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CBSE, Class XII Chemistry, Sample Paper 1, Term 2 – 2021 - 22, Time: 2 Hours, Total marks: 35, _________________________________________________________________________________________________________, General Instructions:,  There are 12 questions in the question paper with the internal choice.,  Section A: Q. No. 1 to 3 are very short questions carrying 2 marks each.,  Section B: Q. No. 4 to 11 are short answer questions carrying 3 marks each.,  Section C: Q. No. 12 is case based question carrying 5 marks.,  All questions are compulsory,  Use of calculators and log tables is not permitted., _________________________________________________________________________________________________________, , Section A, 1. What is Etard Reaction?, 2. The rates of a reaction starting with initial concentrations 2.0 × 10−3 M and 1.0 × 10−3 M are, equal to 2.40 × 10−4 M s−1 and 0.60 × 10−4 M s−1, respectively. Calculate the order of the, reaction with respect to the reactant and also the rate constant., 3. Arrange the following compounds in the increasing order of their reactivity in nucleophilic, addition reactions., (a) Ethanal, Propanal, Propanone, Butanone, (b) Benzaldehyde, p-Tolualdehyde, p-Nitrobenzaldehyde, Acetophenone, , Section B, 4. Account for the following:, (a) Electrophilic substitution in case of aromatic amines takes place more readily than, benzene., (b) CH3CONH2 is a weaker base than CH3CH2NH2., (c) Nitrocompounds have higher boiling points than hydrocarbons having almost same, molecular mass., 5., (a) Calculate number of unpaired electrons in complex [Ni(H2O)2(NH3)4]2+ ., (b) What type of isomerism is present in [Pt(NH3)4Cl2]Br2 and [Pt(NH3)4Br2]Cl2., (c) What is the geometry of Ferrocyanide ion?, 6., (a) Name two transition elements which show +1 oxidation state., (b) Name the transition element which does not exhibit variable oxidation state., (c) Transition elements show catalytic properties. Why?

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OR, (a) Write the steps involved in the preparation of Na2CrO4 from chromite ore., (b) What is the effect of increasing pH on K2Cr2O7 solution?, (c) Draw the structure of dichromate ion indicating the bond angles and bond lengths., 7., (a) Ethanol reacts with acetic acid in the presence of conc. H2SO4 to give sweet-smelling, substance. Give the equation involved in the reaction., (b) Write a note on, (i) Rosenmund’s reduction, (ii) Hell–Volhard–Zelinsky reaction, 8. Explain the term with a suitable example:, (a) Alcosol, (b) Aerosol, (c) Hydrosol, 9. An organic compound with the molecular formula C9H10O forms 2, 4-DNP derivative,, reduces Tollens’ reagent and undergoes the Cannizzaro reaction. On vigorous oxidation, it, gives 1, 2-benzene carboxylic acid. Identify the compound., OR, (a) How will you convert acetaldehyde to the following compounds?, (i) But 2-enal (ii) But-2-enoic acid, (b) Write a chemical test to distinguish between propanal and propanone., 10. The rates of a reaction starting with initial concentrations 2.0 × 10−3 M and 1.0 × 10−3 M are, equal to 2.40 × 10−4 M s−1 and 0.60 × 10−4 M s−1, respectively. Calculate the order of the, reaction with respect to the reactant and also the rate constant., 11. Give reasons:, (a) The radius of Fe2+ (Z = 26) is less than that of Mn2+ (Z = 25)., (b) Chemistry of actinoids is more complicated than that of lanthanoids., (c) Cu+ ion is not stable in aqueous solutions., , Section C, 12. Leclanche cell is a primary cell. It consists of a cylindrical zinc container which acts as the, anode. A graphite rod surrounded by a paste of manganese dioxide acts as the cathode., These are in contact with a thick paste of ammonium chloride and zinc chloride which acts, as the electrolyte., (a) What is the reaction taking place at the anode?, (b) How much electricity in terms of F is produced by the oxidation of one mole of Zn?, (c) Why Leclanche cell is considered as the primary cell ?, (d) What are the uses of Leclanche cell ?, (e) Write the other example of primary cell?

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Solution, _________________________________________________________________________________________________________, , Section A, 1. This reaction involves direct oxidation of heterolytic or an aromatic methyl group to, an aldehyde using chromyl chloride., Example- Toluene can be oxidized to benzaldehyde., , 2., S u p p o s e r = k [A ], , x, , w h e r e x = o r d e r o f t h e r e a c t io n ., , G iv e n is t h a t, 2 .4 0 X 1 0, , -4, , -3, , = k [ 2 .0 X 1 0 ], , x, , ( E q .1 ), , and, -4, , -3, , ( 0 .6 0 X 1 0 ) = k [ 1 .0 X 1 0 ], , x, , ( E q .2 ), , D iv id in g e q u a t io n ( 1 ) b y ( 2 ) g iv e s, -4, , -4, , -3, , -3, , ( 2 .4 0 X 1 0 ) / ( 0 .6 0 X 1 0 ) = [ ( 2 .0 X 1 0 ) / ( 1 .0 X 1 0 ) ], Or, x, , 2 =4= 2, , 2, , T h e r e fo r e ,, x=2, T h e r a t e la w is, 2, , R = k [ A ] a n d o r d e r o f r e a c t io n = 2, T h e rate co n stan t, k=, , =, , r, [A ], , 2, , 2 .4 0 X 1 0, -3, , -4, , ( 2 .0 X 1 0 ), , = 60 m ol, , -1, , 2, , Ls, , -1, , x

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3., (a) Butanone < Propanone < Propanal < Ethanal, (b) Acetophenone < p-Tolualdehyde < Benzaldehyde < p-nitrobenzaldehyde, , Section B, 4., (a) Due to resonance, the electrons on the N-atom in aniline are delocalized over the, benzene ring. As a result, the electron density on the benzene ring increases as, compared to benzene itself. In other words, aniline gets activated and hence, electrophilic substitution occurs more readily in aniline., (b) The lone pair of electrons on nitrogen interacts with oxygen atom due to, resonance. Hence, the lone pair of electrons on nitrogen is less available for, donation, which makes it less basic. While such mechanisms are not present in, CH3CH2NH2., (c) Nitro compounds are highly polar in nature, therefore, there is strong electrostatic,, attraction between nitrogen and oxygen atoms of a nitro group. As a result, a large, amount of energy is requried to break th nitrogen and oxygen nonds. Hence, nitro, comupounds have high boiling points in comarison with other comopounds., 5., (a) Electronic configuration of Ni+2= 1s2 2s2 2p6 3s2 3p6 3d8, So, Number of unpaired electrons =2, (b) [Pt(NH3)4Cl2]Br2 and [Pt(NH3)4Br2]Cl2 are types of ionisation isomers., (c) Ferrocyanide ion, i.e. [Fe(CN)6]4- is a type of octahedral complex., 6., (a) Au and Hg can show +1 oxidation state., (b) Scandium, (c) Transition elements exhibit variable oxidation state and can form complexes., OR, (a) 4FeCr2O4 + 8Na2CO3 + 7O2  8Na2CrO4 + 2Fe2O3+8CO2, (b) On increasing pH, the solution turns yellow due to the formation of chromate ion., (c) Cr2O72-+ 2 OH-  2CrO4 2- + H2O

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7., co n c. H2S O 4, ,  CH3COOCH2CH3 + H2O, (a) CH3CH2OH + CH3COOH      , (b), (i) In Rosenmund’s reaction, acid chlorides are subjected to catalytic, hydrogenation in the presence of Pd supported over BaSO4 to yield the, corresponding aldehyde. The catalyst is poisoned by S or quinoline., Pd,BaSO, , R C O C l + H 2    4,  RCHO + HCl, , (ii) In the Hell–Volhard–Zelinsky reaction, carboxylic acids react with chlorine or, , bromine in the presence of a small amount of P to give -halogenated, carboxylic acids. The reaction requires the presence of -hydrogen in the acid., ( i) X / R e d p h o s p h o r o u s, , R -C H 2 -C O O H   2 (,   , ii) H O, , R -C H -C O O H, , 2, , X, α -H a lo c a r b o x y lic a c id, ( X = C l, B r ), , 8., (a) Alcosol: A colloidal sol in which the dispersion medium is alcohol. Example:, Collodion, (b) Aerosol: When the dispersion medium is a gas and the dispersed phase is either, solid or liquid, the colloidal system is called an aerosol. Examples: Fog, cloud,, smoke, (c) Hydrosol: Colloids in water are called hydrosols. Examples: Milk, protein, 9., (i) The C:H ratio in the molecular formula suggests that the given compound is an, aromatic compound., (ii) Formation of 2, 4-DNP derivative indicates that the compound is an aldehyde or a, ketone., (iii) Since the compound reduces Tollens’ reagent, it must be an aldehyde and not a, ketone., (iv) Only aldehydes which do not contain an -hydrogen atom give the Cannizzaro, reaction. Thus, the aldehyde group should be directly attached to the benzene, ring. This implies that the ethyl group should be attached to benzaldehyde., (v) As vigorous oxidation of the aromatic aldehyde yields 1, 2-dicarboxylic acid, the, ethyl group must be present at the ortho position. Therefore, the compound is 2ethyl benzaldehyde.

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OR, (a), (i), , (ii) But 2-enal obtained in the above steps is treated with chlorine in CCl4 in the, dark and the product obtained is oxidised to dihaloacid which is further, dehalogenated to get but-2-enoic acid., , But-2-enoic acid, , (b) Propanal reduces Tollens’ reagent into silver mirror, while propanone does not, give this test., +, , C H 3 C H 2 C H O + 2  A g  N H 3   + 3 O H -    C H 3 C H 2 C O O - + 2 A g + 2 H 2 O + 4 N H 3, 2 , , P ro p an al, , 10., , T o lle n 's r e a g e n t

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11., (a) It is because the effective nuclear charge is more in Fe2+ than in Mn2+., (b) In actinoids, energy of 5f, 6d and 7s is comparable, and therefore, they show high, oxidation states and their chemistry is more complicated. All of them are, radioactive., (c) Due to low charge density, Cu+ has low enthalpy of hydration. Cu+ in aqueous, solution undergoes disproportionation., 2Cu+ (aq) → Cu2+ (aq) + Cu (s), The EӨ value for this is positive and the reaction is favourable., , Section C, 12., (a) Z n ( s )  Z n  2  2e , (b) Two electrons are released by Zn. So, according to Faraday’s law, 1 mole of Zn, produces 2F electricity., (c) In Leclanche cell, the reaction occurs only once, and after use over a period of time,, the battery dies and cannot be used as the reaction is not reversed. So, it is, considered a primary cell., (d) Leclanche cells are used in a tape recorder, radio, flashlight, transistor etc., (e) Other example of primary cell is Mercury cell.