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Board Paper of Class 12-Science 2010 Chemistry Delhi(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

    Which point defect in crystals of a solid decreases the density of the solid?

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  • Question 3

    Give an example of ‘shape-selective catalyst’.

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  • Question 5

    Give an example of ionization isomerism.

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  • Question 6

    Give the IUPAC name of H2N − CH2 − CH2 − CH = CH2.

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  • Question 7

    A solution of KOH hydrolyses CH3CHClCH2CH3 and CH3CH2CH2Cl. Which one of these is more easily hydrolysed?

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  • Question 8

    Draw the structural formula of 1-phenylpropan-1-one molecule.

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  • Question 9

    Draw the structures of white phosphorus and red phosphorus. Which one of these two types of phosphorus is more reactive and why?

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  • Question 10

    The rate constant for a reaction of zero order in A is 0.0030 mol L−1 s−1. How long will it take for the initial concentration of A to fall from 0.10 M to 0.075 M?

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  • Question 11

    A reaction is of first order in reactant A and of second order in reactant Β. How is the rate of this reaction affected when (i) the concentration of B alone is increased to three times (ii) the concentrations of A as well as B are doubled?

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  • Question 12

    Non-ideal solutions exhibit either positive or negative deviations from Raoult’s law. What are these deviations and why are they caused? Explain with one example for each type.

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  • Question 13

    Explain the following observations:

    (i) Transition elements generally form coloured compounds.

    (ii) Zinc is not regarded as a transition element.

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  • Question 14

    How are the following conversions carried out?

    (i) Benzyl chloride to benzyl alcohol,

    (ii) Methyl magnesium bromide to 2-methylpropan-2-ol

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  • Question 15

    Illustrate the following reactions giving a chemical equation for each:

    (i) Kolbe’s reaction,

    (ii) Williamson synthesis.

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  • Question 16

    Explain the following terms:

    (i) Invert sugar

    (ii) Polypeptides

    OR

    Name the products of hydrolysis of sucrose. Why is sucrose not a reducing sugar?

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  • Question 17

    Name the following coordination compounds according to IUPAC system of nomenclature:

    (i) [Co(NH3)4 (H2O)Cl] Cl2

    (ii) [CrCl2 (en)2] Cl, (en = ethane − 1, 2 − diamine)

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  • Question 18

    State clearly what are known as nucleosides and nucleotides.

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  • Question 19

    The density of copper metal is 8.95 g cm−3. If the radius of copper atom is 127.8 pm, is the copper unit cell a simple cubic, a body-centred cubic or a face centred cubic structure? (Given: At. Mass of Cu = 63.54 g mol−1 and NA = 6.02 × 1023 mol−1)

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  • Question 20

    How are the following colloids different from each other in respect of their dispersion medium and dispersed phase? Give one example of each.

    (i) Aerosol

    (ii) Emulsion

    (iii) Hydrosol

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  • Question 21

    A solution prepared by dissolving 1.25 g of oil of winter green (methyl salicylate) in 99.0 g of benzene has a boiling point of 80.31 °C. Determine the molar mass of this compound. (B.P. of pure benzene = 80.10 °C and Kb for benzene = 2.53 °C kg mol−1)

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  • Question 22

    Describe how the following changes are brought about:

    (i) Pig iron into steel

    (ii) Zinc oxide into metallic zinc

    (iii) Impure titanium into pure titanium.

    OR

    Describe the role of

    (i) NaCN in the extraction of gold from gold ore.

    (ii) SiO2 in the extraction of copper from copper matte.

    (iii) Iodine in the refining of zirconium.

    Write chemical equations for the involved reactions.

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  • Question 23

    (i) State oneuseeach of DDT and iodoform.

    (ii) Which compound in the following couples will react faster in SN2 displacement and why?

    (a) 1-Bromopentane or 2-bromopentane

    (b) 1-bromo-2-methylbutane or 2-bromo-2-methylbutane.

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  • Question 24

    How would you account for the following?

    (i) The atomic radii of the metals of the third (5d) series of transition elements are virtually the same as those of the corresponding members of the second (4d) series.

    (ii) The E° Value for the Mn3+/Mn2+ couple is much more positive than that for Cr3+/Cr2+ couple or Fe3+/Fe2+ couple.

    (iii) The highest oxidation state of a metal is exhibited in its oxide or fluoride.

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  • Question 25

    In the following cases rearrange the compounds as directed:

    (i) In an increasing order of basic strength:

    C6H5NH2,C6H5 N (CH3)2, (C2H5)2 NH and CH3NH2

    (ii) In a decreasing order of basic strength:

    Aniline, p-nitroaniline and p-toluidine

    (iii) In an increasing order of pKb values:

    C2H5NH2, C6H5 NHCH3, (C2H5)2 NH and C6H5NH2

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  • Question 26

    Differentiate between thermoplastic and thermosetting polymers. Give one example of each.

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  • Question 27

    Explain the following terms with one suitable example in each case.

    (i) Cationic detergents

    (ii) Enzymes

    (iii) Antifertility drugs

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  • Question 28

    (a) Explain the mechanism of a nuclophilic attack on the carbonyl group of an aldehyde or a ketone.

    (b) An organic compound (A) (molecular formula C8H16O2) was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid also produced (B). On dehydration (C) gives but-1-ene. Write the equations for the reactions involved.

    OR

    (a) Give chemical tests to distinguish between the following pairs of compounds:

    (i) Ethanal and Propanal

    (ii) Phenol and Benzoic acid

    (b) How will you bring about the following conversions?

    (i) Benzoic acid to benzaldehyde

    (ii) Ethanal to but-2-enal

    (iii) Propanone to propene

    Give complete reaction in each case.

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  • Question 29

    (a) State Kohlrausch law of independent migration of ions. Write an expression for the molar conductivity of acetic acid at infinite dilution according to Kohlrausch law.

    (b) Calcualte for acetic acid.

    Given that (HCl) = 426 S cm2 mol−1

    (NaCl) = 126 S cm2 mol−1

    (CH3COONa) = 91 S cm2 mol−1

    OR

    (a) Write the anode and cathode reactions and the overall reaction occurring in a lead storage battery.

    (b) A copper-silver cell is set up. The copper ion concentration is 0.10 M. The concentration of silver ion is not known. The cell potential when measured was 0.422 V. Determine the concentration of silver ions in the cell. (Given)

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  • Question 30

    (a) Complete the following chemical equations:

    (b) How would you account for the following?

    (i) The value of electron gain enthalpy with negative sign for sulphur is higher than that for oxygen.

    (ii) NF3 is an exothermic compound but NCl3 is endothermic compound.

    (iii) ClF3 molecule has a T-shaped structure and not a trigonal planar one.

    OR

    (a) Complete the following chemical reaction equations:

    (i) P4 + SO2Cl2

    (ii) XeF4 + H2O →

    (b) Explain the following observations giving appropriate reasons:

    (i) The stability of + 5 oxidation state decreases down the group in group 15 of the periodic table.

    (ii) Solid phosphorus pentachloride behaves as an ionic compound.

    (iii) Halogens are strong oxidizing agents.

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