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Board Paper of Class 12-Science 2012 Chemistry Delhi(SET 2) - 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

    Write a point of distinction between a metallic solid and an ionic solid other than metallic lustre.

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  • Question 2

    Which one of is not likely to exist and why?

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  • Question 3

    What is the role of graphite in the electrometallurgy of aluminium?

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  • Question 4

    Arrange the following compounds in an increasing order of their reactivity in nucleophilic addition reactions: ethanol, propanal, propanone, butanone.

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  • Question 5

    Draw the structural formula of 2-methylpropan-2-ol molecule.

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  • Question 6

    Give the IUPAC name of the following compound.

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  • Question 7

    Define the term, ‘homopolymerisation’ giving an example.

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  • Question 8

    Arrange the following in the decreasing order of their basic strength in aqueous solutions:

    CH3NH2, (CH3)2NH, (CH3)3 N and NH3

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  • Question 9

    A 1.00 molal aqueous solution of trichloroacetic acid (CCl3COOH) is heated to its boiling point. The solution has the boiling point of 100.18°C. Determine the van’t Hoff factor for trichloroacetic acid. (Kb for water = 0.512 kg mol−1)

    OR

    Define the following terms:

    (i) Mole fraction

    (ii) Isotonic solutions

    (iii) Van’t Hoff factor

    (iv) Ideal solution

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  • Question 10

    What do you understand by the ‘order of a reaction’? Identify the reaction order from each of the following units of reaction rate constant:

    (i) L−1 mol s−1

    (ii) L mol−1 s−1

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  • Question 11

    Describe a conspicuous change observed when

    (i) a solution of NaCl is added to a sol of hydrated ferric oxide.

    (ii) a beam of light is passed through a solution of NaCl and then through a sol.

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  • Question 12

    What is meant by coagulation of a colloidal solution? Describe briefly any three methods by which coagulation of lyophobic sols can be carried out.

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  • Question 13

    Describe the following:

    (i) The role of cryolite in electro metallurgy of aluminium.

    (ii) The role of carbon monoxide in the refining of crude nickel.

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  • Question 14

    What is meant by (i) peptide linkage (ii) biocatalysts?

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  • Question 15

    Explain the following giving an appropriate reason in each case.

    (i) O2 and F2 both stabilize higher oxidation states of metals but O2 exceeds F2 in doing so.

    (ii) Structures of Xenon fluorides cannot be explained by Valence Bond approach.

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  • Question 16

    Complete the following chemical equations:

    (i)

    (ii)

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  • Question 17

    Draw the structure of the monomer for each of the following polymers:

    (i) Nylon 6

    (ii) Polypropene

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  • Question 18

    Write the main structural difference between DNA and RNA. Of the two bases, thymine and uracil, which one is present in DNA?

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  • Question 19

    Tungsten crystallizes in body centred cubic unit cell. If the edge of the unit cell is 316.5 pm, what is the radius of tungsten atom?

    OR

    Iron has a body centred cubic unit cell with a cell dimension of 286.65 pm. The density of iron is 7.874 g cm−3. Use this information to calculate Avogadro’s number (At. Mass of Fe = 55.845 u)

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  • Question 20

    A solution of glycerol (C3H8O3) in water was prepared by dissolving some glycerol in 500 g of water. This solution has a boiling point of 100.42°C while pure water boils at 100°C. What mass of glycerol was dissolved to make the solution?

    (Kb = for water = 0.512 K kg mol−1)

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  • Question 21

    For the reaction

    2NO(g) + Cl2(g) → 2 NOCl(g)

    The following data were collected. All the measurements were taken at 263 K:

    Experiment No.

    Initial [NO] (M)

    Initial [Cl2] (M)

    Initial rate of disappearance of Cl2 (M/min)

    1

    0.15

    0.15

    0.60

    2

    0.15

    0.30

    1.20

    3

    0.30

    0.15

    2.40

    4

    0.25

    0.25

    ?

    (a) Write the expression for rate law.

    (b) Calculate the value of rate constant and specify its units.

    (c) What is the initial rate of disappearance of Cl2 in exp. 4?

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  • Question 22

    State a reason for each of the following situations:

    (i) Co2+ is easily oxidized to Co3+ in presence of a strong ligand.

    (ii) Co is a stronger complexing reagent than NH3.

    (iii) The molecular shape of Ni(CO)4 is not the same as that of [Ni(CN)4]2−

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  • Question 23

    How would you account for the following?

    (i) With the same d-orbital configuration (d4) Cr2+ is a reducing agent while Mn3+ is an oxidizing agent.

    (ii) The actinoids exhibit a larger number of oxidation states than the corresponding members in the lanthanoid series.

    (iii) Most of the transition metal ions exhibit characteristic in colours in aqueous solutions.

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  • Question 24

    Write chemical equation for the following conversions:

    (i) Nitrobenzene to benzoic acid.

    (ii) Benzyl chloride to 2-phenylethanamine.

    (iii) Aniline to benzyl alcohol.

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  • Question 25

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

    (i) Tranquilizers

    (ii) Food preservatives

    (iii) Synthetic detergents

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  • Question 26

    Draw the structure and name the product formed if the following alcohols are oxidized. Assume that an excess of oxidizing agent is used.

    (i) CH3CH2CH2CH2OH

    (ii) 2-butenol

    (iii) 2-methyl-1-proponal

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  • Question 27

    Although chlorine is an electron withdrawing group, yet it is ortho-, para-directing in electrophilic aromatic substitution reactions. Explain why it is so?

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  • Question 28

    (a) Complete the following chemical reactions equations:

    (i)

    (ii)

    (b) Predict the shape and the asked angle (90° or more or less) in each of the following cases:

    (i) and the angle O − S − O

    (ii) ClF3 and the angle F − Cl − F

    (iii) XeF2 and the angle F − Xe − F

    OR

    (a) Complete the following chemical equations:

    (i)

    (ii)

    (b) Draw the structures of the following molecules:

    (i) H3PO2

    (ii) H2S2O7

    (iii) XeOF4

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  • Question 29

    (a) What type of a battery is the lead storage battery? Write the anode and the cathode reactions and the overall reaction occurring in a lead storage battery when current is drawn from it.

    (b) In the button cell, widely used in watches, the following reaction takes place

    Determine E° and ΔG° for the reaction

    OR

    (a) Define molar conductivity of a solution and explain how molar conductivity changes with change in concentration of solution for a weak and a strong electrolyte.

    (b) The resistance of a conductivity cell containing 0.001 M KCl solution at 298 K is 1500Ω. What is the cell constant if the conductivity of 0.001 M KCl solution at 298 K is 0.146 × 10−3 S cm−1?

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  • Question 30

    (a) Give a plausible explanation for each one of the following:

    (i) There are − NH2 groups in semicarbazide. However, only one such group is involved in the formation of semicarbazones.

    (ii) Cyclohexanone forms cyanohydrins in good yield but 2, 4, 6-trimethylcyclohexanone does not.

    (b) An organic compound with molecular formula C9H10O forms 2, 4, - DNP derivative, reduces Tollens’ reagent and undergoes Cannizzaro’s reaction. On vigorous oxidation it gives 1, 2-benzene-di-carboxylic acid. Identify the compound.

    OR

    (a) Give chemical tests to distinguish between

    (i) Phenol and Benzoic acid

    (ii) Benzophenone and Acetophenone

    (b) Write the structures of the main products of following reactions:

    (i)

    (ii)

    (iii)

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