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Board Paper of Class 12-Science 2012 Chemistry Abroad(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

    How would you distinguish between a metallic solid and an ionic solid other than by metallic luster?

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  • Question 2

    What is meant by ‘shape selective catalysis’?

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  • Question 3

    Write the reaction involved in the extraction of silver after the silver ore has been leached with

    NaCN.

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  • Question 4

    Which is more acidic and why H2O or H2S?

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  • Question 5

    Of the two alcohols;

    (a) CH2 = CH − CH2 OH and

    (b) CH2 = CH − CH2 − CH2 OH, which one will react more easily with conc. HCI in the presence of ZnCl2?

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  • Question 6

    Draw the molecular structure of the compound 4-methyplent-3-en-2-one.

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  • Question 7

    What is meant by ‘narrow spectrum antibiotics’?

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  • Question 8

    Of the two bases named below, which one is present is RNA and which one is present in DNA?

    (i) Thymine

    (ii) Uracil

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  • Question 9

    Define the following terms:

    (a) Order of a reaction

    (b) Activation energy of a reaction

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  • Question 10

    (a) Define any two of the following terms:

    (i) van’t Hoff factor

    (ii) Mole fraction

    (iii) Ebullioscopic constant

    (b) State Raoult’s law

    OR

    The density of water of a lake is 1.25 g(mL)−1 and one kg of this water contains 92 g of Na+ ions. What is the molarity of Na+ ions in the water of the lake? (Atomic mass of Na = 23.00 u)

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  • Question 11

    Explain the following:

    (i) The chemical reactivity of nitrogen is much less than that of phosphorus.

    (ii) SF6 is kinetically inert.

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  • Question 12

    Name one chief ore each of copper and aluminium. Name the method used for the concentration of these two ores.

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  • Question 13

    Draw the molecular structures of the following species:

    (i) H2S2O8

    (ii) XeF2

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  • Question 14

    Explain as to why

    (i) Alkyl halides, though polar, are immiscible with water.

    (ii) Grignard’s reagents should be prepared under anhydrous conditions.

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  • Question 15

    What are ambident nucleophiles? Explain giving an example.

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  • Question 16

    Complete the following reaction equations:

    (i) C6H5N2Cl + H3PO2 + H2O →

    (ii) C6H5NH2 + Br2(aq.) →

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  • Question 17

    Describe the following giving the chemical equation in each case:

    (i) Carbylamine reaction

    (ii) Hofmann’s bromamide reaction

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  • Question 18

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

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  • Question 19

    At 25° C the saturated vapour pressure of water is 3.165 kPa (23.75 mm Hg). Find the saturated vapour pressure of a 5% aqueous solution of urea (carbamide) at the same temperature. (Molar mass of urea = 60.05 g mol−1)

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  • Question 20

    Iron has a body centered cubic closed unit cell with the cell dimension of 286.65 pm. Density of iron is 7.874 g cm−3. Use this information to calculate Avogadro’s number.

    (Atomic mass of Fe = 55.845 u).

    OR

    Silver cryatallises in face centered cubic (fcc) unit cell. If the radius of silver atom is 145 pm, what is the length of each side of the unit cell?

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  • Question 21

    Consider the reaction.

    2A + B → C + D

    Following result were obtained in experiments designed to study the rate of reaction:

    Exp No.

    Initial concentration

    (mol L−1)

    Initial rate of

    formation

    [A]

    [B]

    [D] (M/min)

    1

    0.10

    0.10

    1.5 × 10−3

    2

    0.20

    0.20

    3.0 × 10−3

    3

    0.20

    0.40

    6.0 × 10−3

    (a) Write the rate law for the reaction.

    (b) Calculate the value of rate constant for the reaction.

    (c) Which of the following possible reaction mechanisms is constant with the rate law found in (a)?

    I. A + B → C + E (slow)

    A + E → D (fast)

    II. B → C + E(slow)

    A + E → F (fast)

    A + F → D (fast)

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  • Question 22

    Differentiate among a homogeneous solution, a suspension and a colloidal solution, given a suitable example of each

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  • Question 23

    Complete the following chemical equations:

    (i) HgCl2 + PH3

    (ii)

    (iii)

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  • Question 24

    Name the following complexes and draw the structure of one possible isomer of each:

    (i) [Cr(C2O4)3]3−

    (ii) [Pt(NH3)2 Cl2]

    (iii) [Co(en)2Cl2]+

    (en = ethane-1, 2-diamine or ethylenediamine)

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  • Question 25

    State the products of the following reactions:

    (i) CH3 − CH2 − CH2 − O − CH3 + HBr →

    (ii)

    (iii)

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  • Question 26

    Explain the meaning of the following terms:

    (i) Invert sugar

    (ii) Polypeptide

    (iii) Enzymes

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  • Question 27

    Write the structure of the monomer of each of the following polymers:

    (i) Nylon-6

    (ii) Teflon

    (iii) Neoprene

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  • Question 28

    (a) Complete and balance the following chemical equations.

    (i)

    (ii)

    (b) Explain the following observation:

    (i) Transition elements and their compounds are known to act as catalysts.

    (ii)The higher oxidation states are usually exhibited by the members in the middle of a series of transition elements.

    (iii) The metal-metal bonding is more frequently found with the second and third series of transition elements.

    OR

    (a) Calculate the number of unpaired electrons in the following gaseous state ions:

    Mn3+, Cr3+, V3+ and Fe2+

    Which one of these is the most stable in aqueous solutions?

    (At nos, V = 23, Cr = 24, Mn = 25, Fe = 26)

    (b) Explain the following observation:

    (i) The transition metal ions are usually colored in aqueous solutions.

    (ii) Cu (I) is not stable in an aqueous solution.

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

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  • Question 29

    (a) What type of battery is the lead storage battery? Write the anode and cathode reactions and the overall reaction occurring in a lead storage battery sending out an electric current.

    (b) A voltaic cell is set up at 25°C with the half-cells

    Ag+ (0.001 M) |Ag and Cu2+ (0.10 M)| Cu.

    What should be its cell potential? (E° = 0.46 V; Log105 = 5)

    OR

    (a)Define the term molar conductivity and explain how molar conductivity changes with solution concentration for weak and strong electrolytes.

    (b)A strip of nickel metal is placed in a 1-molar solution of Ni(NO3)2 and a strip of silver metal is placed in a 1-molar solution of AgNO3. An electrochemical cell is created when the two solutions are connected by a salt bridge and the two strips are connected by wires to a voltameter.

    (i) Write the balanced equations for the overall reactions occurring in the cell and calculate the cell potential.

    (ii) Calculate the cell potential, E, at 25° C for the cell if the initial concentration of Ni(NO3)2 is 0.100 molar and the initial concentration of AgNO3 is 1.00 molar.

    [ENi2+, Ni = − 0.25 V; E+Ag+/Ag = 0.80 V; Log 10−1 = − 1]

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  • Question 30

    (a) Describe the mechanism of the addition of Grignard reagent to the carbonyl group of a compound a form an adduct which on hydrolysis yield an alcohol.

    (b) Draw the structure of the following compounds:

    (i) 3-Methylbutanal

    (ii) Hexane-1, 6-dioic acid

    (iii) p-Nitropropiophenone

    OR

    (a) Illustrate the following reactions giving suitable chemical equations for each:

    (i) Cannizzaro reaction

    (ii) Hell-Volhard-Zelinsky reaction.

    (b) How would you bring about the following conversions? Write the complete equations in each case:

    (i) Ethanal to 3-hydroxybutanal

    (ii) Benzoic acid to m-nitrobenzyl alcohol

    (iii) Benzaldehyde to benzophenone

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