VBQs Surface Chemistry Class 12 Chemistry

VBQs Surface Chemistry Class 12 Chemistry with Surface Chemistry has been provided below for standard students. We have provided chapter wise VBQ for Class 12 Chemistry with Surface Chemistry. The following Surface Chemistry Class 12 Chemistry value based questions with answers will come in your exams. Students should understand the concepts and learn the solved cased based VBQs provided below. This will help you to get better marks in class 12 examinations.

Surface Chemistry VBQs Class 12 Chemistry

Case I : Read the passage given below and answer the following questions.

A graph between the amount adsorbed (x/m) by an adsorbent and the equilibrium pressure of the adsorbate at a constant temperature is called the adsorption isotherm.
A relationship between the amount adsorbed (x/m) and the equilibrium pressure (P) can be obtained as follows :

In the intermediate range of pressure, x/m = kP^1/n (was originally put forward by Freundlich and is known as Freundlich adsorption isotherm).

Question. Plot of log x/m against log p is a straight line inclined at an angle of 45°. When the pressure is 0.5 atm and Freundlich parameter, k is 10, the amount of solute adsorbed per gram of adsorbent will be (log 5 = 0.6990)
(a) 1 g
(b) 2 g
(c) 3 g
(d) 5 g

Question. In the adsorption of a gas on solid, Freundlich isotherm is obeyed. The slope of the plot is zero.Then the extent of adsorption is
(a) directly proportional to the pressure of the gas
(b) inversely proportional to the pressure of the gas
(c) directly proportional to the square root of the pressure of the gas
(d) independent of the pressure of the gas.

Question. In the Freundlich adsorption isotherm equation
log.x/m= logk + 1/n.logp ,the value of 1/n is
(a) any value from 0 to 1
(b) a negative integer
(c) a positive integer
(d) a positive or a negative fractional number.

Question. According to Freundlich adsorption isotherm,which of the following is correct?

(d) All the above are correct for different range of pressure.

Question. In the plot of log x/m vs log p for an adsorption, a straight line inclined at an angle of q = 14.04° to the x-axis was obtained. The ‘n’ value for this adsorption process is (tan 14.04° = 0.25)
(a) 5
(b) 8
(c) 4
(d) 2

Case II : Read the passage given below and answer the following questions.

Adsorption is a spontaneous process and involves unequal distribution of the molecules of the gaseous substance on the surface of solid or liquid. Adsorption is an exothermic process.
The attractive forces between adsorbate and adsorbent are either van der Waals’ forces or chemical bonds. Adsorption of gases on solids is generally controlled by the factors like temperature, pressure and nature of adsorbate and adsorbent.

Question. Which of the following graph represents the variation of physical adsorption with temperature?

Question. Which one of the following processes does not use adsorption?
(a) Froth floatation process
(b) Chromatography
(c) Decolourisation of sugar liquors
(d) Dissolution of sugar in water

Question. Methylene blue, from its aqueous solution, is adsorbed on activated charcoal at 25°C. For this process, the correct statement is
(a) the adsorption requires activation at 25°C
(b) the adsorption is accompanied by a decrease in enthalpy
(c) the adsorption increases with increase of temperature
(d) the adsorption is irreversible.

Question. In physisorption process, the attractive forces between adsorbate and adsorbent are
(a) covalent bonds
(b) ionic bonds
(c) van der Waals’ forces
(d) H-bonds.

Question. Which of the following statements is true?
(a) Chemisorption forms unimolecular layer.
(b) Chemisorption is a reversible process.
(c) Chemisorption is independent of pressure.
(d) Chemisorption has low enthalpy change.

Case III : Read the passage given below and answer the following questions.

Hardy Schulze rule states that the precipitating effect of an ion on dispersed phase of opposite charge increases with the valency of the ion.The higher the valency of the flocculating ion, the greater is its precipitating power.
Thus, for the precipitation of As₂S₃ sol (–ve sol) the precipitating power of Al³⁺, Ba²⁺ and Na⁺ ions is of the order, Al³⁺ > Ba²⁺ > Na⁺.
Similarly, for precipitating Fe(OH)₃ sol(+ve sol) the precipitating power of [Fe(CN)₆]^3–,SO₄^2– and Cl– is of the order, [Fe(CN)₆]^3– >SO₄^2– > Cl^–. The minimum concentration of an electrolyte in millimoles per litre required to cause precipitation of a sol in 2 hours is called flocculation value. The smaller the flocculation value, the higher will be the coagulating power of the ion. The minimum mass of the protective colloid (lyophilic colloid) in milligrams that must be added to 10 mL of a standard red gold sol so that no coagulation occurs when 1 mL of 10% NaCl solution is rapidly added to it is called the gold number of the protective colloid.

Question. The gold number of four protective colloids A, B, C and D are 0.03, 0.003, 10 and 30 respectively. Protective power of these colloids will be of the order :
(a) B > A > C > D
(b) A > B > C > D
(c) C > B > D > A
(d) D > A > C > B

Question. 1 mol of AgI/Ag+ is coagulated by
(a) 1 mol of KI
(b) 200 mL of 1 M K₂SO₄
(c) 300 mL of 1 M Na₃PO₄
(d) 2 mol of AgI

Question. The coagulation value in millimoles per litre of electrolytes used for the coagulation of As₂S₃ are as below :
I. NaCl = 52
II. KCl = 50
III. BaCl₂ = 0.69
IV. MgSO₄ = 0.72
The correct order of their flocculating power is
(a) I > II > III > IV
(b) I > II > IV > III
(c) I < II < IV < III
(d) IV < I < II < III

Question. Which of the following colloidal solutions is positively charged?
(a) TiO₂
(b) As₂S₃
(c) Starch sol
(d) Gold sol

Question. Which of the following has least flocculating value for positive sol?
(a) Cl^–
(b) SO₄^2–
(c) PO₄^3–
(d) [Fe(CN)₆]^4–

Case IV : Read the passage given below and answer the following questions.

Adsorption depends on the nature of the adsorbent. The rough solid surface has more number of pores and adsorb more number of gases than the smooth surface. Most common adsorbents are silica gel, activated charcoal. The extent of adsorption also depends on the surface area of the solid. Specific surface area of an adsorbent is the surface area available for adsorption per gram of the adsorbent. The greater the surface area of the solid, the greater would be the adsorption. Charcoal is a more effective adsorbent than solid wood. Desorption is a process of removing an adsorbed substance from a surface on which it is absorbed.
Physisorption is non-specific and any gas can be adsorbed. But the gases which are easily liquefiable (e.g., NH₃, HCl, CO₂) are adsorbed at a faster rate and to a large extent than the gases which are difficult to liquefy (e.g., H₂, O₂, N₂). It depends on the critical temperature. Higher the critical temperature of a gas, more easily liquefiable the gas is and more is the rate of adsorption. Chemisorption is specific in nature. Therefore, only those gases can be adsorbed which are capable of forming chemical bonds with the adsorbent.

Question. Which of the following statements regarding the physical adsorption of a gas on surface of solid is not correct?
(a) On increasing temperature, adsorption increases continuously.
(b) Enthalpy changes are negative.
(c) It is non-specific in nature.
(d) It is reversible in nature.

Question. Select the incorrect statement among the following.
(a) Physical adsorption is favourable at low temperature and chemisorption is favourable at high temperature.
(b) In physisorption heat of adsorption lies between 20-40 kJ mol^–1 while in chemisorption it lies between 80-240 kJ mol^–1.
(c) Chemisorption is irreversible and physisorption is reversible.
(d) Magnitude of chemisorption decreases with rise in temperature while physisorption increases with rise in temperature.

Question. At the same temperature and pressure,select the correct order of adsorption of the following gases on the same mass of charcoal.
(a) SO₂ > CH₄ > H₂
(b) CH₄ < SO2 < H₂
(c) H₂ > CH₄ > SO₂
(d) CH₄ < H₂ < SO₂

Question. Select the correct statement regarding desorption of gases on solid.
(a) It is done by cooling or by increasing the pressure applied.
(b) It is done by cooling or by reducing the pressure applied.
(c) It is done by heating or by reducing the pressure applied.
(d) It is done by heating or by increasing the pressure applied.

Question. Select the correct option among the following when adsorption of a gas on solid metal surface is spontaneous and exothermic.
(a) DS increases.
(b) DS decreases.
(c) DG increases.
(d) DH increases.

VERY SHORT ANSWER TYPE QUESTIONS

Question. Why are adsorbate particles attracted and retained on the surface of adsorbent ?
Answer. The unbalanced forces of the adsorbent are responsible for attracting adsorbate particles at adsorbent surface.

Question. How is lake test for aluminium ion based upon adsorption ?
Answer. Al₂O₃.xH₂O has the capacity to adsorb the colour of blue litmus from the solution.

Question. Mention the two conditions for the formation of micelles.
Answer. CMC and Tk.

Question.“Chemisorption is highly specific.” Illustrate with an example.
Answer. As it involves chemical bonding between adsorbent and adsorbate.

Question.Gelatin is generally added to ice-cream. Why ?
Answer. Ice-cream is water in oil type emulsion and gelatin acts as emulsifier.

Question. State the sign of entropy change involved when the molecules of a substance get adsorbed on a solid surface.
Answer.: DS = − ve

Question. Mention one shape selective catalyst used to convert alcohol directly into gasoline.
Answer. ZSM-5

Question. 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.
Answer.(a) Finely divided Fe/FeO, MO as promoter.
(b) Pt (Platinised asbestos)

Question. Why does a gas mixed with another gas not form a colloidal system ?
Answer. Gaseous mixture is homogeneous.

Question.Which group elements show maximum catalytic activity for hydrogenation reactions ?
Answer. 7-9 group elements.

Question. “Adsorbents in finely divided form are more effective.” Why ?
Answer. Due to their more surface area in finely divided form.

Question. Why gas masks are used by miners in coal mines while working ?
Answer. To absorb poisonous gases.

Question. Name two compounds used as adsorbent for controlling humidity.
Answer. Silica gel, Alumina gel

Question. Write the chemical reaction involved in the preparation of sulphur sol.
Answer.

Question.. How is Brownian movement responsible for the stability of sols ?
Answer. Stirring effect due to Brownian movement does not allow the particles to settle down.

Question.Explain the terms sorption and desorption.
Answer. Sorption is used to describe the process when adsorption and absorption take place simultaneously.
Desorption : Removal of adsorbate from the surface of adsorbent.

Question. Which of the following is more effective in coagulating positively charged hydrated ferric oxide sol : (i) KCl, (ii) CaSO₄, (iii) K₃[Fe(CN)₆] ?
Answer. K₃[Fe(CN)₆]

Question. What are the physical states of dispersed phase and dispersion medium in foam rubber ?
Answer. Dispersed phase : Gas; Dispersion medium : Solid

Question. Why do colloidal particles show Brownian movement ?
Answer. Due to unbalanced bombardment of the dispersed phase particles by the molecules of the dispersion medium.

Question. What are the optimum temperature and pH at which enzymes are highly active ?
Answer. Temperature 298-310 K and pH 5 to 7

Question. Why does sky appear blue to us ?
Answer. Due to scattering of blue light by dust particles and water suspended in air.

Question. ‘Generally high temperature is favourable for chemisorption.’ Why ?
Answer. To provide energy of activation.

Question. What happens when hydrated ferric oxide and arsenious sulphide sols are mixed in almost equal proportions ?
Answer. Mutual precipitation/coagulation took place.

Question. What is the composition of colloidion solution ?
Answer. 4% solution of nitrocellulose in a mixture of alcohol and ether.