Board Paper of Class 12-Science 2012 Chemistry (SET 3) - 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 2
What
is the role of graphite in the electrometallurgy of aluminium?
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- Question 6
Define
the term, ‘homopolymerisation’ giving an example.
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- Question 7
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 8
Arrange
the following compounds in an increasing order of their reactivity in
nucleophilic addition reactions: ethanol, propanal, propanone,
butanone.
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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
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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- Question 11
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 12
Explain
the following terms giving one example for each:
(i)
Miscelles
(ii)
Aerosol
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- Question 13
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 14
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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- Question 15
What
is meant by (i) peptide linkage (ii) biocatalysts?
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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
any two reactions of glucose which cannot be explained by the open
chain structure of glucose molecule.
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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
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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- 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
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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- Question 23
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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- 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
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 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
Explain
the following terms giving one example of each type:
(i)
Antacids,
(ii)
Disinfectants,
(iii)
Enzymes.
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- Question 28
(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 29
(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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- Question 30
(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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