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Board Paper of Class 12-Science 2011 Chemistry (SET 3) - Solutions

General Instructions:
(i) All questions are compulsory
(ii) Question numbers 1 to 8 are very short-answer questions and carry 1 mark each.
(iii) Question numbers 9 to 18 are short-answer questions and carry 2 marks each.
(iv) Question numbers 19 to 27 are also short-answer questions and carry 3 marks.
(v) Question numbers 28 to 30 are long-answer questions and carry 5 marks each.
(vi) Use Log Tables, if necessary. Use of calculators is not allowed.
  • Question 1

    Define ‘activation energy’ of a reaction.

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  • Question 2

    What is meant by ‘reverse osmosis’?

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  • Question 3

    What type of ores can be concentrated by magnetic separation method?

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  • Question 4

    Write the IUPAC name of the following compound: CH2 = CHCH2Br

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  • Question 5

    What is meant by ‘lanthanoid contraction’?

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  • Question 6

    How would you convert ethanol to ethene?

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  • Question 7

    Draw the structure of 4-chloropentan-2-one.

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  • Question 8

    Give a chemical test to distinguish between ethylamine and aniline.

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  • Question 9

    Calculate the packing efficiency of a metal crystal for a simple cubic lattice.

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  • Question 10

    Explain how you can determine the atomic mass of an unknown metal if you know its mass density and the dimensions of unit cell of its crystal.

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  • Question 11

    Differentiate between molarity and molality values for a solution. What is the effect of change in temperature on molarity and molality values?

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  • Question 12

    The thermal decomposition of HCO2H is a first order reaction with a rate constant of 2.4 × 10−3 s−1 at a certain temperature. Calculate how long will it take for three-fourths of initial quantity of HCO2H to decompose.

    (log 0.25 = − 0.6021)

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  • Question 13

    What do you understand by the rate law and rate constant of a reaction?

    Identify the order of a reaction if the units of its rate constant are:

    (i) L−1 mol s−1

    (ii) L mol−1 s−1

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  • Question 14

    Describe the principle controlling each of the following processes:

    (i) Preparation of cast iron form pig iron.

    (ii) Preparation of pure alumina (Al2O3) from bauxite ore.

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  • Question 15

    Explain giving reasons:

    (i) Transition metals and their compounds generally exhibit a paramagnetic behaviour.

    (ii) The chemistry of actinoids is not so smooth as that of lanthanoids.

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  • Question 16

    Complete the following chemical equations:

    (i)

    (ii)

    OR

    State reasons for the following:

    (i) Cu (I) ion is not stable in an aqueous solution.

    (ii) Unlike Cr3+, Mn2+, Fe3+ and the subsequent other M2+ ions of the 3d series of elements, the 4d and the 5d series metals generally do not form stable cationic species.

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  • Question 17

    Write the main structural difference between DNA and RNA. Of the four bases, name those which are common to both DNA and RNA.

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  • Question 18

    Write such reactions and facts about glucose which cannot be explained by its open chain structure.

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  • Question 19

    A solution prepared by dissolving 8.95 mg of a gene fragment in 35.0 mL of water has an osmotic pressure of 0.335 torr at 25°C.

    Assuming that the gene fragment is a non-electrolyte, calculate its molar mass.

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  • Question 20

    Classify colloids where the dispersion medium is water. State their characteristics and write an example of each of these classes.

    OR

    Explain what is observed when

    (i) an electric current is passed through a sol

    (ii) a beam of light is passed through a sol

    (iii) an electrolyte (say NaCl) is added to ferric hydroxide sol

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  • Question 21

    How would you account for the following:

    (i) NF3 is an exothermic compound but NCl3 is not.

    (ii) The acidic strength of compounds increases in the order:

    PH3 < H2S < HCl

    (iii) SF6 is kinetically inert.

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  • Question 22

    Write the state of hybridization, the shape and the magnetic behaviour of the following complex entities:

    (i) [Cr(NH3)4 Cl2] Cl

    (ii) [Co(en)3] Cl3

    (iii) K2 [Ni(CN)4]

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  • Question 23

    State reasons for the following:

    (i) pKb value for aniline is more than that for methylamine.

    (ii) Ethylamine is soluble in water whereas aniline is not soluble in water.

    (iii) Primary amines have higher boiling points than tertiary amines.

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  • Question 24

    Rearrange the compounds of each of the following sets in order of reactivity towards SN2 displacement:

    (i) 2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane

    (ii) 1-Bromo-3-methylbutane, 2-Bromo-2-methylbutane, 3-Bromo-2-methylbutane

    (iii) 1-Bromobutane, 1-Bromo-2, 2-dimethylpropane, 1-Bromo-2-methylbutane

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  • Question 25

    How would you obtain the following:

    (i) Benzoquinone from phenol

    (ii) 2-methyl propan-2-ol from methyl-magnesium bromide

    (iii) Propane-2-ol from propene

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  • Question 26

    Write the names and structures of the monomers of the following polymers:

    (i) Buna-S

    (ii) Dacron

    (iii) Neoprene

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  • Question 27

    What are the following substances? Give one example of each.

    (i) Food preservatives

    (ii) Synthetic detergents

    (iii) Antacids

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  • Question 28

    (a) Draw the structures of the following molecules:

    (i) (HPO3)3

    (ii) BrF3

    (b) Complete the following chemical equations:

    (i) HgCl2 + PH3

    (ii) SO3 + H2SO4

    (iii) XeF4 + H2O →

    OR

    (a) What happens when

    (i) chlorine gas is passed through a hot concentrated solution of NaOH?

    (ii) sulphur dioxide gas is passed through an aqueous solution of a Fe (III) salt?

    (b) Answer the following:

    (i) What is the basicity of H3PO3 and why?

    (ii) Why does fluorine not play the role of a central atom in inter-halogen compounds?

    (iii) Why do noble gases have very low boiling points?

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  • Question 29

    (a) What type of a battery is lead storage battery? Write the anode and cathode reactions and the overall cell reaction occurring in the operation of a lead storage battery.

    (b) Calculate the potential for half-cell containing 0.10 M K2Cr2O7 (aq), 0.20 M Cr3+ (aq) and 1.0 × 10−4 M H+ (aq)

    The half-cell reaction is and the standard electrode potential is given as E0 = 1.33 V.

    OR

    (a) How many moles of mercury will be produced by electrolysing 1.0 M

    Hg (NO3)2 solution with a current of 2.00 A for 3 hours?

    [Hg(NO3)2 = 200.6 g mol−1]

    (b) A voltaic cell is set up at 25°C with the following half-cells Al3+ (0.001 M) and Ni2+ (0.50 M). Write an equation for the reaction that occurs when the cell generates an electric current and determine the cell potential.

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  • Question 30

    (a) Illustrate the following name reactions:

    (i) Cannizzaro’s reaction

    (ii) Clemmensen reduction

    (b) How would you obtain the following:

    (i) But-2-enal from ethanal

    (ii) Butanoic acid from butanol

    (iii) Benzoic acid from ethylbenzene

    OR

    (a) Given chemical tests to distinguish between the following:

    (i) Benzoic acid and ethyl benzoate

    (ii) Benzaldehyde and acetophenone

    (b) Complete each synthesis by giving missing reagents or products in the following:

    (i)

    (ii)

    (iii)

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