CBSE 12th Standard Chemistry Subject Surface Chemistry Chapter Case Study Questions With Solution 2021
QB365 Provides the updated CASE Study Questions for Class 12 , and also provide the detail solution for each and every case study questions . Case study questions are latest updated question pattern from NCERT, QB365 will helps to get more marks in Exams
QB365 - Question Bank Software
CBSE 12th Standard Chemistry Subject Surface Chemistry Case Study Questions With Solution 2021
12th Standard CBSE
-
Reg.No. :
Chemistry
-
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.
The following questions are multiple choice questions. Choose the most appropriate answer :
(i) Select the correct statement regarding desorption.(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. (ii) 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 (iii) 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) Hz > CH4 > SO2 (d) CH4 < H2 < SO2 (iv) Select the incorrect statement among the following.
(a) Physical adsorption occurs at a low temperature and chemisorption occurs at all temperature (b) In physisorption heat of adsorption is low while in chemisorption it is high (c) Chemisorption is irreversible and physisorption is reversible (d) Magnitude of chemisorption decreases with rise in temperature while physisorption increases with rise in temperature. -
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 = kP1/n (was originally put forward by Freundlich and is known as Freundlich adsorption isotherm).
The following questions are multiple choice questions. Choose the most appropriate answer :
(i) According to Freundlich adsorption isotherm, which of the following is correct?(a) \(\frac{x}{m} \propto P^{0}\) (b) \(\frac{x}{m} \propto P^{1}\) (c) \(\frac{x}{m} \propto P^{1 / n}\) (d) All the above are correct for different range of pressure (ii) In the Freundlich adsorption isotherm equation
\(\log \frac{x}{m}=\log k+\frac{1}{n} \log p\) ,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. (iii) Plot of log xlm 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) 1g (b) 2g (c) 3g (d) 5g (iv) In the plot of log \(\frac{x}{m}\) vs log p for an adsorption, a straight line inclined at an angle of \(\theta=14.04^{\circ}\) 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 -
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 AS2 S3 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 \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}\)\(\mathrm{SO}_{4}^{2-}\) and Cl- is of the order,\(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}>\mathrm{SO}_{4}^{2-}>\mathrm{Cl}^{-}\) . 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.
The following questions are multiple choice questions. Choose the most appropriate answer:
(i) The gold number of four protective colloids A, B, C and Dare 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 > (ii) Which of the following has least flocculating value for positive sol?
(a) Cl- (b) \(\mathrm{SO}_{4}^{2-}\) (c) \(\mathrm{PO}_{4}^{3-}\) (d) [Fe(CN6)4- (iii) Which of the following colloidal solutions is positively charged?
(a) TiO2 (b) AS2 S3 (c) Blood (d) Gold sol (iv) The coagulation value in millimoles per litre of electrolytes used for the coagulation of As2 S3 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 -
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.
The following questions are multiple choice questions.Choose the most appropriate answer:
(i) In physisorption process, the attractive forces between adsorbate and adsorbent are(a) covalent bonds (b) ionic bonds (c) van der Waals' force (d) H-bonds (ii) Which of the following graph represents the variation of physical adsorption with temperature?
(iii) 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 (iv) 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. -
Read the passage given below and answer the following questions :
Colloidal particles carry either positive or negative charge. The nature of this charge is the same on all the dispersed particles in a given colloidal solution and may be either positive or negative. When two or more ions are present in the dispersion medium, preferential adsorption of the ion common to the colloidal particles usually takes place. When KI solution is added to the AgNO3 solution till KI is in excess, the precipitated silver iodide adsorbs iodide ions from the dispersion medium, and negatively charged colloidal solution results. If the colloidal sol of AgI is prepared by adding AgNO3 solution to KI solution till AgNO3 is in slight excess, Ag+ ions will be adsorbed giving positive charge to the colloidal particles. The combination of the two layers of opposite charges around the colloidal particles is called Helmholtz electrical double layer. The presence of equal and similar charges on colloidal particles is largely responsible for providing stability to the colloidal solution.
In these questions (i-iv), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.(a) Assertion and reason both are correct statements and reason is correct explanation for assertion. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion. (c) Assertion is correct statement but reason is wrong statement (d) Assertion is wrong statement but reason is correct statement. (i) Assertion : The presence of electric charge on colloidal particles is indicated by electrophoresis.
Reason : Lyophilic sols, in contrast to lyophobic sols are easily coagulated on addition of small amounts of electrolytes.
(ii) Assertion : Gold number is a measure of protective action by a lyophilic colloid on a lyophobic colloid.
Reason : Zeta potential (or electrokinetic potential) is the potential difference between fixed charged layer and the diffused layer having opposite charge.
(iii) Assertion: The presence of equal and similar charges on colloidal particles islargely responsible in providing stability to the colloidal solution.
Reason : The repulsive forces between charged particles having the same charge prevent them from aggregating and provide stability.
(iv) Assertion: When FeCl3 is added to an excess of hot water, a positively charged sol of hydrated ferric oxide is formed.
Reason : When ferric chloride is added to NaOH solution a negatively charged sol is obtained due to adsorption of OH- ions. -
Read the passage given below and answer the following questions :
A colloid is a heterogeneous system in which one substance is dispersed as very fine particles (called dispersed phase) in another substance (called dispersion medium). A colloid is classified on the basis of various criteria. Depending upon the nature of the interaction between the dispersed phase and the dispersion medium, colloidal sols are divided into two categories, viz., lyophilic and lyophobic sols. Depending upon whether the dispersed phase and the dispersion medium are solids, liquids or gases, the most common division are sols (solids in liquids), gels (liquids in solids) and emulsion (liquids in liquids). Depending upon the type of particles of the dispersed phase, these are of three types, multimolecular colloids, macromolecular colloids and associated colloids.
In these questions ( i-iv), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices(a) Assertion and reason both are correct statements and reason is correct explanation for assertion. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion (c) Assertion is correct statement but reason is wrong statement (d) Assertion is wrong statement but reason is correct statement. (i) Assertion: The range of diameters of the colloidal particles is between 1 and 1000 nm.
Reason : Colloidal particles are larger than the particles of true solution, but smaller enough to remain suspended
(ii) Assertion: Colloid is a heterogeneous system.
Reason: Colloidal particles have an enormous surface area per gram as a result of their small size.
(iii) Assertion: Fire fighting foams, used at emergency airplane landing is a colloidal system.
Reason: Gold sol is a multimolecular colloid.
(iv) Assertion: Gel on standing exudes small amounts ofliquid. This phenomenon is known as syneresis.
Reason : A colloidal solution of Fe(OH)3 in water is a hydrophobic colloid.
*****************************************
CBSE 12th Standard Chemistry Subject Surface Chemistry Case Study Questions With Solution 2021 Answer Keys
-
(i) (c) : Desorption is done by heating or by reducing the pressure applied.
(ii) (a) : Physisorption is exothermic in nature. Therefore, according to Le Chatelier's principle, it occurs readily at low temperature and decreases with increase in temperature. Bonds between surface and adsorbate are weak so when temperature is increased the bonds break easily, so rate will decrease on increasing temperature.
(iii) (a) : Higher the critical temperature of a gas, greater is the amount of gas adsorbed. Critical temperature (in Kelvin) of the gases :
\(\begin{array}{l} \mathrm{H}_{2}<\mathrm{CH}_{4}<\mathrm{SO}_{2} \\ 33.2 \quad 190.6 \quad 430.3 \end{array}\)
(iv) (d) : Chemisorption first increases with increase of temperature. Physisorption decreases with rise in temperature. -
(i) (d) : At low pressure \(\frac{x}{m} \propto P\)
At high pressure, \(\frac{x}{m} \propto P^{0}\)
In the intermediate range of pressure, \(\frac{x}{m} \propto P^{\frac{1}{n}}\)
(ii) (a)
In \(\frac{x}{m}=\ln k+\frac{1}{n} \ln P ; \quad \text { slope }=\frac{1}{n}=0\)
Thus, \(\frac{x}{m}=k P^{0}\)
(iii) (d) : According to Freundlich equation
\(\log \left(\frac{x}{m}\right)=\log k+\frac{1}{n} \log P\)
\(\therefore\) Plot oflog xlm vs log P is linear with slope = l/n and intercept = log k
Thus, \(\frac{1}{n}=\tan \theta=\tan 45^{\circ}=1 \text { or } n=1\)
At P = 0.5 atm and k = 10
\(\frac{x}{m}=k P^{1 / n}\)
\(\frac{x}{m}=10 \times(0.5)^{1}=5 \quad \therefore x=5 \mathrm{~g}\)
(iv) (c) : Plot of \(\log \frac{x}{m} v s \log P\) is a straight line with slope = \(\frac{1}{n}\)
Also, \(\text { slope }=\tan \theta=\tan 14.04^{\circ}=0.25\)
\(\Rightarrow \frac{1}{n}=0.25 \text { or } n=4\) -
(i) (a) : Lesser is the gold number, greater is the protective power.
(ii) (d) : Charge of [Fe(CN)6]4- is highest, hence, it will be most effective for the coagulation of positive colloids. More is the coagulating power lesser will be the flocculating value.
(iii) (a)
(iv) (c) : Coagulation value is inversely proportional to their flocculating power. -
(i) (c) : In physisorption process, the attractive forces between adsorbate and adsorbent are van der Waals' forces.
(ii) (a)
(iii) (d)
(iv) (a) -
(i) (c) : Lyophilic sols are stable and do not coagulate easily.
(ii) (b) : Gold number gives a comparative idea of protective power of various lyophilic colloids on a lyophobic colloid. Zeta potential is the potential difference between fixed charged layer and the diffused layer having opposite charge.
(iii) (a)
(iv) (b) -
(i) (b)
(ii) (b) : A colloid is a heterogeneous system in which one substance is dispersed (dispersed phase) as very fine particles in another substance called dispersion medium.
(iii) (b) : Gold sol is a multimolecular colloid since large number of molecules are combined to form this.
(iv) (b) : Syneresis is the extraction or expulsion of a liquid from a gel. Colloidal solution of Fe(OH)3 in water is hydrophobic colloid.
