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Class 12 ISC Board Exam 2018 : Chemistry Specimen Paper

6 pages, 78 questions, 53 questions with responses, 68 total responses,

Aiswarya Anil Nair
St. Thomas Residential School, Thiruvananthapuram

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CHEMISTRY PAPER 1 (THEORY) (Maximum marks: 70) (Time allowed: Three hours) (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 JK-1 mol-1 = 0 0821 dm3 atm K-1mol-1 1 l atm = 1 dm3 atm = 101 3 J. 1 Faraday = 96500 coulombs. Avogadro s number = 6 023 1023. --------------------------------------------------------------------------------------------------------------------Question 1 (a) Fill in the blanks by choosing the appropriate word/words from those given in the [4 1] brackets: (increases, decreases, efficient, same as, 68, non-efficient, greater than, 74, less than, sp3d3, sp3d2, octahedral, distorted octahedral, remains same) (i) Both ccp and hcp are ____________ close packing and occupy about _________% of the available space. (ii) The molar conductance of a solution _______________ with dilution, while its specific conductance _______________ with dilution. (iii) The geometry of XeF6 molecule is _____________ and the hybridization of Xe atom in the molecule is _______________. (iv) The acidic strength of phenol is ____________ ethyl alcohol but __________ nitro phenol. -------------------------------------------------------------------------------------------------------------------------1 ISC SPECIMEN QUESTION PAPER 2018 (b) Complete the choices given: (i) statements by selecting the correct alternative from the [4 1] [5] 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) (2) (3) (4) (ii) following -1 86oC -0 372oC -0 186oC +0 372oC Which among the following reacts fastest by SN2 reaction: (1) (CH3)3C Br (2) (CH3)2CH Br (3) CH3 CH2 Br (4) CH3 Br (iii) When acetaldehyde is treated with Grignard reagent followed by hydrolysis, the product formed is: (1) (2) (3) (4) Primary alcohol Secondary alcohol Carboxylic acid Tertiary alcohol (iv) Which of the following ores can be concentrated by froth floatation process: (1) Haematite (2) Calamine (3) Zinc blende (4) Bauxite (c) Match the following: [4 1] (i) Disaccharide (a) Adsorption (ii) Arrhenius equation (b) Condensation polymer (iii) Dacron (c) Activation energy (iv) Freundlich isotherm (d) Sucrose -------------------------------------------------------------------------------------------------------------------------2 ISC SPECIMEN QUESTION PAPER 2018 (d) Answer the following questions: [4 2] -1 (i) Calculate the mass of compound (molar mass = 256 g mol ) to be dissolved in 75 g of benzene to lower its freezing point by 0 48 K (Kf = 5 12 K kg mol-1). (ii) Write the IUPAC name of the complex [Cr(NH3)4Cl2]+. Which type of isomerism will be exhibited by it? (iii) Why do the transition elements have higher enthalpies of atomisation? In 3d series (Sc to Zn), which element has the lowest enthalpy of atomisation and why? (iv) Write balanced chemical equations for Carbylamine reaction and Diazotization reaction. Question 2 (a) [2] Identify the reaction order from each of the following rate constants: (i) k = 2 3 10-5 L mol-1 s-1. (ii) k = 3 10-4 s-1. OR (b) Write two differences between order of reaction and molecularity of reaction . Question 3 [2] (a) Differentiate between an antiseptic and a disinfectant. (b) Name a biodegradable detergent. Question 4 [2] What will be the major product obtained when 2-bromobutane reacts with alcoholic potassium hydroxide? State the type of reaction involved in it. Question 5 Write the names of the monomers of the following polymers: (a) Nylon-6 (b) Buna-N Question 6 [2] [2] Explain the amphoteric behaviour of amino acids. -------------------------------------------------------------------------------------------------------------------------3 ISC SPECIMEN QUESTION PAPER 2018 Question 7 [2] (a) How is phenol converted to benzoic acid? Explain with the help of balanced chemical equations. OR (b) Write the mechanism of acid dehydration of ethanol to yield ethene. Question 8 [2] 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 9 (a) (b) [3] Calculate the amount of CaCl2 (molar mass = 111 g mol-1) which must be added to 500 g of water to lower its freezing point by 2 K, assuming CaCl2 is completely dissociated. (Kf for water = 1.86 K kg mol-1). OR A solution containing 0 5 g of KCl dissolves in 100 g of water and freezes at 0 24o C. Calculate the degree of dissociation of the salt. (Kf for water = 1.86o C). Question 10 [3] An element with density 10 g cm-3 forms a cubic unit cell with edge length of 3 10 8 cm. What is the nature of the cubic unit cell if the atomic mass of the element is 81 g mol-1? Question 11 [3] Give reasons for the following observations: (a) Physisorption decreases with an increase in temperature. (b) Addition of alum purifies water. (c) Brownian movement stabilizes colloidal solutions. Question 12 (a) What type of isomers are [Co(NH3)5Br]SO4 and [Co(NH3)5SO4]Br.? Give a chemical test to distinguish between the two isomers. (b) Write the structures of optical isomers of the complex ion [Co(en)2Cl2]+ . Question 13 (a) [3] [3] Account for the following/Explain why: (i) Transition metals exhibit variable oxidation states. (ii) Zr (Z = 40) and Hf (Z = 72) have almost identical radii. (iii) Transition metals and their compounds act as a catalyst. -------------------------------------------------------------------------------------------------------------------------4 ISC SPECIMEN QUESTION PAPER 2018 OR (b) Complete the following chemical equations: (i) (ii) K2Cr2O7 + H2SO4 + FeSO4 K2Cr2O7 + H2SO4 + H2S (iii) KMnO4 + H2SO4 + H2C2O4 Question 14 [3] Arrange the following as directed: (a) Increasing order of basic strength: Aniline, p nitroaniline and p toluidine. (b) Decreasing order of basic strength in gas phase: C2H5NH2, (C2H5)2NH, (C2H5)3N and NH3. (c) Increasing order of solubility in water: C6H5NH2, (C2H5)2NH, C2H5NH2. Question 15 [3] How is silver extracted from its ore? Explain the process with relevant equations. Question 16 (a) (i) (ii) [5] Resistance of a conductivity cell filled with 0.1 mol L-1 KCl solution is 100 . If the resistance of the same cell when filled with 0 02 mol L-1 KCl solution is 520 , calculate the conductivity and molar conductivity of 0 02 mol L-1 KCl solution. The conductivity of 0 1 mol L-1 KCl solution is 1.29 10-2 -1cm-1. Define the following terms: (1) Limiting molar conductivity. (2) Fuel cell. OR (b) (i) Calculate emf of the following cell at 298 K: Mg(s) Mg2+ (0 1 M) Cu2+(0 01M) Cu(s) [Given Eocell = +2 71 V, 1 Faraday = 96500 C mol-1] (ii) State Faraday s first law of electrolysis. Calculate the charge required in terms of Faraday for the reduction of 1 mole of Cu2+ to Cu. -------------------------------------------------------------------------------------------------------------------------5 ISC SPECIMEN QUESTION PAPER 2018 Question 17 (a) (i) (ii) [5] Account for the following/Explain why: (1) Interhalogens are more reactive than halogens. (2) N2 is less reactive at room temperature. (3) Reducing character increases from NH3 to BiH3. Draw structures of the following: (1) H4P2O7 (2) XeF4 OR (b) (i) (ii) Account for the following/Explain why: (1) PCl5 exists but NCl5 does not. (2) Fluorine is a stronger oxidising agent than chlorine. (3) Bond enthalpy of F2 is less than that of Cl2. Complete and balance the following reactions: (1) FeSO4 + H2SO4 + Cl2 (2) P4 + HNO3 + + + Question 18 (a) (i) Write the product(s) of the following reactions: (1) CH3COCH3 + (2) 2 C6H5CHO + conc. NaOH CH3COOH Cl2/P (3) (ii) [5] H2NOH Give one chemical test each to distinguish between the following pairs of compounds: (i) Benzaldehyde and Benzoic acid (ii) Propanal and Propanone OR (b) (i) (ii) Write the chemical equations to illustrate the following name reactions: (1) Wolff-Kishner reduction. (2) Aldol condensation. (3) Cannizzaro reaction. Account for the following: (1) CH3CHO is more reactive with HCN than CH3COCH3. (2) Carboxylic acids are stronger acids than phenol. -------------------------------------------------------------------------------------------------------------------------6 ISC SPECIMEN QUESTION PAPER 2018

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