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## ISC Chemistry 2013 Class-12 Previous Year Question Paper Solved

-: Select Options :-

Part – I

Part – II Section – A

Part – II Section – B

Part – II Section – C

Maximum Marks: 70
Time allowed: 3 hours

• Answer all questions in Part I and six questions from Part II, choosing two questions from Section A, two from Section B and two from Section C.
• 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-1 mol-1. 1L atm = 1 dm3 atm = 101.3 J.
1 Faraday = 96500 Coulombs, Avogadro’s number = 6.023 × 1023

### Part – I (20 Marks)(Answer all questions)

ISC Chemistry 2013 Class-12 Previous Year Question Paper Solved

Question 1.
(a) Fill in the blanks by choosing the appropriate word/words from those given in the brackets: [5] (zero, first, second, increased, decreased, anode, cathode, active, inactive, potassium cyanide, internal, external, dependent, independent, red, benzoic acid, benzoin, common ion effect, salt hydrolysis, alkali, potassium hydroxide.)
(i) In a galvanic cell, electrons flow from ………. to ……….. through the connecting wires.
(ii) Racemic mixtures are optically …………. because of …………… compensation.
(iii) The half-life period of a …………. order reaction is …………. of the concentration of the reactant.
(iv) Benzaldehyde when treated with an alcoholic solution of ……… forms ………..
(v) The solubility of calcium oxalate is …………. in the presence of ammonium oxalate because of ……….

(b) Complete the following statements by selecting the correct alternative from the choices given: [5] (i) The compound which is optically active is:
(1) 1-butanol
(2) 2-butanol
(3) 1-propanol
(4) 2-methyl-l-propanol

(ii) The salt which will not hydrolyse in aqueous solution is:
(1) Copper sulphate
(2) Sodium sulphate
(3) Potassium cyanide
(4) Sodium carbonate

(iii) Copper has the face centred cubic structure. The coordination number of each ion is:
(1) 4
(2) 12
(3) 14
(4) 8

(iv) For the reaction $2 \mathrm{SO}_{2}+\mathrm{O}_{2} \rightleftharpoons 2 \mathrm{SO}_{3}$ the unit of equilibrium constant is:
(1) L mol-1
(2) J mol-1
(3) mol L-1
(4) [L mol-1]2

(v) The deficiency of vitamin D causes:
(1) Rickets
(2) Gout
(3) Scurvy
(4) Night blindness

(c) Answer the following questions: [5]
(i) Two metallic elements A and B have the following standard oxidation potentials:
A = 0.40 V, B = -0.80 V. What would you expect if element A was added to an aqueous salt solution of element B? Give a reason for your answer.
(ii) Two moles of NH3 are introduced into the one-litre flask in which it dissociates at high temperature as follows:
$2 \mathrm{NH}_{3}(g) \rightleftharpoons \mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g)$
Determine Kc if at equilibrium 1 mole of NH3 remains.
(iii) Give a balanced equation for the preparation of salicylaldehyde from phenol.
(iv) If the half-life period for a first-order reaction is 69.3 seconds, what is the value of its rate constant?
(v) Define cryoscopic constant.

(d) Match the following: [5]

 (i) Colligative property (a) Polysaccharide (ii) Nicol prism (b) Osmotic pressure (iii) Activation energy (c) Aldol condensation (iv) Starch (d) Polarimeter (v) Acetaldehyde (e) Arrhenius equation

(a)

(i) anode, cathode
(ii) inactive, external
(iii) first, independent
(iv) potassium cyanide, benzoin
(v) decreased, common ion effect

(b)

(i) (2) 2-butanol
(ii) (2) Sodium sulphate
(iii) (2) 12
(iv) (1) L mol-1
(v) (1) Rickets

(c)

(i) Since the oxidation potential of A is higher than that of B, therefore, metal A will displace metal B from its salt solution.

(v) Cryoscopic constant: It is defined as the depression in freezing point of the solvent produced on dissolving one mole of a substance in 1000 g of it. It is also called molal depression constant.

(d)

(i) Colligative property → (b) Osmotic pressure
(ii) Nicol prism → (d) Polarimeter
(iii) Activation energy → (e) Arrhenius equation
(iv) Starch → (a) Polysaccharide
(v) Acetaldehyde → (c) Aldol condensation

### Part – II (50 Marks)

A nswer six questions choosing two from Section A, two from Section B and two from Section C.

Section – A
(Answer any two questions)

ISC Chemistry 2013 Class-12 Previous Year Question Paper Solved

Question 2.
(a)

(i) Ethylene glycol is used as an antifreeze agent. Calculate the amount of ethylene glycol to be added to 4 kg of water to prevent it from freezing at -6°C. (Kf for H2O = 1.85 K mole-1 kg) [3] (ii) The freezing point of a solution containing 0.3 g of acetic acid in 30 g of benzene is lowered by 0.45 K. Calculate the Van’t Hoff factor.
(at. wt. of C = 12, H = 1, O = 16, Kf for benzene = 5.12 K kg mole-1) [2] (b) Name the law or principle confirmed by the following observations:
(i) When water is added to 0.01 M aqueous solution of acetic acid the number of hydrogen ions increase. [2] (ii) When 96500 coulombs of electricity is passed through acidulated water, 5.6 litres of oxygen at s.t.p. is liberated at the anode. [1] (c) Arrange Ag, Cr and Hg metals in the increasing order of reducing power. Given: [1]

(d) In a first-order reaction, 10% of the reactant is consumed in 25 minutes. Calculate: [2]
(i) The half-life of the reaction.
(ii) The time required for completing 17% of the reaction.

Question 3.
(a) Explain giving reasons why (Give equations in support of your answer):
(i) A solution of NH4Cl and NH4OH acts as a buffer. [2] (ii) Cu is precipitated as CuS while Zn is not precipitated when H2S is passed through an acidic solution of Cu(NO3)2 and Zn(NO3)2 respectively. [2] (b)

(i) What is Schottky defect in a solid? [1] (ii) A bcc element (atomic mass 65) has a cell edge of 420 pm. Calculate its density in g/cm3 [3] (c) The rate of the reaction $\mathrm{H}_{2}+\mathrm{I}_{2} \rightleftharpoons 2 \mathrm{HI}$ is given by:
Rate = 1.7 × 10-19 [H2] [I2] at 25°C. [2] The rate of decomposition of gaseous HI to H2 and I2 is given by:
Rate = 2.4 × 10-21 [HI]2 at 25°C.
Calculate the equilibrium constant for the formation of HI from H2 and I2 at 25°C. [2] Answer 3:
(a)

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