Surface Chemistry — Advanced Notes & 50 MCQs

1. Adsorption differs from absorption in that adsorption:

1. Occurs throughout the bulk of material
2. Occurs only at the surface ✅
3. Is always irreversible
4. Does not depend on surface area

2. Physisorption is characterized by:

1. High activation energy
2. Low heat of adsorption and reversibility ✅
3. Covalent bond formation
4. Irreversibility at all temperatures

3. The Langmuir adsorption isotherm assumes:

1. Multilayer adsorption
2. Monolayer adsorption on homogeneous sites ✅
3. Heterogeneous surface with varying energies
4. No saturation at high pressure

4. In Freundlich isotherm, the relation between amount adsorbed (x/m) and pressure p is:

1. x/m = k p / (1 + k p)
2. x/m = k p^(1/n) (empirical) ✅
3. x/m = k ln p
4. x/m = k / p

5. BET theory is mainly used to determine:

1. Pore size distribution only
2. Specific surface area of solids ✅
3. Activation energy of adsorption
4. Only chemisorption heat

6. Which of the following increases adsorption of gas on solid surface?

1. Increase in temperature for physisorption
2. Increase in pressure ✅
3. Decrease in surface area
4. Adding inert gas always decreases adsorption

7. Chemisorption differs from physisorption because it:

1. Is governed solely by van der Waals forces
2. Involves chemical bond formation and often higher heat of adsorption ✅
3. Is always multilayered
4. Never shows specificity for adsorbate

8. Surface area plays a crucial role in catalysis because:

1. Only bulk properties matter
2. Higher surface area provides more active sites for reactions ✅
3. Surface area reduces adsorption always
4. Catalysis is independent of surface properties

9. Which mechanism describes reaction between two adsorbed species on catalyst surface?

1. Eley-Rideal
2. Langmuir-Hinshelwood ✅
3. Michaelis-Menten
4. Arrhenius only

10. In Eley–Rideal mechanism:

1. Both reactants are adsorbed before reaction
2. One reactant adsorbs and reacts directly with another from the gas phase ✅
3. Reaction occurs only in bulk solution
4. No adsorption is involved

11. Poisoning of catalyst occurs when:

1. Catalyst is heated to high temp
2. Impurities bind to active sites reducing activity ✅
3. Surface area increases dramatically
4. Catalyst dissolves completely

12. A colloid is defined as a dispersion where particle size lies approximately between:

1. 0.001–0.01 nm
2. 1–1000 nm ✅
3. 1–10 mm
4. Greater than 1 cm

13. Which phenomenon demonstrates colloidal nature by scattering light?

1. Tyndall effect ✅
2. Brownian motion only
3. Ostwald ripening
4. Coagulation only

14. Brownian motion in colloids is caused by:

1. Gravity only
2. Collision with solvent molecules ✅
3. Magnetic forces only
4. None of the above

15. Which stabilizes lyophobic colloids primarily?

1. Steric stabilization only
2. Electrical double layer (electrostatic) stabilization ✅
3. Gravity
4. None — they are always unstable

16. Coagulation of colloids can be achieved by adding:

1. Alcohols only
2. Electrolytes (opposite charge neutralization) ✅
3. Detergents only
4. Inert gases

17. Critical coagulation concentration (CCC) depends on:

1. Only temperature
2. Valency of ions and colloid surface charge ✅
3. Only size of colloid particles
4. Only pH

18. Which of the following is an emulsifying agent?

1. Sodium chloride
2. Soap or detergent ✅
3. Acetone
4. Pure water

19. Micelles are formed when surfactant concentration exceeds:

1. CMC — critical micelle concentration ✅
2. CCC only
3. pH point of zero charge
4. None of the above

20. Which is NOT true for catalysts?

1. They increase reaction rate
2. They change equilibrium position ✅
3. They provide alternate pathway with lower Ea
4. They are regenerated at end of reaction

21. Heterogeneous catalysis typically occurs on:

1. Uniform solution phase only
2. Surface of solid catalyst ✅
3. Gas phase exclusively
4. None of the above

22. Turnover frequency (TOF) measures:

1. Amount of catalyst used
2. Number of reactant molecules converted per active site per unit time ✅
3. Surface area only
4. Only adsorption energy

23. Which property of colloids causes them to be stable against sedimentation?

1. High density of particles
2. Brownian motion (thermal motion) ✅
3. Large particle size
4. Absence of charge

24. Which of the following is an example of a lyophobic sol?

1. Starch in water
2. Gold sol ✅
3. Sugar solution
4. Alcohol in water

25. Emulsions are stabilized by adding:

1. Electrolytes only
2. Emulsifying agents (surfactants) ✅
3. Strong acids only
4. Pure solvents only

26. Which term describes surface atoms with unsatisfied bonds leading to higher reactivity?

1. Bulk atoms
2. Surface defects or coordinatively unsaturated sites ✅
3. Interiors
4. None of the above

27. Which adsorption isotherm is linear when plotted as log x/m vs log p?

1. Langmuir
2. Freundlich ✅
3. BET
4. Henry's law only

28. Surface tension arises due to:

1. Attractive forces between bulk molecules only
2. Unbalanced cohesive forces at liquid surface ✅
3. Thermal agitation only
4. None of the above

29. Which instrument measures surface tension by the drop weight method?

1. Ostwald viscometer
2. Tensiometer (drop weight or Du Noüy ring method) ✅
3. pH meter
4. Mass spectrometer

30. In heterogeneous catalysis, promoters are used to:

1. Deactivate catalyst
2. Enhance activity or selectivity of catalyst ✅
3. Increase poisoning
4. Only change color

31. Which is an example of a colloidal gas in liquid?

1. Foam (e.g., whipped cream) ✅
2. Hydrosol only
3. Emulsion only
4. Alloys

32. Zeta potential is used to quantify:

1. Color of colloid
2. Stability of colloidal dispersion (electrostatic repulsion) ✅
3. Only viscosity
4. None of the above

33. Which process describes the increase in average particle size in colloids over time?

1. Coagulation
2. Ostwald ripening ✅
3. Brownian motion
4. Adsorption only

34. Which type of colloid is milk?

1. Gaseous sol in liquid
2. Liquid emulsion of fat in water ✅
3. Solid in gas
4. Solid in solid

35. Which factor favors chemisorption over physisorption?

1. Low temperature generally ✅ (but chemisorption may require activation and optimal moderate temp)
2. Very high pressures only
3. Absence of surface sites
4. Inert surfaces only

36. Which of the following is used as a catalyst support to increase dispersion?

1. Bulk metal plate
2. High surface area oxides like Al2O3 or SiO2 ✅
3. Pure water
4. None of the above

37. Which phenomenon is responsible for detergent action?

1. Reduction of surface tension and formation of micelles ✅
2. Increase of surface tension only
3. Complete dissolution of dirt in water
4. Electrolysis of water

38. The rate law for surface reactions often depends on:

1. Only bulk concentration always
2. Coverage of adsorbed species on the surface (θ) ✅
3. Only temperature
4. None of the above

39. Which ion typically stabilizes positively charged colloids?

1. Other positive ions
2. Anions in the electrical double layer ✅
3. Neutral molecules only
4. None of the above

40. Which of the following increases with increasing particle size in a colloid?

1. Brownian motion speed
2. Sedimentation rate (larger particles settle faster) ✅
3. Tyndall scattering intensity always decreases
4. Stability always increases

41. Which test distinguishes between true solution and colloid?

1. Color test only
2. Tyndall effect (light scattering) ✅
3. pH measurement only
4. Boiling point elevation

42. Which is true for adsorption at constant temperature when pressure increases for physisorption?

1. Amount adsorbed decreases
2. Amount adsorbed increases until saturation ✅
3. No change
4. Immediate desorption

43. Which of the following is used for de-emulsification in industry?

1. Adding more emulsifier
2. Demulsifiers (chemicals) or heating ✅
3. Only shaking vigorously
4. Adding surfactant always stabilizes

44. The heat of adsorption for chemisorption compared to physisorption is:

1. Much lower
2. Much higher (stronger bonding) ✅
3. Approximately equal
4. Negligible

45. Which of the following best describes an aerosol?

1. Liquid dispersed in liquid
2. Solid or liquid particles dispersed in gas ✅
3. Gas dispersed in liquid only
4. Solid dispersed in solid

46. Which surface character helps adsorption of polar molecules?

1. Hydrophobic nonpolar surface
2. Polar or charged surface groups ✅
3. Completely inert surface
4. None of the above

47. Which law relates pressure of gas to amount adsorbed at low pressures linearly?

1. Langmuir law
2. Henry's law (at low coverages) ✅
3. Freundlich law only
4. Raoult's law

48. Which of the following processes reduces surface area of a powder most effectively?

1. Grinding to smaller particles
2. Sintering or agglomeration (particles fuse) ✅
3. Dispersing in solvent
4. Ultrasonic dispersion

49. Which of these is a measure of surface activity of a surfactant?

1. Melting point only
2. Critical micelle concentration (CMC) ✅
3. Boiling point
4. Vapor pressure