Board Paper of Class 12-Science 2008 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
What is the coordination number of each type of ions in a
rock-salt type crystal structure?
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- Question 2
Define the term ‘order of reaction’ for chemical
reactions.
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- Question 3
What causes Brownian movement in a colloidal solution?
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- Question 4
In which one of the two structures, and , the bond angle has a higher
value?
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- Question 6
Arrange the following compounds in an increasing order of their
acid strengths:
(CH3)2CHCOOH,
CH3CH2CH(Br)COOH,
CH3CH(Br)CH2COOH
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- Question 7
Write
a chemical reaction in which the iodide ion replaces the diazonium
group in a diazonium salt.
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- Question 8
Name a substance that can be used as an
antiseptic as well as a disinfectant.
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- Question 9
Explain as to why haloarenes are much less reactive than
haloalkanes towards nucleophilic substitution reactions.
OR
Which
compound in each of the following pairs will react faster in SN2
reaction with −OH? Why?
(i) CH3Br
or CH3I
(ii) (CH3)3CCl
or CH3Cl
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- Question 10
(a) State the IUPAC name of the following compound:
(b) Complete the following chemical equation:
CH3CH2CH=CH2
+ HBr
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- Question 11
State Henry’s law correlating the pressure of a gas and its
solubility in a solvent and mention two applications for the law.
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- Question 12
A
first order decomposition reaction takes 40 minutes for 30%
decomposition. Calculate its
value.
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- Question 13
What
is meant by the ‘rate constant, k’
of a reaction? If the concentration be expressed in mol L−1
units and time in seconds, what would be the units for k
(i) for a zero-order reaction
and (ii) for a first-order reaction?
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- Question 14
Define the following terms in relation to proteins:
(i) Peptide linkage
(ii) Denaturation
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- Question 15
List
the reactions of glucose which cannot
be explained by its open-chain structure.
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- Question 16
Assign a reason for each of the following statements:
(i) Ammonia is a stronger base than phosphine.
(ii) Sulphur in vapour state exhibits a paramagnetic behaviour.
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- Question 17
Draw the structure of the following molecules:
(i) SF4
(ii) XeF4
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- Question 18
What are biodegradable and non-biodegradable detergents? Give one example of each class.
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- Question 19
What is semiconductor? Describe the two main types of
semiconductors and explain mechanisms for their conduction.
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- Question 20
Calculate
the temperature at which a solution containing 54
g of glucose, (C6H12O6),
in 250 g of water will freeze.
(Kf
for water = 1.86 K mol−1
kg)
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- Question 21
What
are lyophilic and lyophobic sols? Give one example of each type.
Which one of these two types of sols
is easily coagulated and why?
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- Question 22
State briefly the principles which serve as basis for the
following operations in metallurgy:
(i) Froth floatation process
(ii) Zone refining
(iii) Refining by liquation
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- Question 23
Write chemical equations for the following processes:
(i) Chlorine reacts with a hot concentrated solution of sodium
hydroxide
(ii) Orthophosphorous acid is heated
(iii) PtF6
and xenon are mixed together
OR
Complete the following chemical equations:
(i) Ca3P2(s)
+ H2O(l)
→……..
(iii) F2(g)
+ H2O(l)
→……..
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- Question 24
(a) What is a ligand? Give an example of a bidentate ligand.
(b) Explain as to how the two complexes of
nickel, [Ni(CN)4]2−
and Ni(CO)4,
have different structures but do not differ in their magnetic
behaviour. (Ni = 28)
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- Question 25
Name the reagents which are used in the following conversions:
(i) A primary alcohol to an aldehyde
(ii) Butan-2-one to butan-2-ol
(iii) Phenol to 2, 4, 6-tribromophenol
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- Question 26
Account for the following observations:
(i) pKb
for aniline is more than that for methylamine.
(ii) Methylamine solution in water reacts with ferric chloride
solution to give a precipitate of ferric hydroxide.
(iii) Aniline does not undergo Friedel-Crafts reaction.
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- Question 27
Write the names and structures of the monomers
of the following polymers:
(i) Buna-S
(ii) Neoprene
(iii) Nylon-6
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- Question 28
Conductivity
of 0.00241 M acetic acid solution is
7.896 × 10−5
S cm−1.
Calculate its molar conductivity in this solution. If
for
acetic acid be 390.5 S cm2
mol−1,
what would be its dissociation constant?
OR
Three
electrolytic cells A, B and C containing solutions of zinc sulphate,
silver nitrate and copper sulphate
respectively, are connected in series. A steady current of 1.5 ampere
was passed through them until 1.45 g of silver was deposited at the
cathode of cell B. How long did the current flow? What mass of copper
and what mass of zinc were deposited in the concerned cells?
(Atomic masses of Ag = 108, Zn = 65.4, Cu = 63.5)
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- Question 29
Assign reasons for the following:
(i) The enthalpies of atomisation of transition elements are high.
(ii) The transition metals and many of their compounds act as good
catalyst.
(iii) From element to element the actinoid contraction is greater
than the lanthanoid contraction.
(iv) The E0
value for the Mn3+/Mn2+
couple is much more positive than that for Cr3+/Cr2+.
(v) Scandium (Z = 21) does not exhibit variable oxidation states
and yet it is regarded as a transition element.
OR
(a) What may be the possible oxidation states
of the transition metals with the following d
electronic configurations in the ground state of their atoms:
3d34s2,
3d54s2
and 3d64s2
Indicate relative stability of oxidation states
in each case.
(b) Write steps involved in the preparation of
(i) Na2CrO4
from chromite ore and (ii) K2MnO4
from pyrolusite ore.
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- Question 30
(a) Complete the following reaction statements
by giving the missing starting material, reagent or product as
required:
(i)
(ii)
(iii)
(b) Describe the following reactions:
(i) Cannizaro reaction
(ii) Cross aldol condensation
OR
(a) How would you account for the following:
(i) Aldehydes are more reactive than ketones towards nucleophiles.
(ii) The boiling points of aldehydes and
ketones are lower than those of the corresponding acids.
The aldehydes and ketones undergo a number of addition reactions.
(b) Give chemical tests to distinguish between:
(i) Acetaldehyde and benzaldehyde
(ii) Propanone and propanol
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