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ISC Class XII Sample / Model Paper 2025 : Mathematics

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HOSUR SAHODAYA SCHOOLS COMPLEX PRE-BOARD EXAMINATION (2024-25) SUBJECT: CHEMISTRY (043) SET 2 Class: XII Date: 14.12.24 Marks: 70 Time: 3 HRS General Instructions: Read the following instructions carefully. a) There are 33 questions in this question paper with internal choice. b) SECTION A consists of 16 multiple-choice questions carrying 1 mark each. c) SECTION B consists of 5 very short answer questions carrying 2 marks each. d) SECTION C consists of 7 short answer questions carrying 3 marks each. e) SECTION D consists of 2 case-based questions carrying 4 marks each. f) SECTION E consists of 3 long answer questions carrying 5 marks each g) All questions are compulsory. h) Use of log tables and calculators is not allowed PART- A Sl. No 1. M Question SECTION I The following questions are multiple-choice questions with one correct answer. Each question carries 1 mark. There is no internal choice in this section. Study the graph showing the boiling points of alcohols and identify the compounds: Liquids Boiling points X 65 Y 78 Z 97 W 117 1 a) W = Butanol, X = Methanol, Y = Ethanol, Z = Propanol b) Y = Ethanol, Z= Propanol, X = Methanol, W = Butanol c) X= Methanol, Y = Ethanol, Z = Propanol, W = Butanol d) Z = Propanol, X = Methanol, W = Butanol, Y = Ethanol 2. 1 Proportion of molecules with energy E The diagram shows the Boltzmann distribution of the energy of gaseous molecules at a particular temperature. Which statement is correct? a) If the temperature of the gas is raised the height of the maximum of the curve increases b) If the temperature of the gas is raised the maximum of the curve moves to the right c) The length of the line labeled X shows the activation energy for the reaction d) The length of the line labeled Y shows the enthalpy change of the reaction Page 1 of 6 3. 4. 5. 6. 7. 8. 9. 10. 11. During a quiz competition, team A and team B have to answer a tie question on the characteristics of RNA.Their responses are as follows: Name Team Adrika A 1 Response The message for the synthesis of a particular protein is present only in the RNA Shaakho A The single stranded helix of RNA folds upon itself to form the secondary structure. Rounak B The C- 2 atom of the pentose sugar for a ribose nucleotide contains an OH group Ritama B Different RNA molecules of a cell are involves in the synthesis of proteins What is the expected result of the quize and why ? a) Team A wins the quiz as both the responses are correct. b) Team B wins the quiz as both the responses are correct. c) Team A loses the quiz as Adrika's response is incorrect. d) Team B loses the quiz as Rounak's response is incorrect. Hydrogen cyanide, HCN reacts with propanal CH3CH2CHO in the presence of potassium cyanide KCN. The mechanism for this reaction is a) Electrophilic substitution c)Nuclephilic substitution b) Electrophilic addition d)Nucleophilic addition Which of the following options give the correct arrangement of the atomic radii of the 3d, 4d, and 5d transition series of elements? a) atomic radii of 3d < atomic radii of 4d < atomic radii of 5d b) atomic radii of 3d < atomic radii of 4d atomic radii of 5d c) atomic radii of 3d atomic radii of 4d > atomic radii of 5d d) atomic radii of 3d > atomic radii of 4d > atomic radii of 5d Which is the correct increasing order of boiling points of the following compounds? 1-Iodobutane, , 1-Chlorobutane, Butane, 1-Bromobutane a)Butane < 1-Chlorobutane < 1-Bromobutane < 1-Iodobutane b)1-Iodobutane < 1-Bromobutane < 1-Chlorobutane < Butane c)Butane < 1-Iodobutane < 1-Bromobutane < 1-Chlorobutane d)Butane < 1-Chlorobutane < 1-Iodobutane < 1-Bromobutane 1 1 1 In nucleic acids, the sequence is: a) Sugar - phosphate - Base b)Base - phosphate - sugar c) Phosphate - sugar - base d) Sugar - base phosphate In which of the following ions, number of unpaired electron is zero? a ) Fe++ (Z = 26) b) Zn++ (Z = 30) c) Cr++ (Z = 24) d) Cu++ (Z = 29) 1 Which of the following will not show geometrical isomerism? a) [Cr(NH3)4Cl2] Cl b) [(Co(NH3)5NO2]Cl2 c) [Co(en)2Cl2]Cl d) [Pt(NH3)2Cl2] The bad smelling substance formed by the action of alcoholic caustic potash on chloroform and aniline is: a) Acetic acid b) Acetone c) Methanol d) Methylamine A + B + dil NaOH 1,3-diphenyl prop-2-en-1-one Identify A and B a) A = 1-phenylethanal, B = acetophenone b) A = benzophenone, B = formaldehyde c) A = benzaldehyde, B = acetophenone d) A = benzophenone, B = acetophenone 1 1 1 1 Page 2 of 6 12. 13. 14. Correct formulae of tetraamine chloronitroplatinum (IV) sulphate can be written as a) [Pt( 3)4 (ONO) Cl]SO4 b) [Pt(NH3)4Cl2NO2]2 c) [Pt(NH3)4 (NO2) Cl]SO4 d) [PtCl(ONO)NH3(SO4)] Blood cells retain their normal shape in solution which are: a) hypotonic to blood b) isotonic to blood c) hypertonic to blood d) equinormal to blood In these questions (14,15,16), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices. Assertion (A) : Amines being basic in nature react with acids to form salts Reason (R) : Aromatic amines are stronger bases than ammonia (a) Both Assertion and Reason are correct and Reason is a correct explanation of the Assertion. (b) Both Assertion and Reason are correct but Reason is not the a correct explanation of the Assertion. (c) Assertion is correct but Reason is incorrect. (d) Both the Assertion and Reason are incorrect. 15. 16. 17. 18. 19. 20. 21. 1 1 1 1 Assertion: KCl, NaCl, and NH4Cl cannot be used in the salt bridge of a cell containing silver. Reason : A salt bridge contains a concentrated solution of an inert electrolyte like KCl, KNO3,K2SO4 or a solidified solution of such an electrolyte in agar-agar and gelatine. a)Both Assertion and Reason are true but Reason is not the correct explanation of Assertion. b)Both Assertion and Reason are true and Reason is the correct explanation of Assertion. c)Assertion is false but Reason is true. d)Assertion is true but Reason is false. Assertion(A): An ether is more volatile than an alcohol of comparable molecular mass. Reason (R): Ethers are polar in nature. (a) Both Assertion and Reason are correct and Reason is a correct explanation of the Assertion. (b) Both Assertion and Reason are correct but Reason is not the a correct explanation of the Assertion. (c) Assertion is correct but Reason is incorrect. (d) Both the Assertion and Reason are incorrect. SECTION B This section contains 5 questions with internal choice in one question. The followingquestions are very short answer types and carry 2 marks each. Conductivity of 0.00241 M acetic acid is 7.896 x 10-5 S cm-1. Calculate its molar conductivity. The following compounds are given to you : 2-Bromopentane, 2-Bromo-2-methylbutane, 1-Bromopentane i)Which one of the compounds, given above, is more reactive towards SN2 reaction? (1) ii)Which one of the compounds given above, is more reactive towards -elimination reaction? (1) Arrange the following compounds in increasing order of their property as indicated : (i)CH3COCH3, C6H5COCH3, CH3CHO (1) (reactivity towards nucleophilic addition reaction) (ii)Cl CH2 COOH, F CH2 COOH, CH3 COOH (acidic character) (1) Giving a suitable example for each, explain the following : (i) Linkage isomerism(1) (ii)Ambidentate ligand(1) i. Sketch the zwitter ionic form of -amino acetic acid. (1) ii. What type of linkage holds together the monomers in DNA?(1) 1 2 2 2 2 2 Page 3 of 6 22. 23. 24. 25. 26. SECTION C This section contains 7 questions with internal choice in TWO questions. The following questions are short answer types and carry 3 marks each. Explain giving reasons: i) Cu 2+ salts are coloured while Zn 2+ are white. (1) ii)E0 value for the Mn 3+/ Mn2+ couple is much more positive than that for Cr3+/Cr2+ .(1) iii)There is a gradual decrease in the size of atoms with increasing atomic number in the series of Lanthanoids (1) ( OR) A metal ion Mn+ of the first transition series having d5 configuration combines with three didentate ligands. Assuming 0 < P: (i) Draw the crystal field energy level diagram for the 3d orbital of this complex.(1) (ii) What is the hybridisation of Mn+ in this complex and why?(1) (iii) Name the type of isomerism exhibited by this complex. (1) 3 What happens when D glucose is treated with the following reagents i) HI ii)Bromine water iii)HNO3 (Or) Write the mechanism involved in synthesis of alcohol from alkene i)Explain positive and negative deviations of Raoult s law with diagrams how is the sign of H related to it ? (2) ii) Give examples for each case. (1) 3 There are 5 reagent bottles containing NaNO2, HCl, Phenol, Aniline and NaOH separately in them. The teacher asked Amit to make an orange dye using suitable chemicals out of the five reagents given. (a)Write the chemical equations and the conditions for the steps involved in the preparation of the orange dye. (1 ) (b) Name the type of reaction of the step in which phenol reacts. (1 ) Abhisrija arranged two setups P and Q as shown below. 3 3 3 Both experiments are carried out at 25 C. (a) Name the current carriers in setup P and Q. (1) (b) What is the effect of an increase in temperature on the conductivity of NaCl solution and Cu wire? (1) (c)What happens to the chemical composition of NaCl and Cu wire when current is passed through both setups for a prolonged period of time?. (1) 27. i) a)Arrange the following compounds in an increasing order of basic strengths in their aqueous solutions Explain the reason: NH3, CH3NH2, (CH3)2NH, (CH3)3N (1 ) b)Out of CH3 NH2 and (CH3)3N, which one has higher boiling point?Why? (1 ) (OR) ii) a)Bromo butane is optically active. Explain the stereo-chemical aspect of SN2 reaction of 2-Bromobutane with OH- ions. (2) 3 Page 4 of 6 b)Write the reaction involved in the following : (1) 1.Williamson ether synthesis 2. Finkelstein reaction 28. i) Derive an expression for Integrated rate expression for rate constant of a first order reaction ? (2) ii)Draw the graph between ln[a] vs Time for first order find the slope and intercept. (1) SECTION D The following questions are case-based questions. Each question has an internal choice and carries 4 (1+1+2) marks each. Read the passage carefully and answer the questions that follow. 29. The rate law for a chemical reaction relates the reaction rate with the concentrations or partial pressures of the reactants. For a general reaction aA + bB------> C with no intermediate steps in its reaction mechanism, meaning that it is an elementary reaction, the rate law is given by r = k [A]x [B]y , where [A] and [B] express the concentrations of A and B in moles per litre. Exponents x and y vary for each reaction and are determined experimentally. The value of k varies with conditions that affect reaction rate, such as temperature, pressure, surface area, etc. The sum of these exponents is known as the overall reaction order. A zero-order reaction has a constant rate that is independent of the concentration of the reactants. A first-order reaction depends on the concentration of only one reactant. A reaction is said to be second order whenthe overall order is two. Once we have determined the order of the reaction, we can go back and plug in one set of our initial values and solve for k.In the context of the given passage, answer the following questions : Calculate the overall order of a reaction which has the following rate expression : Rate = k [A]1/2[B]3/2 Explain the term Half life period. i. ii. iii. 30. a)A first-order reaction takes 77.78 minutes for 50% completion. Calculate the time required for 30% completion of this reaction log 10 = 1, log 7 = 0.8450. ( OR) b)A first order reaction has a rate constant 1x 10-3 per sec. How long will 5g of this reactant take to reduce to 3 g? (log 3 = 0.4771; log 5 = 0.6990) CaseII: Phenols are acidic in nature. In substituted phenols, electron withdrawing groups such as NO2 , enhances acidic strength of phenol, if NO2 group is present at o- and p-position. It is due to effective delocalisation of negative charge on phenoxide ion. Electron releasing groups, such as alkyl groups, do not favour formation of phenoxide ions resulting in decrease in acid strength e.g. cresols are less acidic than phenols. The following table gives values of some Phenols and Ethanol. Compound Formula pKa o-Nitrophenol O -O2N C6 H4 OH 7.2 m-Nitrophenol m-O2 N C6 H4 OH 8.3 p-Nitrophenol p-O2 N C6 H4 OH 7.1 Phenol C6 H5 OH 10 o-Cresol 0 o-CH3 C6 H4 OH 10.2 m-Cresol m-CH3 C6 H4 OH 10.1 p-Cresol p-CH3 C6 H4 OH 10.2 Ethanol C2 H5 OH 15.9 3 1 1 2 Answer the following questions : i. From the above data, how many times phenol is more acidic than ethanol? 1 Page 5 of 6 ii. Out of phenols given in the table, which phenol is most acidic and why? 1 iii. a) Arrange the following in increasing order of acidic strength : phenol, o-nitro phenol, m-nitro phenol, p-nitro phenol, p-cresol (ii) Why are phenols less acidic than carboxylic acids? (OR) b) Arrange 2, 4, 6-trinitro phenol, 3, 5-dinitro phenol, 3-nitro phenol, phenol, propan-1-ol, 4-methyl phenol in increasing order of acidic character. (ii) Convert phenol to 2, 4, 6-trinitro phenol. 2 SECTION E The following questions are long answer types and carry 5 marks each. All questionshave internal choice. 31. 32. 33. A) i)The cell in which the following reaction occurs: 2Fe3+ (aq) + 2I (aq) -----> 2Fe2+ (aq) + I2(s) hasE0Cell = 0.236 Volt at 298K. Calculate the standard Gibbs energy of the cell reaction. (Given : 1 Faraday = 96,500 C mol) (3) ii)Describe working principle and application of lead storage battery. (2) (OR ) B)(I)Define the following terms: (2) (i) Ebullioscopic constant (ii) reverse osmosis (ii) A 5% solution (by mass) of cane sugar in water has freezing point of 271 K. Calculate the freezing point of 5% glucose in water if freezing point of pure water is 273.15 K. (3) 2+ 2+ i) Explain[CO(NH3)6] is an inner orbital complex.whereas [Ni(NH3)6] is an outer orbital complex.(3) ii) Draw figure to show the splitting of d-orbitals in an octahedral crystal field. (2) (OR) i) Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing pH on a solution of potassium dichromate? (3) ii) Actinoid contraction is greater from element to element than lanthanoid contraction. (2) I)A)Distinguish with a suitable chemical test : (2) (1) CH3COCH2CH3 and CH3CH2CH2CHO (2) primary,secondary,tertiary amine B) An alkene with molecular formula C5H10 on ozonolysis gives a mixture of two compounds B and C. Compound B gives a positive Fehling test and also reacts with iodine and NaOH solution Compound C does not give Feling solution test but forms Iodoform. Identify the compounds A,B, C. Write the reactions involved. (3) (OR) II)A)An organic compound (A) with molecular formula C6H7N on treatment with NaNO2 and HCl forms a compound (B), compound (B), on heating with CuCl2 and produces a compound(C) and on reacting with another molecule of C in presence of sodium and dry ether forms a compound (D). a)Write the reactions involved and structures of (A), (B), (C), and (D). b)Mention the name of reactions A-->B and C-->D 5 B) Explain briefly : (i) wolf kishner reduction ii) Aldol condensation 2 5 3 *** Page 6 of 6

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