true?

- Heat of adsorption is independent of coverage
- Adsorption is multilayer
- Heat of adsorption varies monotonically with coverage
- Heat of adsorption varies exponentially with coverage.

**Q2.** Isothermal which has fractional coverage, linearly, dependent on pressure at low pressures but almost independent at high pressure is called

- BET isotherm
- Langmuir isotherm
- Freundlich isotherm
- Temkin isotherm

**Q3. **The Langmuir adsorption isotherm is given by = kp/(1+kp), where P is the pressure of the adsorbate gas. The Langmuir adsorption isotherm for a diatomic gas A_{2} undergoing dissociative adsorption is:

- Î¸ = kp/(1+kp)
- Î¸ = 2kp/(1+2kp)
- Î¸ = kp
^{2}/(1+(kp)^{2}) - Î¸ = (kp)
^{1/2}/(1+kp)^{1/2}

**Q4.** Dispersion of a solid in a liquid, a liquid in a gas and a liquid in a liquid are respectively known as

- Aerosol, emulsion, sol
- Emulsion, sol, aerosol
- sol, Aerosol, emulsion
- Aerosol, sol, emulsion

**Q5.** The figure below depicts an adsorption isotherm of O_{2}, on charcoal at 90 K.

At a pressure 25 torr, only 10% of charcoal sites are occupied by O_{2}. Therefore, the ratio of adsorption to desorption rate constants (in torr^{−1}) is close to

- 0.003
- 0.004
- 0.006
- 0.015

**Q6. **For the non dissociative Langmuir type adsorption of a gas on a solid surface at a particular temperature, the fraction of surface coverage is 0.6 at 30 bar. The Langmuir isotherm constant (in bar^{−1} units) at this temperature is

- 0.05
- 0.20
- 2.0
- 5.0

**Q7.** Hydrogen is adsorbed on many metal surfaces by dissociation (S represents a surface site)-

If the pressure of H_{2} (p) is small, the fraction of the surface covered by hydrogen is proportional to

- p
- p
^{2} - p
^{1/2} - p
^{1/4}

**Q8. **A graph plotted log x/m vs log P shows a straight line with slope equal to 1 and intercept equal to 0.4771. The extent of adsorption of gas at pressure 2 atm is:

- 1.4
- 6.0
- 4.1
- 3.2

**Q9. **According to Langmuir isotherm theory of adsorption, which of the following statements is not correct?

- surface of solid is homogeneous
- the gaseous molecules are localized
- there is a strong interaction between the molecules
- monolayer formation takes place

**Q10.** Variation of Î¸ with pressure for a tetra-atomic molecule in low pressure region (dissociative mechanism) is best defined as:

- Î¸ x P
^{1/2} - Î¸ x P
- Î¸ x P
^{1/4} - Î¸ x P
^{4}

**Q11.** For small coverage, the plot of ln(Î¸/p) vs Î¸ gives a straight line with slope equal to

- -1
- 1
- 0
- infinite

**Q12.** For a diatomic gas, the pressure according to Langmuir adsorption isotherm (dissociative mechanism) is:

- None of these

**Q13.** Adsorption is accompanied with

- decrease in enthalpy of the system
- decrease in entropy
- Value of ∆ S.T is negative
- All of these

**Q14.** The adsorption of a gas is described by the Langmuir isotherm with K = 0.85 kPa-1 at 25oC. Calculate the pressure at which the fractional surface coverage is 0.95.

- 22.35 Pa
- 22.35 kPa
- 0.57 kPa
- 0.57 Pa

**Q15.** The maximum observed enthalpies of physisorption are -21 and -59 KJ mol^{-1} respectively for gases A and B. The A and B can be

- H
_{2}O and CH_{4} - CH
_{4}and N_{2} - CH
_{4}and H_{2}O - N
_{2}and CH_{4}

**Q16. **How long a gaseous atom will stay on the adsorbent surface at 278 K if its desorption activation energy is 30 KJ mol^{-1}? (Î³_{o}=10^{-13} sec)

Given e^{13} = 4.42 × 10^{5} , e^{12} = 1.6 × 10^{-5}

- 4.33 × 10
^{-8} - 1.01 × 10
^{-13} - 1.81 × 10
^{-8} - 3.66 × 10
^{-13}

**Q17.** Adsorption of CO on charcoal at 273 k follows Langmuir isotherm. A plot of P (kPa) /V (cm^{3}) vs P is linear with slope of 0.01 and y-intercept is 0.05. The equilibrium constant, K, for the adsorption is:

- 0.2 × 10
^{-2} - 5 × 10
^{-3} - 0.2
- 0.05

**Q18. **In an experiment, it was found that 0.106 mg of stearic acid covered 1000 cm^{2} on water surface. Find the thickness of stearic acid film. (Density of stearic acid = 0.85 g cm^{-3}, molar mass = 284 g mol^{-1})

- 1.24 × 10
^{-7}cm - 1.24 × 10
^{-7}m - 1.24 × 10
^{-7}nm - 1.24 × 10
^{-7}mm

## Surface Chemistry Answer Key

1. (1), 2. (2), 3. (4), 4. (2), 5. (2), 6. (1), 7. (3), 8. (2), 9. (3), 10. (3), 11. (3), 12. (4), 13. (4), 14. (2), 15. (3), 16. (1), 17. (3), 18. (1)

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