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CBSE Class 12 Pre Board 2019 : Chemistry - Prelim 1 (St Xavier's Sr. Sec. School, Delhi)

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Pre Board Examination 2019 Std. 12 21-01-2019 Set 1 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. Examine the given defective crystal : X+ YX+ Y- YX+ YX+ X+ YX+ Y- Y- X+ X+ Ye- X+ X+ Y- a) b) Is the above defect stoichiometric or non-stoichiometric? Write the term used for the electron occupied sites. (OR) There is an increase in conductivity when silicon is doped with phosphorous. Give reason. (1) 2. Of physisorption and chemisorption, which type of adsorption has a higher enthalpy of adsorption? 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) Which of the following is a more stable complex and why? 3+ 3+ [Co(NH3)6 ] and [Co(en)3 ] (1) 4. Identify the compound which on hydrogenation produces an optically active compound from the following compounds: (1) 5. Write the structure of the product obtained when glucose is oxidised with nitric acid. (1) (1) 4 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 (OR) Write the structures and IUPAC names of cross aldol condensation products only of ethanal and propanal. (2)

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