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Board Paper of Class 12-Science 2013 Chemistry (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

    How many atoms constitute one unit cell of a face-centered cubic crystal? (1)

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  • Question 2

    Name the method used for the refining of Nickel metal. (1)

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  • Question 3

    What is the covalency of nitrogen in N2O5? (1)

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  • Question 5

    What happens when CH3 − Br is treated with KCN? (1)

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  • Question 6

    Write the structure of 3-methyl butanal. (1)

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  • Question 7

    Arrange the following in increasing order of their basic strength in aqueous solution: (1)

    CH3.NH2, (CH3)3N, (CH3)2NH

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  • Question 8

    What are three types of RNA molecules which perform different functions? (1)

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  • Question 9

    18 g of glucose, C6H12O6 (Molar Mass = 180 g mol−1) is dissolved in 1 kg of water in a sauce pan. At what temperature will this solution boil? (2)

    (Kb for water = 0.52 K kg mol−1, boiling point of pure water = 373.15 K)

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  • Question 10

    The conductivity of 0.20 M solution of KCl at 298 K is 0.025 S cm−1. Calculate its molar conductivity. (2)

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  • Question 11

    Write the dispersed phase and dispersion medium of the following colloidal systems: (2)

    (i) Smoke

    (ii) Milk

    OR

    What are lyophilic and lyophobic colloids ? Which of these sols can be easily coagulated on the addition of small amounts of electrolytes?

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  • Question 12

    Write the differences between physisorption and chemisorption with respect to the following: (2)

    (i) Specificity

    (ii) Temperature dependence

    (iii) Reversibility and

    (iv) Enthalpy change

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  • Question 13

    (a) Which solution is used for the leaching of silver metal in the presence of air in the metallurgy of silver? (2)

    (b) Out of C and CO, which is a better reducing agent at the lower temperature range in the blast furnace to extract iron from the oxide ore?

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  • Question 14

    What happens when (2)

    (i) PCl5 is heated ?

    (ii) H3PO3 is heated ?

    Write the reactions involved.

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  • Question 15

    (a) Which metal in the first transition series (3d series) exhibits + 1 oxidation state most frequently and why? (2)

    (b) Which of the following cations are coloured in aqueous solutions and why ?

    Sc3+, V3+, Ti4+, Mn2+ (At. Nos. Sc = 21, V = 23, Ti = 22, Mn = 25)

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  • Question 16

    Chlorobenzene is extremely less reactive towards a nucleophilic substitution reaction. Give two reasons for the same. (2)

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  • Question 17

    Explain the mechanism of the following reaction: (2)

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  • Question 18

    How will you convert: (2)

    (i) Propene to Propan-2-ol?

    (ii) Phenol to 2, 4, 6 − trinitrophenol?

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  • Question 19

    (a) What type of semiconductor is obtained when silicon is doped with boron? (3)

    (b) What type of magnetism is shown in the following alignment of magnetic moments?

    (c) What type of point defect is produced when AgCl is doped with CdCl2?

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  • Question 20

    Determine the osmotic pressure of a solution prepared by dissolving 2.5 × 10−2 g of K2SO4 in 2L of water at 25°C, assuming that it is completely dissociated. (3)

    (R = 0.0821 L atm K−1 mol−1, Molar mass of K2SO4 = 174 g mol−1)

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  • Question 21

    Calculate the emf of the following cell at 298 K: (3)

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  • Question 22

    How would you account for the following? (3)

    (i) Transition metals exhibit variable oxidation states.

    (ii) Zr (Z = 40) and Hf (Z = 72) have almost identical radii.

    (iii) Transition metals and their compounds act as catalyst.

    OR

    Complete the following chemical equations:

    (i)

    (ii)

    (iii)

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  • Question 23

    Write the IUPAC names of the following coordination compounds: (3)

    (i) [Cr(NH3)3Cl3]

    (ii) K3[Fe(CN)6]

    (iii) [CoBr2(en)2]+, (en = ethylenediamine)

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  • Question 24

    Give the structures of A, B and C in the following reactions: (3)

    (i)

    (ii)

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  • Question 25

    Write the names and structure of the monomers of the following polymers: (3)

    (i) Buna − S

    (ii) Neoprene

    (iii) Nylon-6, 6

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  • Question 26

    After watching a programme on TV about the adverse effects of junk food and soft drinks on the health of school children, Sonali, a student of Class XII, discussed the issue with the school principal. Principal immediately instructed the canteen contractor to replace the fast food with the fibre and vitamins rich food like sprouts, salad, fruits etc. This decision was welcomed by the parents and the students. (3)

    After reading the above passage, answer the following questions:

    (a) What value are expressed by Sonali and the Principal of the school?

    (b) Give two examples of water-soluble vitamins.

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  • Question 27

    (a) Which one of the following is a food preservative? (3)

    Equanil, Morphine, Sodium benzoate

    (b) Why is bithional added to soap?

    (c) Which class of drugs is used in sleeping pills?

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  • Question 28

    (a) A reaction is second order in A and first order in B.

    (i) Write the differential rate equation.

    (ii) How is the rate affected on increasing the concentration of A three times?

    (iii) How is the rate affected when the concentrations of both A and B are doubled?

    (b) A first order reaction takes 40 minutes for 30% decomposition. Calculate t1/2 for this reaction. (Given log 1.428 = 0.1548) (5)

    OR

    (a) For a first order reaction, show that time required for 99% completion is twice the time required for the completion of 90% of reaction.

    (b) Rate constant ‘k’ of a reaction varies with temperature ‘T’ according to the equation:

    Where Ea is the activation energy. When a graph is plotted for a straight line with a slope of −4250 K is obtained. Calculate ‘Ea’ for the reaction.

    (R = 8.314 JK−1 mol−1)

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  • Question 29

    (a) Give reasons for the following:

    (i) Bond enthalpy of F2 is lower than that of Cl2.

    (ii) PH3 has lower boiling point than NH3.

    (b) Draw the structures of the following molecules:

    (i) BrF3

    (ii) (HPO3)3

    (iii) XeF4 (5)

    OR

    (a) Account for the following:

    (i) Helium is used in diving apparatus.

    (ii) Fluorine does not exhibit positive oxidation state.

    (iii) Oxygen shows catenation behavior less than sulphur.

    (b) Draw the structures of the following molecules:

    (i) XeF2

    (ii) H2S2O8

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  • Question 30

    (a) Although phenoxide ion has more number of resonating structures than Carboxylate ion, Carboxylic acid is a stronger acid than phenol. Give two reasons.

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

    (i) Propanone to propane

    (ii) Benzoyl chloride to benzaldehyde

    (iii) Ethanal to but-2-enal (5)

    OR

    (a) Complete the following reactions:

    (i)

    (ii)

    (iii)

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

    (i) Ethanal and Propanal

    (ii) Benzoic acid and Phenol

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