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CBSE Class 12 Board Exam 2020 : Chemistry (Series 4)

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Series : HMJ/4 OSS/1GRLH/1 SET 1 . Code No. . 56/4/1 - - Roll No. Candidates must write the Code on the title page of the answer-book. (I) - (I) 15 (II) - (II) - - NOTE Please check that this question paper contains 15 printed pages. Code number given on the right hand side of the question paper should be written on the title page of the answer-book by the candidate. (III) Please check that this question paper contains 37 questions. (III) - 37 (IV) (IV) Please write down the Serial Number of the question in the , (V) - 15 (V) - 10.15 10.15 10.30 - - answer-book before attempting it. 15 minute time has been allotted to read this question paper. The question paper will be distributed at 10.15 a.m. From 10.15 a.m. to 10.30 a.m., the students will read the question paper only and will not write any answer on the answer-book during this period. ( ) CHEMISTRY (Theory) {ZYm [aV g : 3 K Q>o A{YH$V A H$ : 70 Maximum Marks : 70 Time allowed : 3 hours .56/4/1. 321A 1 P.T.O. - , , (ii) - - 1 20 - , 1 (iii) - - 21 27 - , 2 (iv) - - 28 34 - -1 , 3 (v) - - 35 37 - -2 , 5 (vi) , - , - - (vii) , , (viii) (i) 1 5 AgNO3 KI - , , , , 1. ? 2. ? 3. AgNO3 KI - ? 4. 5. KI K2SO4 - - ? .56/4/1. 2 General Instructions : Read the following instructions very carefully and strictly follow them : (i) Question paper comprises four sections A, B, C and D. (ii) There are 37 questions in the question paper. All questions are compulsory. (iii) Section A : Q. No. 1 to 20 are very short answer type questions carrying one mark each. Answer these questions in one word or one sentence. (iv) Section B : Q. No. 21 to 27 are short answer type questions carrying two marks each. (v) Section C : Q. No. 28 to 34 are long answer type-I questions carrying three marks each. (vi) Section D : Q. No. 35 to 37 are long answer type-II questions carrying five marks each. (vii) There is NO overall choice in the question paper. However, an internal choice has been provided in 2 questions of two marks, 2 questions of three marks and all the 3 questions of five marks. You have to attempt only one of the choices in such questions. (viii) However, separate instructions are given with each section and question, wherever necessary. (ix) Use of calculators and log tables is NOT permitted. SECTION A Read the given passage and answer the questions 1 to 5 that follow : Colloidal particles always carry an electric charge which may be either positive or negative. For example, when AgNO3 solution is added to KI solution, a negatively charged colloidal sol is obtained. The presence of equal and similar charges on colloidal particles provide stability to the colloidal sol and if, somehow, charge is removed, coagulation of sol occurs. Lyophobic sols are readily coagulated as compare to lyophilic sols. 1. What is the reason for the charge on sol particles ? 2. Why the presence of equal and similar charges on colloidal particles provide stability ? 3. Why a negatively charged sol is obtained on adding AgNO3 solution to KI solution ? 4. Name one method by which coagulation of lyophobic sol can be carried out. 5. Out of KI or K2SO4, which electrolyte is better in the coagulation of positive sol ? .56/4/1. 3 P.T.O. 6 10 : 6. 7. 8. SN1 ? C3H9N NaOH 9. - ? , , 10. 11 15 : 11. [Co(NH3)5Cl] Cl2 ? (a) 12. 4 (b) 2 (c) 3 (d) 5 (d) k 2.303 (a) PbO2, PbSO4 (b) Pb PbSO4 (c) H2SO4 (d) 13. ln[R] k (a) + k (b) 2.303 ( [R] ) (c) k 14. [Co(NH3)4 Cl2] Br2 [Co(NH3)4 Br2] Cl2 (a) (c) (b) (d) 15. - (a) (c) .56/4/1. (d) (b) 4 Questions 6 to 10 are one word answers : 6. Name the method applied for the concentration of Bauxite ore in the extraction of Aluminium. 7. Out of SN1 reaction ? and , which one is more reactive towards 8. Write an isomer of C3H9N which gives foul smell of isocyanide when treated with chloroform and ethanolic NaOH. 9. Which one of the following is an antidepressant drug ? Chloramphenicol, Luminal, Bithional 10. Write the name of component of starch which is water soluble. Questions 11 to 15 are Multiple Choice Questions : 11. How many ions are produced from the complex [Co(NH 3)5Cl] Cl2 in solution ? (a) 4 (b) 2 (c) 3 (d) 5 12. In a lead storage battery (a) PbO2 is reduced to PbSO4 at the cathode. (b) Pb is oxidised to PbSO4 at the anode. (c) Both electrodes are immersed in the same aqueous solution of H2SO4. (d) All the above are true. 13. The slope in the plot of ln [R] Vs. time gives k (a) + k (b) (c) k 2.303 (where [R] is the final concentration of reactant.) (d) k 2.303 14. The pair [Co(NH3)4 Cl2] Br2 and [Co(NH3)4 Br2] Cl2 will show (a) (c) Linkage isomerism Ionization isomerism (b) (d) Hydrate isomerism Coordinate isomerism 15. An -helix is a structural feature of (a) Sucrose (c) Nucleotides (b) (d) Polypeptides Starch .56/4/1. 5 P.T.O. 16 20 : (A) (A) (R) (R), (A) (B) (A) (R) , (R), (A) (C) (A) , (R) (D) (A) , (R) 16. (A) : F2 (R) : 17. (A) : (CH3)3 C O CH3 HI (CH3)3 C I CH3OH (R) : SN1 18. (A) : (R) : (n 1)d ns 19. (A) : (R) : 20. (A) : - (R) : 20 1 = 20 21. (i) ? (ii) ? 1+1=2 22. (a) (b) ( ) (i) Cu2S Cu (ii) [Ag (CN)2] Ag .56/4/1. 6 1+1=2 1+1=2 Questions 16 to 20 : (A) Both Assertion (A) and Reason (R) are correct statements, and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are correct statements, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is correct, but Reason (R) is wrong statement. (D) Assertion (A) is wrong, but Reason (R) is correct statement. 16. Assertion (A) : F2 is a strong oxidising agent. Reason (R) : Electron gain enthalpy of fluorine is less negative. 17. Assertion (A) : (CH3)3 C O CH3 gives (CH3)3 C I and CH3OH on Reason (R) treatment with HI. : The reaction occurs by SN1 mechanism. 18. Assertion (A) : Transition metals have low melting points. Reason (R) : The involvement of greater number of (n 1)d and ns electrons in the interatomic metallic bonding. 19. Assertion (A) : Hydrolysis of an ester follows first order kinetics. Reason (R) : Concentration of water remains nearly constant during the course of the reaction. 20. Assertion (A) : Benzoic acid does not undergo Friedal-Crafts reaction. Reason (R) : The carboxyl group is activating and undergo electrophilic substitution reaction. 20 1 = 20 SECTION B 21. What happens when (i) a pressure greater than osmotic pressure is applied on the solution side separated from solvent by a semipermeable membrane ? (ii) acetone is added to pure ethanol ? 1+1=2 22. Write the principle of the following refining methods : (a) (b) vapour phase refining chromatography OR Write chemical equations involved to obtain : (i) Cu from Cu2S (ii) .56/4/1. Ag from [Ag (CN)2] complex 1+1=2 1+1=2 7 P.T.O. 23. (MnO2) KMnO4 2 (i) 2 (II) (ii) (II) (Cr2O 7 ) 24. 1+1=2 (i) [Ni(CN)4]2 (ii) [Fe(H2O)6]2+ ( : Ni = 28, Fe = 26) 25. (i) 26. ( ) (ii) 1+1=2 (i) 27. 1+1=2 (ii) 1+1=2 298 K 760 mm Hg CO2 (298 K CO2 KH = 1.25 106 mm Hg ) 2 (M = 122 g mol 1) 35g 2.94 K ? 28. 5g ( Kf = 4.9 K kg mol 1) 3 29. N2O5 k = (2.5 1014 s 1) e( 25000K)/T Ea 300 30. 3 (i) .56/4/1. -6 (ii) (PVC) 8 (iii) 1+1+1=3 23. Write the balanced chemical equations involved in the preparation of KMnO4 from pyrolusite ore (MnO2). 2 OR Write the balanced ionic equations showing the oxidising action of 2 acidified dichromate (Cr2O 7 ) solution with (i) Iron (II) Ion and (ii) tin (II) ion. 1+1=2 24. Write the IUPAC names and hybridisation of the following complexes : (i) [Ni(CN)4]2 (ii) [Fe(H2O)6]2+ (Given : Atomic number Ni = 28, Fe = 26) 25. Define the following terms with a suitable example in each : (i) Antibiotics (ii) Antiseptics 1+1=2 1+1=2 26. Write the reactions showing the presence of following in the open structure of glucose : (i) a carbonyl group (ii) Straight chain with six carbon atoms 1+1=2 27. State Henry s law. Calculate the solubility of CO2 in water at 298 K under 760 mm Hg. (KH for CO2 in water at 298 K is 1.25 106 mm Hg) 2 SECTION C 28. The freezing point of a solution containing 5g of benzoic acid (M = 122 g mol 1) in 35g of benzene is depressed by 2.94 K. What is the percentage association of benzoic acid if it forms a dimer in solution ? (Kf for benzene = 4.9 K kg mol 1) 3 29. The rate constant for the first order decomposition of N 2O5 is given by the following equation : k = (2.5 1014 s 1) e( 25000K)/T Calculate Ea for this reaction and rate constant if its half-life period be 300 minutes. 3 30. Write the name and structures of monomer(s) in the following polymers : (i) Nylon-6 (ii) PVC (iii) Neoprene 1 + 1 + 1 = 3 .56/4/1. 9 P.T.O. 31. Cr2+, Cu2+, Cu+, Fe2+, Fe3+, Mn3+ (i) (ii) (iii) 1+1+1=3 32. (i) 2, 2, 3- -3- - (ii) - ? (iii) (A) (B) Na/ (A) Mg/ (B) 1+1+1=3 ? (i) -1- 1- (ii) (iii) 33. (i) : 1+1+1=3 (CH3)2NH, CH3NH2, C6H5NH2 (ii) : (CH3)3N, (CH3)2NH, CH3NH2 (iii) : (C2H5)2NH, (C2H5)3N, C2H5NH2 34. 1+1+1=3 / : (i) (iii) PCC (CH3CO)2O CH3COOH (ii) H3O+ + CH3MgBr 1+1+1=3 .56/4/1. 10 31. Following ions are given : Cr2+, Cu2+, Cu+, Fe2+, Fe3+, Mn3+ Identify the ion which is (i) a strong reducing agent. (ii) unstable in aqueous solution. (iii) a strong oxiding agent. Give suitable reason in each. 32. (i) (ii) 1+1+1=3 Write the structure of major alkene formed by -elimination of 2, 2, 3 trimethyl 3 bromopentane with sodium ethoxide in ethanol. Which one of the compounds in the following pairs is chiral ? (iii) Identify (A) and (B) in the following : Na/dry ether (A) Mg/dry ether (B) 1+1+1=3 OR How can you convert the following ? (i) But-1-ene to 1-iodobutane (ii) Benzene to acetophenone (iii) Ethanol to propanenitrile 1+1+1=3 33. Arrange the following compounds as directed : (i) In increasing order of solubility in water : (CH3)2NH, CH3NH2, C6H5NH2 (ii) In decreasing order of basic strength in aqueous solution : (CH3)3N, (CH3)2NH, CH3NH2 (iii) In increasing order of boiling point : (C2H5)2NH, (C2H5)3N, C2H5NH2 1+1+1=3 34. Write the product(s) of the following reactions : (i) PCC (iii) H3O+ + CH3MgBr (ii) (CH3CO)2O CH3COOH 1+1+1=3 OR .56/4/1. 11 P.T.O. (a) SN1 NaOH (CH ) C Br (CH ) C OH + NaBr 3 3 (b) 3 3 2- -2- 2 + 1 = 3 35. (a) 0.05 M KOH 5 103 ohm 0.625 cm2 50 cm , (b) CuCl2 o o ( : E 2 = + 0.34 V, E 1 Cu /Cu Cl /Cl = + 1.36 V 2 2 o E = H /H 2 (g), Pt o 0.00 V, E 1 2 O 2 /H 2O = + 1.23 V ) 3+2=5 (a) e.m.f. : Zn(s)/Zn2+ (0.1 M) || (0.01 M) Ag+/Ag(s) : E oZn 2 /Zn = 0.76 V, E oAg /Ag = + 0.80 V [ : log 10 = 1] (b) X Y X 2.5 Y 25 ?3 + 2 = 5 (A) C4H8O , 2, 4- . . . - NaOH I2 (A) NaBH4 (B) H2SO4 (C) (C) (A), (B) (C) (A) (i) NaOH/I2 (ii) NaBH4 (b) : (i) (ii) - 3+2=5 36. (a) .56/4/1. 12 (a) Write the mechanism of the following S N1 reaction : Aq. NaOH (CH3) C Br (CH3) C OH + NaBr (b) 35. (a) (b) 3 3 Write the equation for the preparation methoxypropane by Williamson synthesis. of 2-methyl-22+1=3 SECTION D The electrical resistance of a column of 0.05 M KOH solution of length 50 cm and area of cross-section 0.625 cm2 is 5 103 ohm. Calculate its resistivity, conductivity and molar conductivity. Predict the products of electrolysis of an aqueous solution of CuCl2 with platinum electrodes. (Given : E E (a) 36. (a) = + 0.34 V, E o H /H 2 (g), Pt o 12 Cl2/Cl = + 1.36 V o = 0.00 V, E 1 2 O 2 /H 2O = + 1.23 V ) 3+2=5 OR Calculate e.m.f. of the following cell : Zn(s)/Zn2+ (0.1 M) || (0.01 M) Ag+/Ag(s) Given : E (b) o Cu 2 /Cu o Zn 2 /Zn = 0.76 V, E o Ag /Ag = + 0.80 V [Given : log 10 = 1] X and Y are two electrolytes. On dilution molar conductivity of X increases 2.5 times while that Y increases 25 times. Which of the two is a weak electrolyte and why ? 3+2=5 An organic compound (A) having molecular formula C4H8O gives orange red precipitate with 2, 4-DNP reagent. It does not reduce Tollens reagent but gives yellow precipitate of iodoform on heating with NaOH and I2. Compound (A) on reduction with NaBH4 gives compound (B) which undergoes dehydration reaction on heating with conc. H2SO4 to form compound (C). Compound (C) on Ozonolysis gives two molecules of ethanal. Identify (A), (B) and (C) and write their structures. Write the reactions of compound (A) with (i) NaOH/I2 and (ii) NaBH4. (b) .56/4/1. Give reasons : (i) Oxidation of propanal is easier than propanone. (ii) -hydrogen of aldehydes and ketones is acidic in nature. OR 13 3+2=5 P.T.O. : (i) (ii) (b) / (a) (i) (ii) (c) (i) DIBAL H CH3 CH=CH CH2 CN (ii) H3O+ CrO3 CH3 CH2 OH ? 2+2+1=5 : (i) 2 (ii) HF HI (iii) SO2 (b) S O S (c) : 37. (a) XeF2 + H2O 3+1+1=5 (a) 16 (i) (ii) (iii) (b) : S + H2SO4 ( ) Cl2 + NaOH ( ) 3+1+1=5 ___________ .56/4/1. 14 (a) (b) (c) 37. (a) (b) (c) (a) (b) Draw structures of the following derivatives : (i) Cyanohydrin of cyclobutanone (ii) Hemiacetal of ethanal Write the major product(s) in the following : (i) (i) DIBAL H CH3 CH=CH CH2 CN (ii) H3O+ (ii) CrO3 CH3 CH2 OH How can you distinguish between propanal and propanone ? 2 + 2 + 1 = 5 Account for the following : (i) Tendency to show 2 oxidation state decreases from oxygen to tellurium. (ii) Acidic character increases from HF to HI. (iii) Moist SO2 gas acts as a reducing agent. Draw the structure of an oxoacid of sulphur containing S O S linkage. Complete the following equation : XeF2 + H2O 3+1+1=5 OR Among the hydrides of group 16, write the hydride (i) Which is a strong reducing agent. (ii) Which has maximum bond angle. (iii) Which is most thermally stable. Give suitable reason in each. Complete the following equations : S + H2SO4 (Conc.) Cl2 + NaOH (Cold and dilute) 3+1+1=5 ___________ .56/4/1. 15 P.T.O. .56/4/1. 16

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