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CBSE Pre Board Class 12 2020 : Chemistry (The Indian Public School, Dehradun)

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Kishor Bisht
The Indian Public School, Dehradun

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The Indian Public School, Dehradun First Pre-Board Examination- 2019-20 Chemistry / Class XII-Science/ /04.12.2019 SET-A MM: 70 Time: 3:15 Hr General Instructions: KSB - 25 (a) All questions are compulsory. (b) Section A: Q.no. 1 to 20 are very short answer questions (objective type) and carry 1 mark each. (c) Section B: Q.no. 21 to 27 are short answer questions and carry 2 marks each. (d) Section C: Q.no. 28 to 34 are long answer questions and carry 3 marks each. (e) Section D: Q.no. 35 to 37 are also long answer questions and carry 5 marks each. (f) There is no overall choice. However, an internal choice has been provided in two questions of two marks, two questions of three marks and all the three questions of five marks weightage. You must attempt only one of the choices in such questions. (g) Use log tables if necessary, use of calculators is not allowed SECTION - A Read the given passage and answer the questions 1 to 3 that follow: A graph between x/m and the pressure P of the gas at constant temperature is called adsorption isotherm. Where x is the number of mole of the adsorbate and m is the mass of the adsorbent, Adsorption isotherm of different shapes have been experimentally observed. According to the Frundlich adsorption isotherm. x/m= kp1/n where k and n are constant parameter depending open the nature of the solid and the gas. Q1. In the given isotherm select the incorrect statement: (a) x/m p1/n along OA (b) x/m p0 When point B is reached (c) x/m does not increase as rapidly with pressure along BC due to less surface area available for adsorption. (d) Nature of isotherm is different for two gases for same adsorbent Q2. Adsorption isotherm for log(x/m) and log p was found of the type This is true when: (a) P=0 (b) p=1 (c) 1/n=1 (d) p<1 Q3. Graph between log(x/m) and log p is straight line at angle 450 with intercept OA as shown. Hence, (x/m) at a pressure of 2 atm is: (a) 2 (b) 4 (c) 8 (d) 1 Questions 4 and 5 are match the following: Q4. (A) (B) (C) (D) Column-I Conductance Conductivity Molar Conductivity Resistivity Column-II (P) Sm-1 (Q) S-1m (R) Sm2mol-1 (S) S (A) (B) (C) (D) Column-I Raoult s Law Henry s Law Osmatic pressure Elevation in boiling point Column-II (P) = CRT (Q) p= x1p10+ x2p20 (R) Tb =Kbm (S) p= KHx Q5. Questions 6 to 10 are one word answers: Q6. Adsorption is an exothermic reaction. Why? Q7. On the basis of crystal field theory, Write the electronic configuration of d6 in term of t2g and eg in an octahedral field when o < P. Q8. A solution of KOH hydrolyses CH3CHClCH2CH3 and CH3CH2CH2CH2Cl. Which one of these is more easily hydrolyzed and Why ? Q9. Write the names and draw the structure of monomers of Nylone-6 polymer. Q10. The electronic configuration of a transition element in +3 oxidation state is [Ar],3d7. Find out its atomic number. Questions 11 to 15 are multiple choice questions: Q11. The incorrect statement about LDP is: (a) It is obtained through the free radical addition of ethene. (b) It consists of linear molecules. (c) It is obtained by the H-atom abstraction. (d) Peroxide is used as an initiator. Q12. Which of the following species is Diamagnetic ? (a) [NiCl4]2(b) K3[Fe(CN)6] (c) [Ni(CO)4] (d) [Co(CN)6]3Q13. Which of the following expression is correct for zero order and first order respectively [ where a is the initial concentration]? (a) t1/2 a; t1/2 1/a (b) t1/2 a ; t1/2 a0 (b) t1/2 a0 ; t1/2 a (d) t1/2 a ; t1/2 1/a2 Q14. Which of the following reaction is used for the conversion of ketone into hydrocarbons? (a) Aldol condensation (b) Wolf-Kishner Reaction (c) Reimer- Tiemann Reaction (d) Rosenmunds Reaction Q15. A solution of acetone in ethanol (a) Obeys Raoult s law (b) Show a Negative deviation from Raoult s law (c) Show a Positive deviation from Raoult s law (d) Behaves like a near ideal solution. Questions 16 to 20 : (A)Both assertion and reason are correct statements, and reason is the correct explanation of the assertion. (B) Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion. (C) Assertion is correct, but reason is wrong statement. (D)Assertion is wrong, but reason is correct statement. Q16. Assertion: Acetic acid does not give haloform reaction. Reason: Acetic acid has no hydrogen. Q17. Assertion: Carbylamines reaction involves chemical reaction between 10 amine and chloroform in basic medium. Reason: In Carbylamines reaction, -NH2 group change into -NC group. Q18. Assertion: Disruption of the natural structure of a protein is called denaturation. Reason: The change in colour and appearance of egg during cooking is due to denaturation. Q19. Assertion: Bakelite is co- polymer. Reason: Bakelite is thermosetting material. Q20. Assertion: The Acidity of alcohols follows the order 10>20>30. Reason: The +I effect of alkyl group (30 >20 > 30) Favors the dissociation of -o-H group. SECTION : B Q21. Q22. Q23. Q24. Q25. Q26. Q27. Calculate the number of lone pairs on central atom in the following molecule and predict the geometry. BrF 5 Draw one of the geometrical isomers of the complex [Pt(en)2 Cl2 ]2+ which is optically inactive. Also write the name of this entity according to the IUPAC nomenclature. OR Discuss the bonding in the coordination entity [CO(NH3)6 ]3+ on the basis of valence bond theory. Also, comment on the geometry and spin of the given entity. (Atomic no. of Co= 27) Calculate the emf of the following cell at 298 K : Cr(s) / Cr3+ (0.1M) // Fe2+ (0.01M) / Fe(s) [Given : E0 Cell = + 0.30 V] OR The conductivity of 10-3 mol /L acetic acid at 250 C is 4.1 x 10 -5 S cm-1 . Calculate its degree of dissociation, if 0 m for acetic acid at 250 C is 390.5 S cm2 mol-1 . Draw the structures of any two isomeric alcohols (other than 1o alcohols) having molecular formula C5H12O and give their IUPAC names. Name the following: (a) A transition metal which does not exhibit variation in oxidation state in its compounds. (b) A compound where the transition metal is in the +7 oxidation state. (c) A member of the lanthanoid series which is well known to exhibit +4 oxidation state. (d) Ore used in the preparation of Potassium dichromate. Define the following term in relation to proteins: (i) Peptide bond (ii) A glycoside linkage Phenol associated in benzene to a certain extent to form a dimer. A solution containing 20g of phenol in 1Kg of benzene has its freezing point lowered by 0.69K. Calculate the fraction of phenol that has dimerized ( Given Kf= 5.1KKgmol-1) SECTION : C Q28. Q29. What are the following substances? Give one example of each one of them. (i) Tranquilizers (ii) Food preservatives (iii) Synthetic detergents Describe how the following steps can be carried out? (a) Recovery of Gold from leached gold metal complex. (b) Conversion of Zirconium iodide to pure Zirconium. (c) Formation of slag in the extraction of copper. (Write the chemical equations also for the reactions involved) 3 OR Q30. Q31. Q32. Q33. Explain the use of the following: a) NaCN in Froth Floatation Method. b) Carbon monoxide in Mond process. c) Coke in the extraction of Zinc from Zinc Oxide. Give the IUPAC name of the product formed when: (i) 2-Methyl-1-bromopropane is treated with sodium in the presence of dry ether. (ii) 1- Methyl cyclohexene is treated with HI. (iii) Chloroethane is treated with silver nitrite. (i) 0.1 M KCl solution offered a resistance of 100 ohms in a conductivity cell at 298 K. If the cell constant of the cell is 1.29 cm-1 , calculate the molar conductivity of KCl solution. (ii) Define the second law of Faraday s for electrolysis. (a)Differentiate between thermoplastic and thermosetting polymers. Give one example of each. (b) Write the structures of the monomers used for getting the following polymers: (i) Nylon-6, 6 (ii) Melamine-formaldehyde polymer (iii) Buna-S (iv) PHBV Give reasons : (i) pKa of O2N CH2 COOH is lower than that of CH3 COOH. (ii) Give simple chemical tests to distinguish between the following pairs of compounds. (a) Ethanal and Propanal (b) Pentan-2-one and Pentan-3-one OR Write the Name reaction for the following (a) HVZ Reaction (b) Wolff Kishner Reaction Q34. (iii) Aldol Condensation Reaction 3.9 g of benzoic acid dissolved in 49 g of benzene shows a depression in freezing points of 1.62 K. Calculate the van t Hoff factor and predict the nature of solute (associated or dissociated). (Given: Molar mass of benzoic acid = , for benzene = 4.9 K Kg ) SECTION : D Q35. (a) Write the rate law for a first order reaction. Justify the statement that half life for a first order reaction is independent of the initial concentration of the reactant. (b) For a first order reaction, show that the time required for 99% completion of a first order reaction is twice the time required for the completion of 90%. OR (a) List the factors on which the rate of a chemical reaction depends. (b) The following data were obtained during the first order thermal decomposition of at a constant volume: ( ) ( ) + ( ) / / 1 0 0.4 2 100 0.7 Calculate the rate constant. (Given: Log 4 = 0.6021, Log 2 =0.3010) Q36. Q37. (a) Complete the following chemical reaction equations: (i) ( ) + ( ) + +( ) (ii) ( ) + + ( ) + +( ) (b) (i) The gradual in size (actinoid contraction) from element to element is freater among the actinoids than that among the lanthanoids (lanthanoid contraction). (ii) The greatest number of oxidation state are exhibited u the members in the middle of a transition series. (iii) With the same d-orbitals configurations ( ) +ion is a reducing agent but +ion is an oxidizing agent. OR (a) How to you prepare: (i) ? (ii) ? (b) Account for the following: (i) + is more stable than + towards oxidation to + 3 state. (ii) The enthalpy of atomization is lowest for Zn in 3d series of the transition elements. (iii) Actinoids elements show wide range of oxidation states. An organic compound A with molecular formula C7H7NO reacts with Br2/aqKOH to give compound B , which upon reaction with NaNO2& HCl at O C gives C . Compound C on heating with CH3CH2OH gives a hydrocarbon D . Compound B on further reaction with Br2 water gives white precipitate of compound E . Identify the compound A, B, C, D&E; also justify your answer by giving relevant chemical equations. OR (a) How will you convert: (i) Aniline into Fluorobenzene. (ii) Benzamide into Benzylamine. (iii) Ethanamine to N,N-Diethylethanamine. (b) Distinguish between the following pair with suitable chemical reaction: (i) Aniline and Benzylamine. (ii) Methylamine and Dimethylamine.

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