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CBSE Class 12 Pre Board 2021 : Chemistry (Kendriya Vidyalaya (KV), Lucknow Region)

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KENDRIYA VIDYALAYA SANGATHAN LUCKNOW REGION PRE BOARD EXAMINATION 2020-21 CLASS- XII Subject Chemistry Time allowed : 3 Hrs Maximum Marks : 70 General Instructions :1.There are 33 questions in this question paper. All questions are compulsory. 2. Section A : Q.No. 1 to 2 are case-based questions having four MCQs or Reason Assertion type based Given passage each carrying 1 mark. Q. No. 3 to 16 are MCQs and Reason Assertion type questions carrying 1 mark each. 3. Section C : Q. No. 17 to 25 are short answer questions and carry 2 marks each. 4. Section D : Q. No. 26 to 30 are short answer questions and carry 3 marks each. 5. Section D : Q. No. 31 to 33 are long answer questions carrying 5 marks each. 6. There is no overall choice. However, internal choices have been provided. 7. Use of calculators and log tables is not permitted. 1 SECTION A (OBJECTIVE TYPE) Read the passage given below and answer the following questions: The d- block of the periodic table contains the elements of the groups 3-12 and are known as transition elements. In general, the electronic configuration of these elements is (n-1)d1-10ns1-2. The d orbitals of the penultimate energy level in their atoms receive electrons giving rise to the three rows of the transition metals i.e. 3d, 4d and 5d series. However, Zn, Cd and Hg are not regarded as transition elements. Transition elements exhibit certain characteristic properties like variable oxidation states, complex formation, formation of coloured ions and alloys, catalytic activity etc. Transition metals are hard (except Zn, Cd and Hg) and have a high melting point. The following questions are multiple choice questions. Choose the most appropriate answer: (i) Which transition metal of 3d series does not show variable oxidation states? (a) Cr (b) Ti (c) Sc (d) Fe (ii) Which of the following statement about transition element is not correct? (a) They show variable oxidation states. (b) They exhibit diamagnetic and paramagnetic properties. (c) All the ions are coloured. (d) They exhibit catalytic properties. (iii) The magnetic moment is associated with its spin angular momentum and orbital angular momentum. Spin only magnetic moment of Cr3+ ion is (a) 2.87 BM (b) 3.87 BM (c) 3.47 BM (d) 3.57 BM (iv) Which of the following has maximum number of unpaired d- electrons? (a) Mg2+ (b) Ti3+ (c) V3+ 4 (d) Fe3+ 2. The freezing point of a solution depends upon freezing points of solute and solvent. Solution freezes somewhere between these two values. The density of water increases when solute is added to water and thus it freezes at lower temperature. Freezing temperature of liquid with higher density would be lower. The higher density means the more difficult to freeze. Alcohol is volatile, also decreases the freezing point of water. Alcohol- water mixture has lower freezing point than pure water. Freezing point depression of all solutions is independent of the volatility of solute. (Reference: Chem. Educ.Res Pract. 2009, 10,273-280 The Journal is @Royal Society of Chemistry 2009) In these questions, a statement of assertion followed by a statement of reason is given. Choose the correct option 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. 4 (i) Assertion : Ethylene glycol is added to car radiators acts as antifreeze. Reason : Ethylene glycol lowers the freezing point of water. (ii) Assertion : If more and more solute is added to a solvent, the freezing point of the solution keeps on becoming higher and higher. Reason : Presence of large amount of solid solute does not allow the solution to freeze. (iii) Assertion : Greater the molal depression constant of the solvent used, lesser is the freezing point of the solution. Reason : Depression in freezing point depends upon the nature of the solvent. (iv) Assertion : Molecular mass of polymers cannot be calculated using boiling point or freezing point method. Reason : Polymers solutions do not possess a constant boiling point or freezing point. Or Assertion : 0.1 M solution of glucose has higher depression in freezing point than 0.1 M solution of urea. Reason : Kf for both glucose and urea solutions are same. Following questions (3-11) are multiple choice questions carrying 1mark each: 3. Which of the following is correct for spontaneity of a cell ? (a) G0 = -ve, E0cell = +ive (b) G0 = +ve, E0cell = 0 (c) G0 = -ve, E0cell = 0 (d) G0 = +ve, E0cell = -ive OR Which of the following solutions of KCl will have the highest value of specific conductance? (a) 0.5 M (b) 0.01 M 1 (c) 0.1 M (d) 1.0 M 4. The vapour pressure of a solvent is 20 mm Hg, whereas its dilute solution containing nonvolatile solute is 17 mm of Hg. The mole fraction of the solvent is (a) 0.60 (b) 0.40 0.85 (d) 0.15 1 OR 5. 6. 7. Which of the following mixtures will show a positive deviation from Raoult,s law ? (a) Methanol and water (b) Chloroform and acetone (c) Nitric acid and water (d) Phenol and aniline A metallic crystal crystallizes into a lattice containing a sequences of layers AB AB AB. A packing of spheres leaves out voids in the lattice. What is the percentage of volume of this lattice in empty space? (a) 74% (b) 26% (c) 50% (d) None of these On the basis of crystal field theory for d6 ion, if correct ? (a) t62geg0 (b) t42ge2g (c) 6 unpaired electrons (d) 4 unpaired electrons - D(+) glucose and -D(+) glucose are (a) geometrical isomers (b) enantiomers (c) anomers (d) optical isomers 0 1 > P, which of the following is 1 . 1 OR Which of the following is globular protein? (a) Keratin (b) Fibroin (c) Myosin (d) Albumin 8. 9. The coordination number of Co in the complex [Co(en)3]3+ is (a) 3 (b) 4 (c) 5 (d) 6 1 + 2 CH3-CH2-OH X, X is (a) No reaction (b) Yellow ppt of CHI3 (c) CH3CHO (d) CH3COCH3 1 10. 11. Ethylidene chloride is a/an _________ (a) vic-dihalide (b) gem-dihalide (c) allylic halide (d) vinylic halide. 4 2 CH3CH2-CO-NH2 X (a) CH3CH2CH2OH (b) CH3CH2OH (c) CH3OH (d) CH3CH2CH2N2+OH- 1 Y, where Y is 1 OR The correct IUPAC name for CH2=CHCH2NHCH3 is (a) Allylmethylamine (b) 2-amino-4-butene (c) 3-aminobut-1-ene (d) N-methylprop-2-en-1-amine 12. 13. 14. 15. 16. 17. 18. 19. 20. In the following questions (Q. No. 12-16), 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. Assertion: Stereochemical inversion takes place in SN2 mechanism. Reason: The intermediate carbocation is formed in SN2 Assertion: DNA has Thymine base which is not present in RNA. Reason: DNA helps in transfer of genetic characteristics. OR Assertion: Two strands in double strand helix structure of DNA are complementary to each other. Reason: Hydrogen bonds are formed between specific pair of bases. Assertion: Aromatic acids do not undergo Friedel-Crafts reaction. Reason: -COOH group is a m- directing group. Assertion: Alkyl halides are polar but insoluble in water. Reason: Alkyl halides have higher boiling points than alcohol. Assertion : O-O bond is weaker than S-S bond. Reason: There is more repulsion between lone pair in O-O bond than S-S bond due to small size of oxygen. SECTION B The following questions, Q. No. 17-25 are short answer type and carry 2 marks each. A metal crystallizes as face centred cubic lattice with edge length of 450 pm. Molar mass of metal is 50 gmol-1. Find the density of metal. State Henry,s law. Why is air diluted with helium in the tanks used by scuba divers ? OR Define osmotic pressure. Why do red blood cells shrink when placed in water containing less than 0.9% (mass/volume) salt ? The decomposition of NH3 on platinum surface is zero order reaction. What are the rates of production of N2 and H2 if k = 2.5 x 10-4 mol-1Ls-1. Write any two differences between order and molecularity of a reaction. 1 1 1 1 1 2 2 2 2 21. 22. 23. 24. 25. 26. 27. When a coordination compound CoCl3.6NH3 is mixed with AgNO3, 3 moles of AgCl are precipitated per mole of the compound. Write (i) Structural formula of the complex. (ii) IUPAC name of the complex. Write the final product(s) in each of the following reactions: (i) CH3-CH=CH-CH2OH (ii) C6H5-OH 3+ 2 + Complete the following reaction equation: (i) XeF2(s) + H2O(l) (ii) NaOH(cold & dil) + Cl2 OR Write balanced equations for the following : (i) SO2 gas is passed through an aqueous solution of Fe3+ salt (ii) XeF2 reacts with PF5 Explain the following with an example (i) Williamson synthesis (ii) Carbylamine reaction Give simple chemical test to distinguish between the following pairs of compounds (i) Propanal and Propanone (ii) Phenol and Benzoic acid SECTION C Q. No. 26-30 are short answer type II carrying 3 marks each Explain what is observed when (i) a beam of light is passed through a colloidal solution. (ii) an electrolyte is added to hydrated ferric oxide sol. (iii) electric current is passed through a colloidal sol. OR Define the following terms giving an example of each (i) Associated colloids (ii) lyophilic sols (iii) Zeta potential Give reason: (i) A transition metal exhibits the highest oxidation state in oxides and fluorides. (ii) The enthalpies of atomization of transition metals are high. (iii) Zr and Hf have nearly same atomic radii. 28. Arrange the following in the increasing order of- 29. (i) C2H5NH2, C6H5NHCH3, (C2H5) 2NH, C6H5NH2 (pkb values) (ii) C6H5NH2 , (C2H5) 2NH, C2H5NH2 (solubility in water) (iii) Aniline, p-nitroaniline, p-toluidine ( basic strength) Carry out the following conversions: (i) Propan-2-ol to propanone (ii) Phenol to benzoquinone (iii) Ethanol to ethanoic acid 30. 2 Define the following with an example (i) Monosaccharides (ii) Essential amino acids (iii) Denaturation of proteins 2 2 2 3 3 3 3 3 31. 32. 33. OR (a) Write the product obtained when D- glucose reacts with Br2 water. (b) What type of bonding stabilizes the - helix structure of proteins? (c) Name the linkage that joins the two nucleotides. Section-D (a) Calculate E0cell for the following reaction at 298K : 2Al (s) + 3Cu2+ (0.01M) 2Al3+ (0.01M) + 3Cu(s) Given : Ecell = 1.98 V (b) How does molar conductivity vary with increase in concentration for strong and weak electrolyte? How can limiting molar conductivity of a weak electrolyte be obtained? OR -1 (a) The conductivity of 0.001 mol L solution of CH3COOH is 3.905x 10-5 S cm -1. Calculate its molar conductivity and degree of dissociation ( ) Given 0 (H+)= 349.6 S cm2 mol-1 and 0 (CH3COO-) = 40.9 S cm2 mol-1 (b) Define electrochemical cell. What happens if external potential applied becomes greater than E0cell of electrochemical cell ? (a) Draw the structures of the following : (i) XeF4 (ii) BrF3 (b) Account for the following : (i) Iron on reaction with HCI forms FeCl2 and not FeCl3. (ii) HClO4 is a stronger acid than HClO. (iii) BiH3 is the strongest reducing agent amongst all the hydrides of group 15. OR (a) Draw the structures of the following : (i)HClO4 (ii) XeOF4 (b) (i) +3 oxidation state becomes more and more stable from As to Bi in the group. (ii) Sulphur in vapour state exhibits paramagnetism. (iii) Fluorine does not exhibit any positive oxidation state. (a) Account for the following : (i) Propanal is more reactive than propanone towards nucleophilic reagents. (ii) Electrophilic substitution in benzoic acid takes place at meta position. (iii)Carboxylic acids do not give characteristic reactions of carbonyl group. (a) Write the products formed when (CH3)3C-CHO reacts with the following reagents: (i) HCN (ii) Conc. NaOH OR 5 5 5 (a) Write structures of A, B, C and D in the following reaction sequence: PCl5 CH3COOH H2/Pd-BaSO4 A CH3 MgBr B C H3O+ LiAlH4 D (b) Arrange the following compounds in increasing order of their boiling points: CH3CHO, CH3CH2OH, CH3OCH3, CH3COOH

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