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GOLDCREST HIGH-LATUR ON THE WINGS OF EXCELLENCE PRELIMINARY EXAMINATION SUBJECT:- CHEMISTRY PAPER-1 (THEORY) TIME:- 3 HOURS DATE:-21.12.2017 GRADE: XII MARKS: 70 General Instructions (Candidates are allowed additional 15 minutes for only reading the paper. They must NOT start writing during this time) --------------------------------------------------------------------------------------------------------------------All questions are compulsory Question 1 is of 20 marks having four sub parts, all of which are compulsory. Question numbers 2 to 8 carry 2 marks each, with any two questions having internal choice. Question numbers 9 to 15 carry 3 marks each, with any two questions having an internal choice. Question numbers 16 to 18 carry 5 marks each, with an internal choice. All working, including rough work, should be done on the same sheet as, and adjacent to the rest of the answer. The intended marks for questions or parts of questions are given in brackets [ ]. Balanced equations must be given wherever possible and diagrams where they are helpful. When solving numerical problems, all essential working must be shown. In working out problems, use the following data: Gas constant R = 1.987 cal deg-1 mol-1 = 8.314 J K-1 mol-1 = 0.0821 dm3 atm K-1 mol-1 1 L atm = 1 dm3atm = 101.3 J 1 Faraday = 96500 coulombs. Avogadro s number = 6.023 x 1023 Question:-1 (a) Fill in the blanks by choosing the word /words from those given in the brackets: [4 x 1=4] (increases, decreases, 68,efficient, cubic,less than, zero,sp3d2 small, , 54,atoms, unpaired,sp3d,pentagonal bipyramidal, 74, more, d2 sp3 greater than, octahedral) (i)The Van t Hoff factor of acetic acid solution is _____than one and the value of normal colligative property is _______ than the observed colligative property of this solution. (ii) The acidic strength of phenol is_____ ethyl alcohol but_____ nitro phenol. (iii) Both ccp and hcp are _____ close packing and occupy about____ % of available space. (iv) SF6 has _____ hybridization and _____ structure (b)Complete the following statements by choosing the correct alternative from the choices given: [4 x 1=4] (i) The molal freezing point constant of water is 1.86 K Kg mol-1.Therefore, the freezing point of 0.1M NaCl solution in water is expected to be : (1)-1.86 oC (2) -0.372 oC (3) -0.186 oC (4) +0.372 oC (ii) For the first order reaction the rate constant for decomposition of N2O5 is 6 x 10-4 Sec -1.The half life period for the decomposition in seconds is: (1)11.55 (2)115.5 (3)1155 (4) 1.155 (iii)When acetaldehyde is treated with Grignard reagent, followed by hydrolysis the product formed is : (1)Primary alcohol (2) Secondary alcohol (3) Carboxylic acid (4) Tertiary alcohol (iv) In the complexs [Fe (CN)6]3- and [Pt(en)(H2O)2(NO2)(Cl)]2+ the respective oxidation numbers of central metal atoms are : (1) +3 and +4 (2) +6 and +4 (3)+6 and +3 (4) +3 and +3 Page 1 of 6 (c) Match the following: [4 x 1=4] (i) Specific conductivity (a) Argentite (ii)Froth flotation process (b) Thermosetting plastics (iii)Aniline (c) Polytetraflurorthene (iv)Bakelite (d) Ohm-1cm-1 (e) Diazotisation (d)Answer the following questions: [4 x 2=8] (i)What is Metal excess defect in solid crystal? The radius of Na+ ion is 95 pm and that of Cl- ion is 181 pm . Predict the coordination number of Na+ ion (ii) (a) SF6 exists but OF6 does not, though both oxygen and sulphur belong to Group 16 in the Periodic table. (b) [NiCl4] 2 is paramagnetic while [Ni(CO)4] is diamagnetic though both are tetrahedral. Why (iii) (a)Write the formula of the following compounds: (i) Triamminetriaquachromium(III)chloride (ii) Potassiumhexacyanoferrate(III) (b) Calculate the equivalent conductivity of 1 M H2SO4,whose specific conductivity is 26 x 10-2 ohm-1 cm-1. (iv) How will you distinguish between : (i)Acetone and Phenol (Chemical Test) (ii) Carbylamine reaction and Sandmeyer s reaction (Chemical Reaction) Question-2 [2] (a) A reactant has a half-life of 10 minutes. (i) Calculate the rate constant for the first order.(ii) What fraction of the reactant will be left after an hour of the reaction has occurred.? OR (b) A substance decomposes by following first order kinetics. If 50% of the compound is decomposed in 120 minutes, how long will it take for 90% of the compound to decompose? Question-3 [2] (a) With the help of chemical equations show how will you convert: (i) Methyl bromide to acetic acid (ii) chlorobenzene to toluene (b) Define Zwitter Ion with the help of structure of amino acids Page 2 of 6 Question-4 [2] (a) How is phenol converted to benzoic acid? Explain with the help of balanced chemical equations (b) Write the mechanism of acid dehydration of ethanol to yield ethene. . Question-5 [2] (a) Write the names of the monomers of the following polymers: (i) Nylon-6 (b) What are thermoplastic and thermosetting plastics? Give one example of each kind (ii) Buna-N Question-6 [2] Write one chemical equation for each, to illustrate the following reactions: a) Rosenmund reduction b) Carbylamine reaction Question-7 [2] (a) Give suitable chemical test to distinguish between Primary ,Secondary, Tertiary Amines with Hinsberg s reagent OR (b) Distinguish between Primary, Secondary and Tertiary alcohol by Lucas test Question-8 [2] An element with molar mass 27 g mol-1 forms a cubic unit cell with edge length 4.05 x 10-8 cm. Its density is 2.7 g cm -3, what is the nature of the cubic unit cell. Question-9 [3] (a) At 250C the osmotic pressure of a solution of an organic substance containing 1.425g per 100 ml of water was found to be 760 mm of Hg. Calculate the molecular the weight of the substance.(R=0.082) (b) The freezing point of nitrobenzene is 278.8K.A 0.25 molal solution of a substance (molal mass = 120) in nitrobenzene has a freezing point of 278.K .Calculate its molal depression constant of nitrobenzene OR (c) Albumins are the most abundant proteins in the blood. At 250C , 3.5 g of albumin in 100 ml of water produces an osmotic pressure of 0.014 atms. What is the molecular weight of albumin? (d) The cryoscopic constant of water is 1.86 K mol-1kg. An aqueous solution of cane sugar freezes at -0.372 o C. Calculate the molality of the solution. Page 3 of 6 Question-10 [3] The experimental data for the reaction : 2A + B2 2AB, are as follows. Write probable rate expression. [A] mol/L 1 [B2] mol/L 1 Initial rate (mol L 1 sec 1) 1.0 1.0 2.0 x 10-3 2.0 1.0 4.0 x 10-3 4.0 1.0 8.0 x 10-3 1.0 2.0 2.0 x 10-3 1.0 4.0 2.0 x 10-3 (i) What are the orders with respect to A and B? (ii) What is the overall order? (iii) Write the rate law equation. (iv) Calculate the rate constant Question-11 [3] (a) What is Frendulich adsorption isotherm? (b) Give reason for the following: (i) Artificial rain is caused by spraying salt over clouds (ii) Why are lyophilic sols more stable than lyophobic colloidal sols? Question-12 [3] (a) Indicate the types of isomerism exhibited by the following complexes: (i) K[Cr(H2O)2(C2O4)2 (ii) [Co(en)3]Cl3 (iii) [Co(NH3)5(NO2)](NO3)2 (iv) [Co(NH3)5Br]SO4 and [Co(NH3)5SO4]Br (b) State the hybridization, geometry and draw the structure of the following: XeOF4 Question-13 [3] (a) Describe the oxidising action of potassium dichromate and write the ionic equations for its reaction with: (i) iodide (ii) SO2 (iii) H2S (iv) ferrous sulfate solution (b) In a given transition series, there is no significant change in the atomic radii of elements with increase in atomic number. Explain why? OR (c) How does the acidified permanganate solution react with : Write the ionic equations for the reactions (i) iron(II) ions (ii) SO2 (iii) oxalic acid (iv) H2S (d) How would you account for the following: Among lanthanoids, Ln compounds are predominant. However occasionally in solutions or in solid compounds, +2 and +4 are also obtained. Page 4 of 6 Question-14 [3] An organic compound A with molecular formula C7H8 on oxidation by chromylchloride in the presence of CCl4 gives a compound B which gives positive tollen s test. The compound B on treatment with NaOH followed by acid hydrolysis gives two products C and D. C on oxidation gives B which on further oxidation gives D. The compound D on distillation with soda lime gives a hydrocarbon E. Below 60oC, concentrated nitric acid reacts with E in the presence of concentrated sulphuric acid forming a compound F. Identify the compounds A, B, C, D, E and F and write the balanced reaction for the conversion of A to F Question-15 [3] Copper pyrites is an ore of copper. (i) Describe the process by which copper pyrites is concentrated (ii) Describe all the steps with equations to convert the concentrated ore to blister copper. (iii) Describe the process of conversion of blister copper to pure copper Question-16 [5] (a) A current of 10 A is passed for 80 min and 27 seconds through the a cell containing dilute H2SO4 .(i) How many moles of oxygen gas will be liberated at the anode? (ii) Calculate the amount of zinc deposited at the cathode when another cell containing ZnSO4 soln. connected in series.(Zn=65). (b) (i) A solution of 0.1 N KCl offers a resistance of 245 ohms. Calculate the specific conductance and the equivalent conductance of the solution if the cell constant is 0.571cm-1 (ii) Define molar conductance of a solution. State its unit. How is it related to the specific conductance of a solution? OR (c) (i) Calculate the maximum work done that can be obtained from the given electrochemical cell constructed with two metals M and N . [Eo M2+/M = -0.76 V ; Eo N2+/N =0.34 V]. (ii)How many electrons will flow when a current of 5 amperes is passed through a solution for 200 seconds. (d) (i) Write Nernst Equation and compute the e.m.f of the following cell at 298K: Sn(s)/Sn2+(0.5M) || H+(0.02M) / H2, 1 atm, Pt [Given E0 Sn2+/Sn= -0.136 V] (ii) Give a reason for the following Specific conductance decreases with dilution whereas equivalent conductance increases with dilution Page 5 of 6 Question-17 [5] (a) Account for the following/Explain why: (i)PCl5 exists but NCl5 does not. (ii)Fluorine is a stronger oxidising agent than chlorine. (iii)Bond enthalpy of F2 is less than that of Cl2. (b) Complete and balance the following reactions: (i) FeSO4 + H2SO4 + Cl2 ________ +________ (ii) P4 + HNO3 ________ + _________ +________ OR (c) Account for the following/Explain why: (i) Inter halogens are more reactive than halogens. (ii)N2 is less reactive at room temperature. (iii) Reducing character increases from NH3 to BiH3. (d) Draw structures of the following: (i)H4P2O7 (ii) XeF4 Question-18 [5] (a) Write the chemical equations to illustrate the following name reactions: (i) Clemmensen s reduction. (ii) Kolbe s electrolytic reaction. (iii)Balz-Schiemann s reaction. (b) Give one chemical test each to distinguish between the following pairs of compounds: (i) Benzaldehyde and Benzoic acid (ii) Propanal and Propanone OR (c) Give balanced equations for the following name reactions: (i) Wolff-Kishner reduction. (ii) Benzoin Condensation (iii)Cannizzaro reaction. (d) Identify the reagents A, B, C, D, required for the following conversion: ------------------------------------END------------------------------------------Page 6 of 6
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