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Surface chemistry is a chemical phenomenon which occurs at the interface of two surfaces. The surfaces identified can be solid-liquid, solid-gas, liquid-liquid, liquid-gas or gas-gas. It is a branch of chemistry that deals with the chemical changes that occur at an interface and also with properties of surfaces also known as phase boundaries. The phenomena based on the principle of surface chemistry includes: Catalysis, Colloidal formation, Electrode reactions, and Chromatography.
Surface Chemistry
Ques 1. The correct ascending order of adsorption of the following gases on the same mass of charcoal at same temperature and pressure is
(a) CH4 < H2 < SO2
(b) H2 < CH4 < SO2
(c) SO2 < CH4 < H2
(d) H2 < SO2 < CH4
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Answer: b
Explanation:
(b) The extent of adsorption increases with increase in polarity and molar mass so the correct option is b.
Ques 2. The formation of micelles takes place only above
(a) Inversion temperature
(b) Boyle’s temperature
(c) Critical temperature
(d) Kraft temperature
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Answer: d
Explanation:
(d) The temperature above which micelles formation takes place is called Kraft temperature.
Ques 3. Collodion is 4% solution of which one of the following in alcohol-ether mixture.
(a) Nitroglycerin
(b) Cellulose acetate
(c) Glycol dinitrate
(d) Nitrocellulose
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Answer: d
Explanation:
(d) Nitrocellulose when dissolved in 4% alcohol-ether mixture is called collodion
Ques 4. Freundlich adsorption isotherm is given by the expression xm = k p1/n which of the following conclusions can be drawn from this expression. [NCERT Exemplar]
(a) When 1n = 0, the adsorption is independent of pressure.
(b) When 1n = 0, the adsorption is directly proportional to pressure.
(c) When n = 0, xm vs p graph is a line parallel to x-axis.
(d) When n = 0, plot of xm vs p is a curve.
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Answer: a
Explanation:
(a) and (c) are correct, when n = 0.
∴ xm vs p graph is line parallel to x-axis.
when 1n = 0, xm is independent of pressure at high pressure.
Ques 5. H2 gas is adsorbed on activated charcoal to a very little extent in comparison to easily liquefiable gases due to. [NCERT Exemplar]
(a) very strong van der Waal’s interaction
(b) very weak van der Waals forces
(c) very low critical temperature
(d) very high critical temperature
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Answer: b
Explanation:
(b) and (c). It is due to weak van der Waals’ forces of attraction and very low critical temperature of H2 gas
Ques 6. The protective power of lyophilic colloidal sol is expressed in terms of
(a) coagulation value
(b) gold number
(c) CMC (Critical Micelle Concentration)
(d) oxidation numbers
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Answer: b
Explanation:
(b) Gold number is used to measure protective power of colloids. If the gold number is lowered, the protective power will increase, e.g., gelatin.
Ques 7. The coagulation values in millimoles per litre of the electrolyte for the coagulation of As2S3 sol are given
- NaCl (52)
- BaCl2 (0.69)
- MgSO4 (0.22)
The correct order of coagulating power is
(a) I > II > III
(b) II > I > III
(c) III > II > I
(d) III > I > II
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Answer: c
Explanation:
(c) III > II > I
\(\because\) Lesser the coagulation value, more is coagulating power meaning it is inversely proportional.
Ques 8. According to Freundlich adsorption isotherm, which of the following is correct?
(a) xm ∝ p1
(b) xm ∝ p1/n
(C) xm ∝ p°
(d) All are correct of different ranges of pressure
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Answer: d
Explanation:
(d) All are correct
(a) That is correct at low pressure,
(b) That is correct at moderate pressure and
(c) That is correct at high pressure (saturation pressure).
Ques 9. 3g of activated charcoal was added to 50 ml of acetic acid solution (0.06 M) in a flask. After an hour it was filtered and the strength of filtrate was found to be 0.042 M. The amount of acetic acid adsorbed per gram of charcoal is
(a) 42 mg
(b) 54 mg
(c) 18 mg
(d) 36 mg
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Answer: b
Explanation:
(b) Molarity of CH3COOH adsorbed
= 0.06 – 0.042 = 0.018
Number of milli moles of CH3COOH that are
adsorbed = 0.018 × 50 ml = 0.90
Final Amount = 0.90 × 60 = 54 mg
[\(\because\) molar mass of CH3COOH is taken as 60 g mol-1]
Ques 10. During the adsorption of gas on the surface of solid, which of the following is true?
(a) ΔG < 0, ΔH > 0, ΔS < 0 (b) ΔG > 0, ΔH < 0, ΔS < 0
(c) ΔG < 0, ΔH < 0, ΔS < 0
(d) ΔG < 0, ΔH < 0, ΔS > 0
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Answer: (c) ΔG < 0, ΔH < 0, ΔS < 0
Explanation:
(c) ΔG < 0 means process is spontaneous because adsorption is exothermic in nature, ΔH = negative and entropy is decreasing, i.e., ΔS will come out as negative.
Ques 11. The best coagulant for the precipitation of Fe(OH)3 sol is
(a) Na2HPO3
(b) NaNO3
(c) Na3PO4
(d) Na2SO4
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Answer: c
Explanation:
(c) PO3−4 works in most effective way for positively charged Fe(OH)3sol due to higher charge.
Ques 12. Which is favorable for physical adsorption?
(a) High T and high P
(b) High T and low P
(c) Low T and high P
(d) T and P do not affect
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Answer: c
Explanation:
(c) Low temperature and high pressure provide help in increased physical adsorption because van der Waals’ forces of attraction will increase.
Ques 13. Which of the following statements are correct about solid catalyst? [NCERT Exemplar]
(a) Same reactants may give different product by using different catalysts.
(b) Catalyst does not change AH of reaction.
(c) Catalyst is required in large quantities to catalyze reactions.
(d) Catalytic activity of a solid catalyst does not depend upon the strength of chemisorption.
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Answer: a
Explanation:
(a) It is called selectivity of catalyst as per requirement.
(b) Catalyst changes only the EA (Activation energy) of the reaction.
Ques 14. The stability of lyophobic sols is due to
(a) adsorption of covalent molecules on the colloid
(b) the size of the particles
(c) the charge on particles
(d) Tyndall effect.
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Answer: c
Explanation:
(c) same charge on particles causes repulsion which further allows particles to settle down.
Ques 15. Gold sol can be prepared by
(a) Hydrolysis of AUCl3
(b) Oxidation of Gold by aqua-regia
(c) Peptization
(d) Reduction of AUCl3 with HCHO solution.
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Answer: d
Explanation:
(d) 2AuCl3 + 3HCHO + 3H2O → 2Au + 3HCOOH + 6HCl
Ques 16. The term ‘sorption’ stands for ___________ . [NCERT Exemplar]
(a) absorption
(b) adsorption
(c) both absorption and adsorption
(d) desorption
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Answer: c
Explanation:
(c) When both the processes of adsorption and absorption take place, it is called sorption, e.g., dying of cotton fiber.
Ques 17. Extent of adsorption of adsorbate from solution phase increases with __________ [NCERT Exemplar]
(a) increase in amount of adsorbate in solution.
(b) decrease in surface area of adsorbent.
(c) increase in temperature of solution.
(d) decrease in amount of adsorbate in solution.
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Answer: a
Explanation:
(a) xm = k C1/n [where ‘C’ is concentration of solution]
Ques 18. Physical adsorption of a gaseous species may change to chemical adsorption with ___________ . [NCERT Exemplar]
(a) decrease in temperature
(b) increase in temperature
(c) increase in surface area of adsorbent
(d) decrease in surface area of adsorbent
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Answer: b
Explanation:
(b) At high temperature, covalent bonds will be seen forming as activation energy will be provided.
Ques 19. On the basis of data given below predict which of the following gases shows least adsorption on a definite amount of charcoal? [NCERT Exemplar]
(a) CO2
(b) SO2
(c) CH4
(d) H2
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Answer: b
Explanation:
(b) SO2, Because of higher critical temperature, the Van der Waal’s forces of attraction will be more which would result in increased extent of adsorption.
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