CBSE Class 12 Chemistry Surface Chemistry Assignment

Question. The adsorption of a gas on a solid surface varies with pressure of the gas in which of the following manner
(a) fast → slow → independent of the pressure
(b) slow → fast → independent of the pressure
(c) independent of the pressure → fast → slow
(d) independent of the pressure → slow → fast
Answer : A

Question. 1g of charcoal adsorbs 100 mL 0.5 M CH₃COOH to form a monolayer, and thereby the molarity of CH₃COOH reduces to 0.49. Calculate the surface area of the charcoal covered by each molecule of acetic acid. Surface area of charcoal = 3.01 × 10² m²/g.
(a) 0.5 × 10^–19 m²
(b) 4 × 10–20 m²
(c) 0.5 × 10–10 m²
(d) 5 × 10^–19 m²
Answer : D

Question. 3.6 gram of oxygen is adsorbed on 1.2 g of metal powder. What volume of oxygen adsorbed per gram of the adsorbent at 1 atm and 273 K?
(a) 0.19 Lg^–1
(b) 1 Lg^–1
(c) 2.1 Lg^–1
(d) None of these
Answer : C

Question. Flocculation value of BaCl₂ is much less than that of KCl for sol A and flocculation value of Na₂SO₄ is much less than that of NaBr for sol B.
The correct statement among the following is
(a) Both the sols A and B are negatively charged.
(b) Sol A is positively charged and Sol B is negatively charged.
(c) Both the sols A and B are positively charged.
(d) Sol A is negatively charged and sol B is positively charged.
Answer : B

Question. Consider the following statements about Langmuir isotherm.
I. The free gas and adsorbed gas are in dynamic equilibrium.
II. All adsorption sites are equivalent.
III. The initially adsorbed layer can act as a substrate for further adsorption
IV. The ability of a molecule to get adsorbed at a given site is independent of the occupation of neighboring sites.
The correct statements are
(a) I, II, III and IV
(b) I, II and IV
(c) I, III and IV
(d) I, II and III
Answer : B

Question. Freshly obtained SnO₂ is added to water containing a little HCl. The sol obtained would be ................ due to preferential adsorbtion of ................... ions
(a) positively charged, H⁺
(b) negatively charged, SnO₃^2–
(c) positively charged, Sn⁴⁺
(d) positively charged, Sn²⁺
Answer : C

Question. One desires to prepare a positively charged sol of silver iodide. This can be achieved by
(a) adding a little AgNO₃ solution to KI solution in slight excess
(b) adding a little KI solution to AgNO₃ solution in slight excess
(c) mixing equal volumes of equimolar solutions of AgNO₃ and KI
(d) None of these
Answer : B

Question. The curve that best describes the adsorption of a gas (X g) on 1.0 g of a solid substrate as a function of pressure (p) at a fixed temperature is

(a) 1
(b) 2
(c) 3
(d) 4
Answer : B

Question. Which one of the following is an example of homogeneous catalysis ?
(a) Haber’s process of synthesis of ammonia 
(b) Catalytic conversion of SO₂ to SO₃ in contact process
(c) Catalytic hydrogenation of oils
(d) Acid hydrolysis of methyl acetate
Answer : D

Question. Which of the following statements about a catalyst is/are true ?
(a) A catalyst accelerates the reaction by bringing down the free energy of activation
(b) A catalyst also takes part in the reaction mechanism
(c) A catalyst makes the reaction more feasible by making the ΔGº more negative
(d) A catalyst makes the equilibrium constant of the reaction more favourable for the forward reaction.
Answer : A

Question. 100 mL each of two sols of AgI, one obtained by adding AgNO₃ to slight excess of KI and another obtained by adding KI to slight excess of AgNO₃, are mixed together. Then
(a) The two sols will stabilize each other
(b) The sol particles will acquire more electric charge
(c) The sols will coagulate each other mutually
(d) A true solution will be obtained
Answer : C

Question. Under the influence of an electric field, the particles in a sol migrate towards cathode. The coagulation of the same sol is studied using NaCl, Na₂SO₄ and Na₃PO₄ solutions. Their coagulating values will be in the order
(a) NaCl > Na₂SO₄ > Na₃PO₄
(b) Na₂SO₄ > Na₃PO₄ > NaCl
(c) Na₃PO₄ > Na₂SO₄ > NaCl
(d) Na₂SO₄ > NaCl > Na₃PO₄
Answer : A

Question. Which of the following is true in respect of chemical adsorption?
(a) ΔH < 0, ΔS > 0, ΔG > 0
(b) ΔH < 0, ΔS < 0, ΔG < 0
(c) ΔH > 0, ΔS > 0, ΔG < 0
(d) ΔH > 0, ΔS < 0, ΔG > 0
Answer : B

Question. In an experiment, 200 mL of 0.5 M oxalic acid is shaken with 10 g of activated charcoal and filtered. The concentration of the filtrate is reduced to 0.4 M. The amount of adsorption (x/m) is
(a) 0.9
(b) 1.8
(c) 0.18
(d) 0.09
Answer : C

Question. For a gas-solid adsorbent system, the adsorption isotherm x/m = Kp^1/n is applicable, where n = 5 in the specified case. Point out the correct statement :
(a) (x/m)Vs.p plot is a linear graph with slope equal to 5
(b) (x/m)Vs.log x Vs.p log plot is a straight line with slope equal to 5
(c) log(x/m) x Vs. log p is a straight line with slope equal to 0.2
(d) none of these
Answer : C

Question. In an experiment, addition of 4.0 mL of 0.005M BaCl₂ to 16.0 ml of arsenius sulphide sol just causes the complete coagulation in 2 hrs. The flocculating value of the effective ion is
(a) Cl^–, 1.0
(b) Cl^–, 2.0
(c) Ba²⁺, 1.0
(d) Ba²⁺, 0.5
Answer : C

Question. The most appropriate method of making egg– albumin sol is :
(a) Break an egg carefully and transfer the transparent part of the content to 100 mL of 5% w/V saline solution and stir well.
(b) Keep the egg in boiling water for 10 minutes. After removing the shell, transfer the yellow part of the content to 100 mL of 5% w/V saline solution and homogenize with a mechanical shaker.
(c) Keep the egg in boiling water for 10 minutes. After removing the shell, transfer the white part of the content to 100 mL of 5% w/V saline solution and homogenize with a mechanical shaker
(d) Break an egg carefully and transfer only the yellow part of the content to 100 mL of 5% w/V saline solution and stir well.
Answer : A

Question. To an emulsion of olive oil and water, stabilized by soap of alkali metals, a small amount of salts of bivalent or tervalent cations is added. Then
(a) stabilization of emulsion enhances
(b) the emulsion breaks into the component liquids
(c) reversal of phase to W/O type takes place
(d) the emulsion turns into a true solution
Answer : C

Question. The density of gold is 19 g/cm3. If 1.9 × 10^–4 g of gold is dispersed in one litre of water to give a sol having spherical gold particles of radius 10 nm, then the number of gold particles per mm³ of the sol will be :
(a) 1.9 × 10¹²
(b) 6.3 × 10¹⁴
(c) 6.3 × 10¹⁰
(d) 2.4 × 10⁶
Answer : D

Question. The volume of a colloidal particle, V_C as compared to the volume of a solute particle in a true solution V_S , could be
(a) V_C/V_S ≃ 10³
(b) V_C/V_S ≃ 10^-3
(c) V_C/V_S ≃ 10²³
(d) V_C/V_S ≃ 1
Answer : A

Numeric Value Answer

Question. In an adsorption experiment, a graph between log (x/m) versus log P was found to be linear with a slope of 45°. The intercept on the y axis was found to be 0.301. The amount of the gas adsorbed per gram of charcoal under a pressure of 3.0 atm is ________.
Answer : 6

Question. Considering Freundlich adsorption isotherm in this plot, find the extent of adsorption at a pressure of 4 atm.

Answer : 8

Question. The density of gold is 19 g/cm³. 1.9 × 10^–3 g of gold is dispersed in one litre of water to give a sol having spherical gold particles of radius 10.5 nm.
The gold particles are occupying 50% of the available space. The number of gold particles per mm3 is about 10ⁿ. Find the value of n.
Answer : 7

Question. 10% sites of catalyst bed have adsorbed by H₂. On heating H₂ gas is evolved from sites and collected at 0.03 atm and 300 K in a small vessel of 2.46 cm³. No. of sites available is 5.4 × 10¹⁶ per cm² and surface area is 1000 cm². Find out the no. of surface sites occupied per molecule of H₂.
(Given NA = 6 × 10²³)
Answer : 3

Question. The coagulation of 400 mL of a positive colloid took place when 1.46 g of HCl was added to it without changing the volume much. What is the flocculation value of HCl for the colloid?
Answer : 100

Question. A sample of 16 g charcoal was brought into contact with CH₄ gas contained in a vessel of 1 litre at 27 °C. The pressure of gas was found to fall from 760 to 608 torr. The density of charcoal sample is 1.6 g/cm3. What is the volume of the CH₄ gas adsorbed per gram of the adsorbent at 608 torr and 27 °C?
Answer : 16.25

Question. A cationic colloidal electrolyte forms micelle at 10^–3 M concentration in water. Its 1 mm³ solution contains 2 × 10¹³ micelle structures. What is the number of cations contained in one micelle? Take NA = 6 × 10^23.
Answer : 30

Question. One gram of activated carbon has a surface area of 1000 m². Considering complete coverage as well as monomolecular adsorption, how much ammonia at 1 atm and 273 K would be adsorbed on the surface of 44/7 g carbon if radius of a ammonia molecules is 10^–8 cm.
Answer : 7.46

Question. The coagulation of 100 mL of a colloidal sol of gold is completely prevented by addition of 250 mg of a substance to it before adding 10 mL of 1% NaCl solution. What is the gold number of this substance?
Answer : 25

Question. A detergent (C₁₂H₂₅SO₄^-Na⁺ ) solution becomes a colloidal sol at a concentration of 10^–3 M. On an average 10¹³ colloidal particles are present in 1 mm₃. What is the average number of ions which are contained by onecolloidal particle (micelle)?
Answer : 60
 

VSA QUESTIONS (1 - MARKS QUESTIONS )

1. Why does a gas mixed with another gas not form a colloidal system?

2. Why are adsorbate particles attracted and retained on the surface of adsorbent?

3. Explain the terms sorption and desorption.

4. “Chemisorption is highly specific.” Illustrate with an example.

5. “Adsorbents in finely divided form are more effective.” Why?

6. Name two compounds used as adsorbent for controlling humidity.
[Ans. : Silica gel, Alumina gel]

7. Mention one shape selective catalyst used to convert alcohol directly into gasoline.

8. ‘Generally high temperature is favourable for chemisorption.’ Why?

9. Name the catalyst used in the following process :

(a) Haber’s process for the manufacture of NH3 gas.

(b) Ostwald process for the manufacture of nitric acid.

10. Explain the relationship given by Freundlich in adsorption isotherm.

11. Which group elements show maximum catalytic activity for hydrogenation reactions?
[Hint : 7–9 group elements]

12. Why gas masks are used by miners in coal mines while working?

13. Write the chemical reaction involved in the preparation of sulphur sol.

14. Name the enzyme which converts milk into curd. [Ans. : lactobacilli]