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Board Paper of Class 12-Science 2008 Chemistry Delhi(SET 1) - 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

    What is the coordination number of each type of ions in a rock-salt type crystal structure?

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  • Question 2

    Define the term ‘order of reaction’ for chemical reactions.

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  • Question 3

    What causes Brownian movement in a colloidal solution?

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  • Question 4

    In which one of the two structures, and , the bond angle has a higher

    value? 

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  • Question 5

    Write the IUPAC name of the following compound:

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  • Question 6

    Arrange the following compounds in an increasing order of their acid strengths:

    (CH3)2CHCOOH, CH3CH2CH(Br)COOH, CH3CH(Br)CH2COOH

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  • Question 7

    Write a chemical reaction in which the iodide ion replaces the diazonium group in a diazonium salt.

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  • Question 8

    Name a substance that can be used as an antiseptic as well as a disinfectant.

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  • Question 9

    Explain as to why haloarenes are much less reactive than haloalkanes towards nucleophilic substitution reactions.

    OR

    Which compound in each of the following pairs will react faster in SN2 reaction with −OH? Why?

    (i) CH3Br or CH3I

    (ii) (CH3)3CCl or CH3Cl

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  • Question 10

    (a) State the IUPAC name of the following compound:

    (b) Complete the following chemical equation:

    CH3CH2CH=CH2 + HBr

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  • Question 11

    State Henry’s law correlating the pressure of a gas and its solubility in a solvent and mention two applications for the law.

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  • Question 12

    A first order decomposition reaction takes 40 minutes for 30% decomposition. Calculate its value.

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  • Question 13

    What is meant by the ‘rate constant, k’ of a reaction? If the concentration be expressed in mol L−1 units and time in seconds, what would be the units for k (i) for a zero-order reaction and (ii) for a first-order reaction?

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  • Question 14

    Define the following terms in relation to proteins:

    (i) Peptide linkage

    (ii) Denaturation

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  • Question 15

    List the reactions of glucose which cannot be explained by its open-chain structure.

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  • Question 16

    Assign a reason for each of the following statements:

    (i) Ammonia is a stronger base than phosphine.

    (ii) Sulphur in vapour state exhibits a paramagnetic behaviour.

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  • Question 17

    Draw the structure of the following molecules:

    (i) SF4

    (ii) XeF4

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  • Question 18

    What are biodegradable and non-biodegradable detergents? Give one example of each class.

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  • Question 19

    What is semiconductor? Describe the two main types of semiconductors and explain mechanisms for their conduction.

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  • Question 20

    Calculate the temperature at which a solution containing 54 g of glucose, (C6H12O6), in 250 g of water will freeze.

    (Kf for water = 1.86 K mol−1 kg)

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  • Question 21

    What are lyophilic and lyophobic sols? Give one example of each type. Which one of these two types of sols is easily coagulated and why?

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  • Question 22

    State briefly the principles which serve as basis for the following operations in metallurgy:

    (i) Froth floatation process

    (ii) Zone refining

    (iii) Refining by liquation

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  • Question 23

    Write chemical equations for the following processes:

    (i) Chlorine reacts with a hot concentrated solution of sodium hydroxide

    (ii) Orthophosphorous acid is heated

    (iii) PtF6 and xenon are mixed together

    OR

    Complete the following chemical equations:

    (i) Ca3P2(s) + H2O(l) ……..

    (iii) F2(g) + H2O(l) ……..

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  • Question 24

    (a) What is a ligand? Give an example of a bidentate ligand.

    (b) Explain as to how the two complexes of nickel, [Ni(CN)4]2− and Ni(CO)4, have different structures but do not differ in their magnetic behaviour. (Ni = 28)

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  • Question 25

    Name the reagents which are used in the following conversions:

    (i) A primary alcohol to an aldehyde

    (ii) Butan-2-one to butan-2-ol

    (iii) Phenol to 2, 4, 6-tribromophenol

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  • Question 26

    Account for the following observations:

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

    (ii) Methylamine solution in water reacts with ferric chloride solution to give a precipitate of ferric hydroxide.

    (iii) Aniline does not undergo Friedel-Crafts reaction.

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  • Question 27

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

    (i) Buna-S

    (ii) Neoprene

    (iii) Nylon-6

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  • Question 28

    Conductivity of 0.00241 M acetic acid solution is 7.896 × 10−5 S cm−1. Calculate its molar conductivity in this solution. If for acetic acid be 390.5 S cm2 mol−1, what would be its dissociation constant?

    OR

    Three electrolytic cells A, B and C containing solutions of zinc sulphate, silver nitrate and copper sulphate respectively, are connected in series. A steady current of 1.5 ampere was passed through them until 1.45 g of silver was deposited at the cathode of cell B. How long did the current flow? What mass of copper and what mass of zinc were deposited in the concerned cells?

    (Atomic masses of Ag = 108, Zn = 65.4, Cu = 63.5)

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  • Question 29

    Assign reasons for the following:

    (i) The enthalpies of atomisation of transition elements are high.

    (ii) The transition metals and many of their compounds act as good catalyst.

    (iii) From element to element the actinoid contraction is greater than the lanthanoid contraction.

    (iv) The E0 value for the Mn3+/Mn2+ couple is much more positive than that for Cr3+/Cr2+.

    (v) Scandium (Z = 21) does not exhibit variable oxidation states and yet it is regarded as a transition element.

    OR

    (a) What may be the possible oxidation states of the transition metals with the following d electronic configurations in the ground state of their atoms:

    3d34s2, 3d54s2 and 3d64s2

    Indicate relative stability of oxidation states in each case.

    (b) Write steps involved in the preparation of (i) Na2CrO4 from chromite ore and (ii) K2MnO4 from pyrolusite ore.

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  • Question 30

    (a) Complete the following reaction statements by giving the missing starting material, reagent or product as required:

    (i)

    (ii)

    (iii)

    (b) Describe the following reactions:

    (i) Cannizaro reaction

    (ii) Cross aldol condensation

    OR

    (a) How would you account for the following:

    (i) Aldehydes are more reactive than ketones towards nucleophiles.

    (ii) The boiling points of aldehydes and ketones are lower than those of the corresponding acids.

    1. The aldehydes and ketones undergo a number of addition reactions.

    (b) Give chemical tests to distinguish between:

    (i) Acetaldehyde and benzaldehyde

    (ii) Propanone and propanol

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