NBSE Question Papers Chemistry for Class 12

Class 12  Series NBSE/XII/2023  Code No. 043/12/1 Roll No.  Candidates must write the Code No. on the title page of the Answer sheet. l Please check that this question paper contains 8 pages. l Code number given on the right hand side of the question paper should be written on the title page of the Answer sheet. l Please check that this question paper contains 30 questions. l 15 minutes time has been allotted to read this question paper. CHEMISTRY Time Allowed : 3 Hours Maximum Marks : 70 General Instructions: (i) All questions are compulsory. (ii) Section-A : Question number 1 to 9 are objective type questions and carry 1 mark each. (iii) Section-B : Question number 10 to 16 are short answer questions and carry 2 marks each. (iv) Section-C : Question number 17 to 27 are also short answer questions and carry 3 marks each. (v) Section-D : Question number 28 to 29 are long answer questions and carry 5 marks each. (vi) Section-E : Question number 30 is case based question and carry 4 marks. (vi) There is no overall choice. However, an internal choice has been provided. You have to attempt only one of the choices in such questions. (vii) Use log table, if necessary. Use of calculators is not allowed. NBSE 2023 1 P.T.O.

SECTION-A 1. Increasing the temperature of an aqueous solution will cause 1 (i) Increase in Molarity 1 (ii) Increase in Molality 1 (iii) Decrease in Molarity 1 (iv) Decrease in Molality 1 2. Phenol is more acidic than ethanol because (i) Ethoxide ion is more stable than Phenoxide ion. Column II (ii) Phenoxide ion is more stable than Ethoxide ion. (iii) Phenol undergoes electrophilic substitution reaction. (iv) Phenol undergoes protonation easily. 3. Complete the following analogy: time–1 : x : : mol lit –1 time–1 : y (i) x : unit of zero order, y : unit of first order (ii) x : unit of zero order, y : unit of pseudo first order (iii) x : unit of first order, y : unit of zero order (iv) x : unit of second order, y : unit of first order 4. Complete the following analogy Nickel-Cadmium Cell : A :: Lead storage Battery : B (i) A : Longer life, B : Shorter life (ii) A : Cheaper, B : Expensive (iii) A : Rechargeable, B : Non-Rechargeable (iv) A : Zinc Anode, B : Lead Anode 5. Match the items of Column I and Column II. Column I A. Diamond (1) short interval of time B. Instantaneous rate (2) ordinarily rate of conversion is imperceptible C. Average rate (3) long duration of time Codes: (i) A (1)  B (2)  C (3) (ii) A (2)  B (3)  C (1) (iii) A (3)  B (1)  C (2) (iv) A (2)  B (1)  C (3) N ote: In the question no. 6 and 7, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices. (i) Both assertion and reason are correct and the reason is correct explanation of assertion. (ii) Both assertion and reason are correct but reason does not explain assertion. (iii) Assertion is correct but reason is incorrect. (iv) Assertion is incorrect but reason is correct. NBSE 2023 2

6. Assertion: Relative lowering in vapour pressure is a colligative property. 1 Reason: Relative lowering in vapour pressure depends upon mole fraction of pure solvent. 7. Assertion: ECell should have a positive value for the cell to function. 1 Reason: Ecathode < Eanode 8. Out of chlorobenzene and cyclohexyl chloride, which one is more reactive towards nucleophilic substitution reaction and why? 1 OR Write one stereochemical difference between SN1 and SN2 reactions. 9. Among lanthanides, Ln (III) compounds are more predominant. However, occasionally in solutions or in solid compounds, +2 and +4 ions are also seen. Explain. 1 SECTION-B 10. Define order of reaction. Predict the order of reaction in the given graphs: 2 (i) (ii) Where [R]O is the initial concentration of reactant and t1/2 is half-life. 2 11 Give reasons: (i) An increase in temperature is observed on mixing chloroform and acetone. (ii) Aquatic animals are more comfortable in cold water than in warm water. 1 2. When FeCr2O4 is fused with Na2CO3 in the presence of air it gives a yellow solution of compound (A). Compound (A) on acidification gives compound (B). Compound (B) on reaction with KCl forms an orange coloured compound (C). An acidified solution of compound (C) oxidises Na2SO3 to (D). Identify (A), (B), (C) and (D). 2 1 3. Answer the following: 2 (i) Carbon tetrachloride is insoluble in water. Why? (ii) Write about two industrial applications of chloroform and freons. OR Explain why vinyl halide is less reactive while allyl halide is more reactive than alkyl halides? 1 4. Define the following terms with a suitable example of each: 2 (i) Polydentate ligand (ii) Homoleptic complex OR Using IUPAC norms, write the formulae for the following complexes: (i) Potassium tri(oxalato) chromate(III) (ii) Hexaaquamanganese(II) sulphate 15. (i) Although both [NiCl4]2– and [Ni(CO)4] have sp3 hybridisation yet [NiCl4]2– is paramagnetic and [Ni(CO)4] is diamagnetic. Give reason. (Atomic no. of Ni = 28)  2 NBSE 2023 3 P.T.O.

(ii) Write the electronic configuration of d5 on the basis of crystal field theory when (a) ∆o < P and (b) ∆o > P 1 6. Write structures of main compounds A and B in each of the following reactions: 2 (i)        (ii) SECTION-C 17. The following data were obtained for the reaction: A + 2B → C 3 Experiment [A]/M [B]/M Initial rate of formation of C /M min–1 (i) Find the order of reaction with 1 0.2 0.3 4.2 × 10–2 respect to A and B. 2 0.1 0.1 3 0.4 0.3 6.0 × 10–3 (ii) Write the rate law of overall 4 0.1 0.4 1.68 × 10–1 order of reaction. 2.40 × 10–2 (iii) Calculate the rate constant (k). 18. From analysis and molecular weight determination, the molecular formula of a compound (A) is found to be C3H7NO. The following information is given for this compound: 3 (i) On hydrolysis it gives an amine (B) and a carboxylic acid (C). (ii) Amine (B) reacts with benzene sulphonyl chloride and gives a product which is insoluble in aqueous sodium hydroxide solution. (iii) Acid (C) on reaction with Tollens’ reagent gives silver mirror test. What are the name and molecular structures of (A), (B) and (C)? Explain the reactions with the help of equations. 19. A solution containing 1.9 g per 100 mL of KCl (M = 74.5 g mol–1) is isotonic with a solution containing 3 g per 100 mL of urea (M = 60 g mol–1). Calculate the degree of dissociation of KCl solution. Assume that both the solutions have same temperature. 3 20. Two half cell reactions of an electrochemical cell are given as: 3 MnO4– (aq) + 8H+ (aq) + 5e– → Mn2+ + 4H2O(l) E° = +0.151V Sn2+(aq) → Sn4+(aq) + 2e– E° = + 0.15 V Construct the redox equation from the two half-cell reactions and predict if this reaction favours the formation of reactants or products as shown in the equation. 21. Give reasons for the following: 3 (i) Transition metals have high enthalpies of atomization. (ii) Manganese has lower melting point even though it has a higher number of unpaired electrons for bonding. (iii) Ce4+ is a strong oxidising agent. 2 2. Explain the following: 3 (i) Low spin octahedral complexes of nickel are unknown. (ii) p complexes are known for transition metals only. (iii) CO is strong ligand than NH3 for most of the metals. NBSE 2023 4

2 3. Complete the following reactions: 3 (i)  (ii)  (iii) OR How do you convert the following: (i) N-phenylethanamide to p-bromoaniline 3 (ii) Benzene diazonium chloride to nitrobenzene (iii) Benzoic acid to aniline 24. Give the reagent used to bring about the following transformations: (i) Pent -3-en-2-ol to pent -3-en-2-one (ii) But-1-yne to Butan-2-one (iii) p-nitrotoluene to p-nitrobenzaldehyde. OR Carry out the following conversions? (i) Acetone from ethanol 3 (ii) Methanal to ethanal (not more than 3 steps) 3 (iii) Propanal to propane 25. Among all the isomers of molecular formula C4H9Br, identify (i) the one isomer which is optically active. (ii) the one isomer which is highly reactive towards SN2. (iii) the two isomers which give same product on dehydrohalogenation with alcoholic KOH. 2 6. (i) Write the product when D-glucose reacts with Br2 (aq). (ii) What type of bonding provides stability to a-helix structure of protein? (iii) Name the vitamin whose deficiency causes pernicious anaemia. OR Define the following terms: (i) Invert sugar      3 (ii) Native protein      (iii) Nucleotide 27. (i) Give reasons: (a) Benzoic acid is a stronger acid than acetic acid. (b) Methanal is more reactive towards nucleophilic addition reaction than ethanal. (ii) Give a simple chemical test to distinguish between propanal and propanone. SECTION-D 2 8. (i) The conductivity of 0.001 mol L–1 acetic acid is 4.95 ×10–5 S cm–1. Calculate the dissociation constant if / o for acetic acid is 390.5 S cm2 mol–1. 5 m NBSE 2023 5 P.T.O.

(ii) Write Nernst equation for the reaction at 25°C: 2 Al (s) + 3 Cu2+ (aq) → 2 Al3+ (aq) + 3 Cu (s) (iii) What are secondary batteries? Give an example. OR (i) Represent the cell in which the following reaction takes place: 2 Al (s) + 3 Ni2+ (0.1 M) → 2Al3+ (0.01 M) + 3 Ni (s) Calculate its emf if E 0 = 1.41 V. cell (ii) H ow does molar conductivity vary with increase in concentration for strong electrolyte and weak electrolyte? How can you obtain limiting molar conductivity ( / o ) for weak electrolyte? m 29. (i) Give equations of the following reactions: 5 (a) Phenol is treated with conc. HNO3. (b) Propene is treated with B2H6 followed by H2O2/OH–. (c) Sodium t-butoxide is treated with CH3Cl. (ii) How will you distinguish between butan-1-ol and butan-2-ol? (iii) Arrange the following in increasing order of acidity: Phenol, ethanol, water OR (i) How can you obtain phenol from (a) Cumene, (b) Benzene sulphonic acid, (c) Benzene diazonium chloride? (ii) Write the structure of the major product obtained from dinitration of 3-methylphenol. (iii) Write the reaction involved in Kolbe’s reaction. SECTION-E 3 0. Carbohydrates are the main source of energy that is ingested by the human body (Caffall et al., 2009). Brain mainly utilizes the glucose. Red blood cells also use glucose only. Fiber in the diet is not digested by human body due to lack of cellulase enzyme. Glucose is the major energy source in the body. Glycogen is the storage form of glucose and glycogen is stored in skeletal muscles and liver. If glucose intake exceeds than it is utilized in the body then it is converted into fat. Riboses are utilized in formation of deoxyribonucleic acid (Hou et al., 2009). Carbohydrates are polyhydroxy alcohol with potentially active carbonyl group which may be aldehyde or keto group. Carbohydrates can be classified on the basis of carbon atom present in the carbohydrates. Carbohydrates are classified into four types monosaccharides, disaccharides, oligosaccharides, polysaccharides. Monosaccharides cannot be hydrolyzed further into simpler form. Disaccharides give two monosaccharides on hydrolysis. Polysaccharides may be homopolysaccharides and heteropolysaccharides. (Source: H.M. Asif, Muhammad Akram, Tariq Saeed, M. Ibrahim Khan, Naveed Akhtar, Riaz ur Rehman, S.M. Ali Shah, Khalil Ahmed, Ghazala Shaheen, 2011, Carbohydrates, International Research Journal of Biochemistry and Bioinformatics Vol. 1(1) pp. 001-005) 4 In these questions, 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. NBSE 2023 6

(i) Assertion : D (+)-Glucose is dextrorotatory in nature. Reason: ‘D’ represents its dextrorotatory nature. (ii) Assertion: In human system, starch can act as nutrient but cellulose does not. Reason: Human body does not contain enzyme to hydrolyse cellulose. (iii) Assertion: Glucose has an open structure. Reason: Glucose on reacting with HI gives n-hexane. (iv) Assertion: Sucrose is a non-reducing sugar. Reason: A free aldehyde group is present is sucrose. OR Assertion: Glycogen is called animal starch. Reason: Glycogen is stored in animal body. NBSE 2023 7 P.T.O.

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