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ISC Class XII Prelims 2025 : Chemistry (St. Stephens School, Dum Dum, Kolkata (Calcutta))

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08 Aratrikaa Dey
St. Stephen's School, Dum Dum, Kolkata (Calcutta)
X and XII Science

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St.Stephen's Schol- BumBum PRE- BOARD EXAMINATION 2024-25 Class: 12 Subject:- Chemistry Full marks:- 70 Time:-3 hours (Candidates are allowed an additional 15 minutes for only reading the paper. They must NOT start writing during this time.) This paper is divided into four sections -A, B.Cand D. Answer all questions. Section -Aconsists of one question having sub-parts of one mark each. Section -Bconsists of ten questions of two marks each. Section -Cconsists of seven questions of three each and SectionD consists of three questions of five marks marks each. Internal choices have been provided in one question each in Section B. Section C and Section D. Allwork, including rough work, should be done on the same sheet as, and adjacent to the rest of the answer. The intended marks for questions or parts of questions are given in brackets [ Balanced equations must be given wherever possible and diagrams where they are helpiul. when solving numerical problems, all essential work must be shown. working out problems, use the data: dm atmk'mo Gas constant R= In1.987 cal deg' moH a214 JK' following mot =0.0821 1latm = 1 dm atm =10124Earaday =96500 coulombs. Avogadr 's number r= 6.023x 1023 Section A (14marks) Qupstion 1 in the blanks by choosing the appropriate word(s) from those given in the [4x1] bracket. (Diamagnetic, Methanol, cathode. More Tn.less.Halogen, Carbon,C-X,C-C,triple, double,Anode,paramagnetic.) In a galvanic cell, electrons flow from connecting wires. to through the Haloalkenes undergo both nucleophilic and electrophilic reactions due to the presence of the bond and the atom. Para nitro acid than m-benzoic acid is nito benzoic acid. Ferricyanide ion is acid than 0- nitro benzoic acid but magnetic while ferrocyanide nature. (B) Selectand write the correct ion is alternative frofrom the choices given below. magnetic in [7x1] Cannizaro's reaction is given by: (a) CH,CHO ) An (b) HCHO (c) CH,CH,CHO excess of AgNO, 0s added to 100ml l of (ll1) aqua Would chromium be: chioride. The (d) (CH),CHCHO a 0.01M solution of dichlorotetra number of moles of AgCl precipitated (a) 0.03 (b) 0.01 (c) 0.001 (d) 0.002 Ai) Grystal field splitting energy (CFSE) for high spin d' octahedral complex is: (a) -1.6Dq (b) -1.2Dq (c) -0.8Dq (a) -0.6Dq (iv Liquid Aand Bform an ideal solution and Ahas higher forces IFX.andX,are the mole fraction of Ain the solution andintermolecular vapour in equilibrium, then : (a) X,/ X,=1 (b) X,X,>1 (0) X/ X,<1 () X,+X, =1 W) Lanthanide contraction is due to an increase in: (a) Shielding of 4f electrons (b) atomic number (c) effective nuclear charge (d) size of 4f orbital A) Assertion: [ Co(NH3)J is an inner orbital complex. Reason: [ Co(NH,)|] forms an octahedral complex. (a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion. (b) Both Assertion and Reason are true and Reason is not the correct explanation of Assertion. (c) Assertion is true but Reason is false. (d) Assertion is false but Reason is true. nAssertion: Ethanol can be distinguished from methanol using Reason: Ethanol has a methyl iodoform Test. group attached to a carbon-containing hydroxyl group. (a) Both Assertion and Reason are true and Reason is the correct texplanation of Assertion. (b) Both Assertion and Reason are true and Reason is not the correct explanation for Assertion (c) Assertion is true but Reason is false. (d) Assertion is false but Reason is true. o)Read the passage given below carefully and answer the questions that follow.[3) Nucleophilic substitution reactions are of two types; bimolecularThe(S1) depending molecules taking part insubstitution nucleophilic reaction. reactivity of alkyl halide towards S1 determining the rate of and SN2 various factors such as steric hindrance, stability of reaction depends on and polarity of solvent. S,2 or transition state intermediate reaction mechanism is favoured mostly halide then secondary and then tertiary, This order is reversed in theby primary alkyl reactions. case of SN1 Va) Which of the following is most reactive towards nucleophili substitution reaction? (1) CaHsCI (2) CH;=CHCI (3) CICH,CH=CH, ( CHCH=CH-CI Jo Tertiary butyl chloride undergoes hydrolysis by which mechanisn? is (erWhat the stereochemical outcome of the SN mechanism. reaction? Explain with Qdestion 2 Section B (20 marks) YArrange2-the following alcohols in order of decreasing butanol, and 1-butanol.activity towards Lucas reanent () There are bwo-NH,2-methyl-2-propanol groups in semicarbazide but only one is formation of semicarbazone. Explain. Involved in the poostion 3 Give a reason for each of the following. 121 c a stg redng aOert value of copper is postve. Queatlon 4 (21 foioing Gve balanced chemical the to oonyert Anne to 2.4,6 (0) lo Urotropine. equations Formaldehyde trnbromoaniine (21 Question 5 Complete the following equation. Cr0, + 14H' +6t (0) 2Cr0,+ 2H* (i) Qyestion 6 S (21 Write the cell reaction of a lead storaae battery when it is dischargeo. Can ED cell or G for a celil reaction ever be equal to zero? (2) 9destlon 7 Two compounds, D-2-chiorobutane and L-2-chlorobutane, other. are enantiomors of each Name one physical property that is: ( ) Same for D-2- chlorobutane and L-2-chlorobutane. Different for D-2- chlorobutane and L-2-chlorobutane. Questlon 8 () What happens when (write chemical reactions only) (a) Methoxybenzene reacts with HI (b) Methyl amine is react with Chloroform and alc. KOH. OR NaOH An organic compound (A) has a characteristic odour on treatment with it forms two compounds (B) and (C). Compound (B) has molecular formula CyH,0 which on oxidation give back (A). The compound (C) is a sodiurn salt of an acid. When (C) is treated with soda lime it yields an aromatic hydrocarbon (D). Deduce the struclures of (A), (B). (C) and (D). Questi n 9 (2) Hglycerine, CaH,0, and methyl alcohol, CH,OH ,are sold at the same price per kg. which would be cheaper for preparing an antifreeze solution for the radiator of an Butomobile? Qubstion 10 (CH,),C-0-CH, on and not with Hl gives reaction and CH,I explain. (CH, ) , C -oH Question 11 (CHshC- and CH,OH asthe(2) main products Give reason (21 metals are high. explain why of ent h al p i e s Transition elements show variable atomisation transition a to the of SECTION Question- 12 For a certain below. [3) chemical oxidation states why? C-21 MARKS reaction. variation in concentration In (R] vs. time (s) plot is given in R] T 1() For this V) Aii) reaction write ldraw: What is the order of the reaction? What are the units of the rate What does the slope of the constant K? above line indicate? Question 13 Arrange the following according to the instructions given in brackets. [31 Y ( Y CHsNH, C , H , C H, N H, C oH, N HCH, (i n creasi n g order of basi c st r engt h . ) CH,CH,COOH, CIC&,COOH, HCOOH, CsH,CH,COOH,FCH,COOH,CgioOH(increasing order of acidic strength) 4-chloronitrobenzene, 2-chloronitrobenzene. 24,6-trinitrochlorobenzene, 2,4- dinitrochlorobenzene.(increasing substitution.) Questlon 14 () order oftowards nucdeophilic [3] Name the final product of the hydrolysis of proteins. Enumerate the of chain structure.? cannot be explained by its open (i) reaclions D-glucose which (ii) What is the product obtained when D-glucose is treated with con. HNO,? Question 15 Ametal M(atomic mass 96) 9.18gm of this salt is dissolved in forma salt represented as [3] MF, On reaction with fluorine 374.38 K.What is the chemical 100gmof of water andit's boiling formula the salt.(K, =0.512K point determined to be kg/mol). Question 16 Identify the compounds A, Band C CH.COOH sQ2 [A] Poess [BoNHICI Qugston How 17 will you bring about the folowing conversions: (0) [3] (3] Ethanol to but-2 enal Aniline to Para bromo aniline. in Phenol to 2- hydroxybenzoic acid. OR Explain the mechanism of acid-catalysed dehydration of ethanol to yield the corresponding ether. Question 18 The rate constant for the first-order reaction is given by the equation: Log.K(s")= 14.34 - 1 25 x10' k/T (3) Given E zZn= V; ED SnSn -0.14V -0.76 = 1Faraday reduction of (6 How much 96500 C mol the complete for requ red in Mn? MnO, ions electricity present in Faradayf0.5is Msolutionto 50Oml of ORobtained when molar conductivity A, is plotted (a) The following curve is against the square root of Concentration vc along the y and x axis respectively for the two electrolytes Xand Y. mol AScm 400 200 X 0.2 0.4 C/(mol L)4 (1) What can you say about the nature of the two electrolytes? (2) Howdo youaccount for the increase in An for the electrolytes Xand Ywith dilution? (3) How can you determine n for these electrolytes? (b) The molar conductivity (Am) of a dilute solution of methanoic acid is 34,1 S cm/mol. Calculate its degree of dissociation, (Given A(H) =349.6 Scm/mol and A (HCO0) =54.6 Scm Imol)

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