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Board Paper of Class 12-Science 2011 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

    ‘Crystalline solids are anisotropic in nature’. What does this statement mean?

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  • Question 2

    Express the relation between conductivity and molar conductivity of a solution held in a cell.

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  • Question 4

    Draw the structure of XeF2 molecule. 

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  • Question 5

    Write the IUPAC name of the following compound: 

    (CH3)3 CCH2Br

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  • Question 6

    Draw the structure of 3-methylbutanal.

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  • Question 7

    Arrange the following compounds in an increasing order of their solubility in water: 

    C6H5NH2, (C2H5)2NH, C2H5NH2

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  • Question 9

    The chemistry of corrosion of iron is essentially an electrochemical phenomenon. Explain the reactions occurring during the corrosion of iron in the atmosphere.

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  • Question 10

    Determine the values of equilibrium constant (KC) and ΔG° for the following reaction: 

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  • Question 11

    Distinguish between ‘rate expression’ and ‘rate constant’ of a reaction.

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  • Question 12

    State reasons for each of the following: 

    (i) The N − O bond in is shorter than the N − O bond in

    (ii) SF6 is kinetically an inert substance. 

    OR

    State reasons for each of the following: 

    (i) All the P-Cl bonds in PCl5 molecule are not equivalent. 

    (ii) Sulphur has greater tendency for catenation than oxygen.

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  • Question 13

    Assign reasons for the following: 

    (i) Copper (I) ion is not known in aqueous solution. 

    (ii) Actinoids exhibit greater range of oxidation states than Lanthanoids. 

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  • Question 14

    Explain the following giving one example for each: 

    (i) Reimer-Tiemann reaction. 

    (ii) Friedel Craft’s acetylation of anisole.

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  • Question 15

    How would you obtain 

    (i) Picric acid (2, 4, 6-trinitrophenol) from phenol, 

    (ii) 2-Methylpropene from 2-methylpropanol? 

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  • Question 16

    What is essentially the difference between α-form of glucose and β-form of glucose? Explain.

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  • Question 17

    Describe what you understand by primary structure and secondary structure of proteins.

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  • Question 18

    Mention two important uses of each of the following:

    (i) Bakelite

    (ii) Nylon 6

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  • Question 19

    Silver crystallizes in face-centred cubic unit cell. Each side of this unit cell has a length of 400 pm. Calculate the radius of the silver atom. (Assume the atoms just touch each other on the diagonal across the face of the unit cell. That is each face atom is touching the four corner atoms.) 

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  • Question 20

    Nitrogen pentoxide decomposes according to equation: 2N2O5(g) → 4NO2(g) + O2(g) 

    This first order reaction was allowed to proceed at 40° C and the data below were collected:

    [N2O5] (M) Time (min)
    0.400 0.00
    0.289 20.0
    0.209 40.0
    0.151 60.0
    0.109 80.0

    (a) Calculate the rate constant. Include units with your answer. 

    (b) What will be the concentration of N2O5 after 100 minutes? 

    (c) Calculate the initial rate of reaction.

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  • Question 21

    Explain how the phenomenon of adsorption finds application in each of the following processes:

    (i) Production of vacuum

    (ii) Heterogeneous catalysis

    (iii) Froth Floatation process

    OR

    Define each of the following terms:

    (i) Micelles

    (ii) Peptization

    (iii) Desorption

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  • Question 22

    Describe the principle behind each of the following processes:

    (i) Vapour phase refining of a metal.

    (ii) Electrolytic refining of a metal.

    (iii) Recovery of silver after silver ore was leached with NaCN.

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  • Question 23

    Complete the following chemical equations:

    (i)

    (ii)

    (iii)

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  • Question 24

    Write the name, stereochemistry and magnetic behaviour of the following: 

    (At. nos. Mn = 25, Co = 27, Ni = 28) 

    (i) K4[Mn(CN)6

    (ii) [Co(NH3)5Cl]Cl2

    (iii) K2[Ni(CN)4]

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  • Question 25

    Answer the following: 

    (i) Haloalkanes easily dissolve in organic solvents, why? 

    (ii) What is known as a racemic mixture? Give an example. 

    (iii) Of the two bromoderivatives, C6H5CH(CH3)Br and C6H5CH(C6H5)Br, which one is more reactive in substitution reaction and why? 

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  • Question 26

    (a) Explain why an alkyl-amine is more basic than ammonia. 

    (b) How would you convert 

    (i) Aniline to nitrobenzene 

    (ii) Aniline to iodobenzene?

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  • Question 27

    Describe the following giving one example for each: 

    (i) Detergents 

    (ii) Food preservatives 

    (iii) Antacids 

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  • Question 28

    (a) Differentiate between molarity and molality for a solution. How does a change in temperature influence their values? 

    (b) Calculate the freezing point of an aqueous solution containing 10.50 g of MgBr2 in 200 g of water. (Molar mass of MgBr2 = 184 g) (Kf for water = 1.86 K kg mol−1

    OR

    (a) Define the terms osmosis and osmotic pressure. Is the osmotic pressure of a solution a colligative property? Explain. 

    (b) Calculate the boiling point of a solution prepared by adding 15.00 g of NaCl to 250.0 g of water. (Kb for water = 0.512 K kg mol−1), (Molar mass of NaCl = 58.44 g)

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  • Question 29

    (a) Give chemical tests to distinguish between 

    (i) Propanal and propanone, 

    (ii) Benzaldehyde and acetophenone. 

    (b) How would you obtain 

    (i) But-2-enal from ethanal, 

    (ii) Butanoic acid from butanol, 

    (iii) Benzoic acid from ethylbenzene? 

    OR

    (a) Describe the following giving linked chemical equations: 

    (i) Cannizzaro reaction 

    (ii) Decarboxylation 

    (b) Complete the following chemical equations: 

    (i) 

    (ii) 

    (iii)

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  • Question 30

    (a) Explain the following: 

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

    (ii) F2 is most reactive of all the four common halogens. 

    (b) Complete the following chemical equations: 

    (i) C + H2SO4 (conc) →

    (ii) P4 + NaOH + H2O →

    (iii)

    OR

    (a) Account for the following: 

    (i) The acidic strength decreases in the order HCl > H2S > PH3

    (ii) Tendency to form pentahalides decreases down the group in group 15 of the periodic table. 

    (b) Complete the following chemical equations: 

    (i) P4 + SO2Cl2

    (ii) XeF2 + H2O →

    (iii)

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