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CBSE Class 12 Pre Board 2019 : Chemistry - Prelim 2 (St Xavier's Sr. Sec. School, Delhi)

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Pre Board Examination 2019 Std. 12 21-01-2019 Set 2 Max. Marks : 70 Time : 3 hrs. CHEMISTRY General instructions: i) All questions are compulsory. ii) Section A : Q. No. 1 to 5 are short answer questions and carry 1 marks each. iii) Section B : Q. No. 6 to 12 are short answer questions and carry 2 marks each. iv) Section C : Q. No. 13 to 24 are short answer questions and carry 3 marks each. v) Section D : Q. No. 25 to 27 are long answer questions and carry 5 marks each. vi) There is no overall choice. However an internal choice has been provided in two questions of one mark, two questions of two marks, four questions of 3 marks and all the questions of five marks weightage. You have to attempt only one of the choices in such questions. vii) Use log tables if necessary, use of calculator not allowed. Section A 1. What type of magnetism is shown in the following alignment of magnetic moment? (OR) What type of point defect is produced when AgCl is doped with CdCl2? (1) 2. Write a method by which lyophobic colloids can be coagulated. (1) 3. On the basis of crystal field theory, write the electronic configuration of d in terms of t2g and eg in an octahedral field when o < P. (OR) Give evidence that [ Co (NH3)5Cl ]SO4 and [Co (NH3)5 SO4]Cl are ionisation isomers. (1) 4. Identify the compound which on hydrogenation produces an optically active compound from the following compounds: 5. What are reducing sugars? Give an example. 4 (1) (1) Section B 6. 3.9 g of benzoic acid dissolved in 49 g of benzene shows a depression in freezing point of 1.62 K. Calculate the van t Hoff factor and predict the nature of the solute (associated or dissociated) -1 -1 Molar mass of benzoic acid = 122 g mol , Kf for benzene = 4.9 K Kg Mol ) (OR) Calculate the molality of ethanol solution in which the mole fraction of water is 0.88. (2) 7. Identify the reaction and write the IUPAC name of the product formed. Br2 / Red Phosphorous a) CH3 CH2 COOH b) O Cl H2 Pd BaSO4 8. (OR) Write the structures and IUPAC names of cross aldol condensation products only of ethanal and propanal. (2) For a reaction R P, half life is observed to be independent of the initial concentration of reactants. What is the order of the reaction? Define activation energy of a reaction. (2) a) b) Std. 12 9. CHEMISTRY (Set 2) Give chemical reactions for the following: a) Kolbe s reaction b) Cannizzaro reaction Page 2 (2) 10. Write the mechanism of acid catalysed dehydration of ethanol to yield ethene. (2) 11. Name the two most important allotropes of sulphur. Which one of the two is stable at room temperature? (2) 12. Give reasons for the following: 2+ 2+ a) Mn is much more resistant than Fe towards oxidation. b) Transition metals and their many compounds act as catalysts. (2) Section C 13. Niobium crystallises in body centred cubic structure. If the atomic radius is 141.1 pm, calculate the density of niobium. (Atomic mass = 93u) 14. a) b) State Henry s law. Write one its application. What is the effect of temperature on the solubility of gases in liquids? Blood cells are isotonic with 0.9 % sodium chloride solution. What happens if we place blood cells in a solution containing i) 1.2 % sodium chloride solution. ii) 0.4 % sodium chloride solution. (3) (3) 15. An organic compound A with molecular formula C8H8O gives positive DNP and iodoform tests. It does not reduce Tollen s or Fehling s reagent and does not decolourise bromine water also. On oxidation with chromic acid, it gives carboxylic acid B with molecular formula C7H6O2. Deduce the structures of A and B (3) 16. Which one of the following compounds will undergo faster hydrolysis reaction by 1 SN mechanism? Justify your answer. CH2Cl (or) CH3 CH2 CH2 Cl (OR) A compound is formed by the substitution of two chlorine atoms for two hydrogen atoms in propane. Write the structures of isomers possible. Give the IUPAC name of the isomer which can show enantiomerism. 17. a) b) (3) Based on molecular forces what type of polymer is neoprene? Identify the monomers in the following polymer [ NH - (CH2)6 NH CO (CH2)4 CO - ]n c) What are copolymers? Give one example. 18. a) b) What are biodegradable and non-biodegradable detergents? Give one example each. Which class of drugs is used in sleeping pills? (3) 19. a) A colloidal sol is prepared by the given method in figure. What is the charge of AgI colloidal particles in the test tube? How is the sol formed, represented? b) Which of the following electrolytes is the most effective for the coagulation of Fe(OH)3 sol which is a positively charged sol? NaCl, Na2SO4 , Na3PO4 Define peptization. c) (3) (3) Std. 12 20. 21. What is the difference between fibrous proteins and globular proteins? How many peptide linkages are present in a tripeptide ? Write the name of the vitamin which is responsible for the coagulation of blood. (OR) Give three reactions of glucose which cannot be explained by its open chain structure. Write a) b) c) c) 23. Page 3 a) b) c) a) b) 22. CHEMISTRY (Set 2) the reactions involved in the following processes: Leaching of bauxite ore to prepare pure alumina. Refining of zirconium by van Arkel method. Recovery of gold after gold ore has been leached with NaCN. (OR) Write the principle of electrolytic refining. Why does copper obtained in the extraction from copper pyrites have a blistered appearance? What is the role of depressant in the froth floatation process? (3) (3) How do you prepare? i) KMnO4 from MnO2 ii) Na2Cr2O7 from Na2CrO4 (3) For a chemical reaction R P the variation in the concentration ln[R] vs time plot is given as y a) b) c) Predict the order of the reaction. In[R] What is the slope of the curve? What is the unit for rate constant for this reaction? x t(s) (OR) The rate constant of a first order decomposition of H2O2 is given by the following equation: 1.0 x 10 4 K T Calculate Ea for this reaction and rate constant k if its half life period be 200 minutes. -1 -1 R = 8.314 J K mol . (3) a) b) (3) log k 14.2 24. Define crystal field splitting energy. 2Write the hybridisation type and magnetic behaviour of the complex [Ni(CN)] . (Atomic No. Ni = 28) Section D 25. a) b) a) b) c) How would you account for the following: i) N2 is less reactive at room temperature. ii) Reducing character increases from HF to HI. iii) Chlorine water is a powerful bleaching agent. Draw the structures of the following molecules: i) Dibasic oxoacid of phosphorous. ii) Chloric acid (OR) Complete the following equations: i) Cu + H2SO4 ii) SO3 + H2O Arrange the following in the order of the property indicated against each set i) F2, I2, Cl2, Br2 (increasing order of bond dissociation enthalpy) ii) NH3, AsH3, SbH3, BiH3, PH3 (decreasing base strength) On adding NaOH to ammonium sulphate a colourless gas with pungent order is 2+ evolved which forms a blue coloured complex with Cu ion. Identify the gas. (5) Std. 12 26. a) b) c) CHEMISTRY (Set 2) Page 4 When a current of 0.75 A is passed through copper sulphate solution for 25 min, 0.369 g of copper is deposited at the cathode. Calculate the atomic mass of copper. Write the products of electrolysis of aqueous solution of NaCl with platinum electrodes. A voltaic cell is set up at 25o C with the following half cells: Al / Al3+ (0.001 M) and Ni / Ni2+ ( 0.50 M ) Write an equation for the reaction that occurs when the cell generates an electric current and determine the cell potential 1 1 (Eo Ni2+/ Ni = - 0.25 V, Eo Al3+ / Al = - 1.66 V, 1F = 96500C, R = 8.314 J K mol ) (OR) a) b) c) 27. a) How do metallic and ionic substances differ in conducting electricity? What type of battery is mercury cell? Why is it more advantageous than dry cell? Calculate e.m.f and G for the following cell at 298K. 2+ + Mg|Mg (0.01M) || Ag (0.0001M) | Ag 2+ + 1 1 (Eo Mg | Mg = 2.37V, Eo Ag |Ag = 0.80V, 1F = 96500C, R = 8.314 J K mol ) Complete the following reactions: O i) + NH2OH ii) COOH COOH b) c) a) b) c) + NH3 strong heating Give chemical tests to distinguish between the following pairs of compounds: i) Acetophenone and benzophenone ii) Aniline and benzylamine Carry out the following conversions: i) Ethanoic acid to propanoic acid ii) Nitrobenzene to benzoic acid (OR) Account for the following: i) Direct nitration of aniline yields significant amount of meta derivative. ii) Aniline does not undergo Friedel Crafts reaction. Arrange the following in the increasing order of basic strength in aqueous solution: NH3, CH3NH2, (CH3)2NH, (CH3)3N Write structures of A and B. NaOH + Br2 OH i) CH3 CH2 CN A B partial hydrolysis Sn + HCl (i) NaNO2 + HCl ii) C6H5NO2 A B (5) + (ii) H2O / H -x-x-x-x-x-x- (5)

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