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CBSE XII Pre Boards 2015 : CHEMISTRY with Answers (KV Chennai)

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KENDRIYA VIDYALAYA SANGATHAN CHENNAI REGION COMMON PRE-BOARD EXAMINATION 2014-15 CHEMISTRY CLASS-XII TIME:3HRS MAX.MARKS-70 Instructions: Answer all the questions. Questions 1 to 5are very short answer type and carry one mark each. Answer them in one word or in one sentence. Questions 6 to 10 are short answer type and carry 2 marks each. Answer them in 20 words. Questions 11 to 22 are short answer type and carry 3 marks each. Answer them in 30 words. Question 23 is value based question and carry 4 marks. Questions 24 to 26 are long answer type and carry 5 marks each. Answer them in 50 to 60 words. All 5 mark questions, one 3 mark question and one 2 mark question have internal choice. There is no overall choice. Use log book wherever needed. Use of calculator or any other electronic item is strictly prohibited. 1. 2. 3. 4. Write the IUPAC name of p-Cl C6H5CHO. (1) What are Nucleosides? (1) Ethers are highly volatile than alcohols. Give reason. (1) Why are the diazonium salt formed by aliphatic amines unstable whereas that of aromatic amines stable. (1) 5. What is the basic principle involved in zone refining method of purification of metals. (1) 6. In the Button cell, widely used in watches, the following reaction takes place: Zn(s) +Ag2O(s) + H2O Z +2(aq) + 2Ag(s)+ 2OH-(aq) CalculateE0cell and standard Gibbs energy for the reaction. (Given: E0Ag+ / Ag = + 0.80 V ; E0Zn+ / Zn = - 0.76 V )(2) OR What is meant by over voltage and electro chemical equivalent in electro chemistry? 7. Haloarenes are less reactive than haloalkanes towards nucleophilic substitution reactions. Give two reasons. (2) 8. Distinguish between(2) a. Pentan-3-one and Pentan-2-one. b. Ethanal and propanol. 9. What type of deviation from ideal behavior does chloroform and acetone mixture show? Explain. (2) 10. Write one example each for Finkelstine reaction and Wurtz reaction. (2) 11. Explain the following with examplec. Food preservatives. (3) a. Cationic detergents b. Broad spectrum antibiotics 12. What is hydrometallurgy? W A W CaCO3 added in blast furnace of extraction of iron? (1+2) 13. Draw the structure of- a. XeOF4 b. Pyrophosporic acid c. Sulphuric acid. (3) 14. An organic compound (A) (molecular formulaC8H16O2) was hydrolyzed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid produced (B). (C) on dehydration gives but-1-ene. Write equations for the reactions involved. (3) OR An organic compound C9H10O forms 2,4-DNP T undergoes Cannizzaro reaction. On vigorous oxidation, it gives 1,2-benzenedicarboxylic acid. Identify the compound. 15. 1. Write the structure of monomers used for the preparation of Buna N. (1+1+1) 2. What is vulcanization of rubber? 3. Give one example each for elastomer and fibrous polymer. 16. What is molar conductivity of an electrolyte? Calculate the equilibrium constant of the reaction Cu(s) + 2Ag+(aq) Cu2+(aq) + 2Ag(s). Given that the E Ag+/Ag = 0.8v and E Cu2+/Cu= 0.34v. (1+2) 17. Differentiate between Lyophilic and lyophobic colloids. What is the significance of Brownian movement in colloids? (1+2) 218. a. Explain on the basis of valence bond theorythat [Ni(CN)4] ion with square planar structure is diamagnetic and the [NiCl4]2- ion with tetrahedral geometry is paramagnetic. b.Drawadiagram to show the orbital in tetrahedral field.(3) 19. a. How do you prove that glucose contains a 1 alcohol group? b. What is a tripeptide? c. Name the vitamin whose deficiency cause pernicious anemia.(1+1+1) 20. Define osmotic pressure of a solution. 18g of C6H12O6 is dissolved in 1kg of water in a saucepan. At what temperature will water boil at 1.013bar? K b for water is 0.52Kkgmol-1 (3) 21. a. How will you convert propan 1 ol topropan 2 ol? b. How will you distinguish between 1 phenyl ethanol to 2 phenyl ethanol? 22. Give reason (3) a. Aniline does not undergo Friedal Crafts reaction. b. Gabriel pthalimide synthesis is not a suitable method to prepare aromatic primary amine. c. Aniline is less basic than ethanamine. 23. Raman and John are fruit sellers. Raman always arranges the fruits in an orderly fashion. John keeps the fruits as a heap. As a student of science, does this make any difference to you? What value does this add to your life? By seeing such orderly arrangement of fruits in shops what differences are you reminded of quartz and quartz glass? Does it have any impact in understanding why diamond is used as gemstone? (4) 24. A ements:(5) a. They posses high enthalpy of atomization. b. They and their compounds act as catalyst. c. They easily form alloys d. They form complex compound. e. They show magnetic character. OR a. Write one similarity and two differences between Lanthanides and actinides. (3) b. Write equation for the reaction between KMnO4 and KI in acid and alkaline medium.(2) 25. a. Arrange the following in the increasing order of properties mentioned.(3) i. H2Te, H2Se,H2O,H2S (Boiling point) ii. PH3, NH3, SbH3, AsH3, BiH3 (Basic strength) iii. HBr, HCl, HI, HF ( Acidic character) c. Write the equations involved in the preparation of H2SO4 by contact process. (2) OR a. Explain why? (3) i. S2 is paramagnetic in nature. ii. O3 acts as a powerful oxidizing agent. iii. 'He is used in diving apparatus. b. How is PH3 purified? Write equation. (2) 26. a. What is order of a reaction? How does it differ from molecularity of the reaction? (2) b. Calculate the rate constant of the reaction at 700K if the energy of activation for the following reaction is 209kJ/mol and the rate constant at 600K is 1.60x10-5S-1. C2H5I (g) C2H4(g) + HI(g) (3) OR a. What is pseudo first order reaction? Write one example. (2) b. The following data were obtained during the first order thermal decomposition of N2O5(g) at constant volume.2N2O5(g) 2N2O4(g)+O2(g) (3) Sl.No. Time/s Total Pressure/(atm) 1. 0 0.5 2. 100 0.512 Calculate the rate constant. *************************** KENDRIYA VIDYALAYA SANGATHAN CHENNAI REGION COMMON PRE-BOARD EXAMINATION 2014-15 CLASS XII- CHEMISTRY Scoring Key 1. 2. 3. 4. 5. 6. 4-chlorobenzaldehyde. They are combination of pentose sugar and nitrogenous base. Because ethers cannot form intermolecular hydrogen bonding among themselves. Due to resonance stabilization. (1) The impurities are more soluble in the melt than in the solid metal. E0cell = E0cathod -E0anode = + 0.80 + 0.76= + 1.56 V ; (1) rG 7. 8. 9. 10. (1) (1) (1) 0 = -nFE0cell = - 2 x 96500 x 1.56 = -301080 j mol-1 = -301.08 kj mol-1 (1) (OR) Over voltage: Extra potential, which is required to be applied across the electrodes when an electrode reaction is kinetically slow (Any other suitable answer) (1) The mass of metal deposited at the cathode when one coloumb of charge is passed through an electrolyte. (1) 1. The C-X bond in haloarenes have double bond character due to resonance. (2) 2 2. The halogen atom is attached to a more electro negative Sp hybridized carbon, in haloarenes. a. Pentan-3-one does not give yellow ppt when treated with I2/NaOH (Iodoform reaction), whereas pentan-2-one gives yellow ppt. (1) E A Propanol doesnot. ( any other suitable test) (1) Negative deviation. Since acetone, when treated with chloroform, forms hydrogen bonding. So H = - ve and V = - ve. (2) Finkelstein Reaction Swarts Reaction 11. a. The detergents in which the cation acts as cleansing agent by forming micelle. Ex. Cetyltrimethyl ammonium bromide. (1/2+1/2) b. The antibiotic which is useful in treating gram positive and gram negative bacteria. Ex. Chloramphenicol. (1/2+1/2) c. Chemicals which are added to food materials to prevent them from spoiling. Ex.Sodium benzoate. (1/2+1/2) (Suitable answers can be given marks) 12. Extraction of metal from its ore by adding suitable reagent which will convert the metal in to a soluble compound and then separating the metal from the solution. (1) To reduce the melting point of alumina. (1) (1) It acts as flux to remove SiO2 as slag. 13. (1+1+1) a) Square pyramidal b) Pyrophosphoric Acid c) Sulphuric acid 14. C8H16O2 H+ CH3-CH2-CH2-COOH + CH3-CH2-CH2-CH2-OH (B) (C) (1) CH3-CH2-CH2-CH2-OH CrO3/H2SO4 (C) CH3-CH2-CH2-CH2-OH Con.H2SO4 CH3-CH2-CH2-COOH (1) (B) CH2=CH-CH2-CH3 (1) OR As the organic compound gives 2,4-DNP derivative it should be a carbonyl compound. A As it undergoes cannizzaro reaction, it should be an aldehyde without - hydrogen. As on vigorous oxidation it gives 1,2-benzenedicarboxylic acid it must be an aromatic aldehyde - ethylbenzaldehyde. S (1+1+1) Equations also can be given marks. 15. 1. CH2=CH-CH=CH2 & CH2=CH-CN (for name alone no marks) (1/2+1/2) 2. Hardening of rubber by strongly heating it with suitable amount of sulphur. (1) 3. Elastomers Rubber Fibers Terylene. (1/2+1/2) 16. The conductivity of a particular volume of a solution which contain one mole of an electrolyte(1) (1/2) E cell = 0.8-0.34=0.46v (1 ) 17. Any two difference (2) Lyophillic-solvent attractive colloids ,Cannot be easily coagulated, reversible sols. Lyophobic- solvent repelling colloids, readily precipitated on adding any electrolyte , irreversible. Brownian movement accounts for the stability of the colloids. (1) 2+ 18. a. Writing the electronic configuration of Ni ion. (1) CN- ligand is a strong field ligand. So pairing of electron takes place and diamagnetic in nature. (1/2) ClS b. (1) 19. a. When treated with Nitric acid it gives saccharic acid. (1) b. A tripeptide is made up of 3 amino acid molecules joined by peptide linkage. c. Vitamin B12. 20. Pressure that just stops the flow of solvent or any correct definition (2) P,Br2 Alc.KOH (1) (1) (1) H+,H2O 21. a. CH3CH2CH2OH CH 3CH2CH2Br CH3CH=CH2 CH3CHOH CH3 b. 1-Phenyl Ethanol, having terminal methyl groupanswersforiodoform test. 22. a. since aniline reacts with AlCl3 which is a lewis acid. (1) b. Chlorobenzene does not react with potassium phthalimide due to C-X double bond character. (1) T N 23. Any suitable answer likeYes, the orderly arrangement of anything helps the effective usage of space (1) Aesthetic sense. (1) Quartz is a Crystalline solid and quartz glass is a amorphous solid. (1) Due to orderly arrangement diamond has high refractive index and so it is used as gem stone.(1) 24. T S -1)d orbitals. (1) b. They show variable oxidation state and they can change their oxidation state from one to other during reaction. (1) c. Due to their almost similar size they can substitute one another in their crystal lattice. (1) T T y can be paramagnetic, OR a. Similarity: Both form more compounds in +3 states. Difference: Actinides show more number of variable oxidation state than Lanthanoids. Actinoid contraction is more pronounced than lanthanoid contraction. (1+2) + 2+ 2Mn + 8H2O + 5I2. (1+1) b. 10I + 2MnO4 + 16H 2MnO2 + 2OH + IO3 . 2MnO4 + H2O + I 25. a. i. H2S,H2Se,H2Te,H2O. ii. BiH3,SbH3,AsH3,PH3,NH3. iii. HF,HCl,HBr,HI (1+1+1) b.(2) H2S2O7+H2O H2SO4 OR a. i. S2 is similar to O2 and has unpaired electron in its * antibonding orbital. ii. It decomposes to give nascent oxygen. (or Equation) (1) (1) iii. It reduces the activity of oxygen/ It does not dissolve in blood like Nitrogen. (1) PH 4I + KOH PH 3 + KI + H2O (1+1) b. PH3 +HI 26. a. The sum of the power of the concentration terms in the rate law of a reaction. Any one difference like order is the experimental valueandmolecularityis the number of molecules taking part in the chemical reaction. (1+1) b. (1+1+1) OR a. The reaction in which two reactants are involved but the rate of the reaction depends on only one reactant due to the large excess of the other. (1) Any one Ex (1) b. (3) X=Pt-0.5 **********************

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