12th Chemistry Paper Solutions Set 3 : CBSE Delhi Previous Year 2012

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.
Q1 :

What is meant by “doping”™ in a semiconductor?


Answer :

Doping is the process of increasing conductivity of the intrinsic semiconductors by adding suitable impurity.

Q2 :

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


Answer :

In the metallurgy of aluminium, steel cathode and graphite anode are used. The graphite anode is useful for the reduction of Al2O3 into Al.

Q3 :

Of PH3 and H2S which is more acidic and why?


Answer :

H2S is more acidic than PH3 because S is more electronegative than P. So, S-H bond is more polar than P-H bond resulting in easier removal of H+ ion.

Q4 :

Give the IUPAC name of the following compound.


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Q5 :

Draw the structure of hex-1-en-3-ol compound.


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Q6 :

Define the term, “homopolymerisation”™ giving an example.


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Q7 :

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

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


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Q8 :

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


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Q9 :

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 richloroacetic 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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Q10 :

Name the two groups into which phenomenon of catalysis can be divided. Give an example of each group with the chemical equation involved.


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Q11 :

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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Q12 :

Explain the following terms giving one example for each:

(i) Miscelles

(ii) Aerosol


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Q13 :

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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Q14 :

Describe the principle involved in each of the following processes.

(i) Mond process for refining of Nickel.

(ii) Column chromatography for purification of rare elements.


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Q15 :

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


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Q16 :

Complete the following chemical equations:

(i)

(ii)


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Q17 :

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

(i) Nylon 6

(ii) Polypropene


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Q18 :

Write any two reactions of glucose which cannot be explained by the open chain structure of glucose molecule.


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Q19 :

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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Q20 :

15.0 g of an unknown molecular material was dissolved in 450 g of water. The resulting solution was found to freeze at −0.34°C. What is the molar mass of this material? (Kf for water

= 1.86 K kg mol−1)3


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Q21 :

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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Q22 :

Explain the following observations giving as appropriate reason for each.

(i) The enthalpies of atomization of transition elements are quite high.

(ii) There occurs much more frequent metal-metal bonding in compounds of heavy transition metals (i.e 3rd series).

(iii) Mn2+ is much more resistant than Fe2+ towards oxidation.


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Q23 :

Write the name, the structure and the magnetic behaviour of each one of the following complexes:

(i) [Pt (NH3)Cl(NO2)]

(ii) [Co(NH3)4 Cl2]Cl

(iii) Ni(CO)4

(At.nos. Co = 27, Ni = 28, Pt = 78)


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Q24 :

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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Q25 :

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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Q26 :

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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Q27 :

Explain the following terms giving one example of each type:

(i) Antacids,

(ii) Disinfectants,

(iii) Enzymes.


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Q28 :

(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 x 10-3S cm-1?


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Q29 :

(a) Illustrate the following name reaction giving suitable example in each case:

(i) Clemmensen reduction

(ii) Hell-Volhard-Zelinsky reaction

(b) How are the following conversions carried out?

(i) Ethylcyanide to ethanoic acid

(ii) Butan-1-ol to butanoic acid

(iii) Benzoic acid to m-bromobenzoic acid

OR

(a) Illustrate the following reactions giving a suitable example for each.

(i) Cross aldol condensation

(ii) Decarboxylation

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

(i) Pentan-2-one and Pentan-3-one

(ii) Benzaldehyde and Acetophenone

(iii) Phenol and Benzoic acid


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Q30 :

(a) Draw the molecular structures of following compounds:

(i) XeF6

(ii) H2S2O8

(b) Explain the following observations:

(i) The molecules NH3 and NF3 have dipole moments which are of opposite direction.

(ii) All the bonds in PCl5 molecule are not equivalent.

(iii) Sulphur in vapour state exhibits paramagnetism.

OR

(a) Complete the following chemical equations:

(i) XeF4 + SbF5 →

(ii) Cl2 + F2 (excess) →

(b) Explain each of the following:

(i) Nitrogen is much less reactive than phosphorus.

(ii) The stability of +5 oxidation state decreases down group 15.

(iii) The bond angles (O - N - O) are not of the same value in


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