Board Paper of Class 12-Science 2009 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
Which
point defect in crystals does not affect
the density of the relevant solid?
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- Question 3
Why
is the froth
flotation method selected for the concentration of sulphide ores?
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- Question 9
A
reaction is of second order with respect to a reactant. How will the
rate of reaction be affected if the concentration of this reactant is
(i)
Doubled,
(ii)
Reduced to half?
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- Question 10
Explain
the role of
(i)
Cryolite in the electrolytic reduction of alumina.
(ii)
Carbon monoxide in the purification of nickel.
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- Question 11
Draw
the structures of the following molecules:
(i)
XeF4
(ii)
BrF3
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- Question 12
Complete
the following chemical reaction equations:
(i)
(ii)
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- Question 13
Differentiate
between molality and molarity of a solution. What is the effect of
change in temperature of a solution on its molality and molarity?
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- Question 14
Which
ones in the following pairs of substances undergoes SN2
substitution reaction faster and why?
(i)
(ii)
or
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- Question 15
Complete the following reaction
equations:
(i)
(ii)
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- Question 16
Explain what is meant by
(i)
A peptide linkage
(ii)
A glycosidic linkage
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- Question 17
Name two water soluble vitamins, their sources and the diseases caused due to their deficiency in diet.
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- Question 18
Draw the structures of the
monomers of the following polymers:
(i)
Teflon
(ii)
Polythene
OR
What
is the repeating unit in the condensation polymer obtained by
combining HO2CCH2CH2CO2H
(succinic acid) and H2NCH2CH2NH2
(ethylene diamine)?
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- Question 19
Iron
has a body-centred
cubic unit cell with a cell edge of 286.65 pm. The density of iron is
7.87 g cm−3.
Use this information to calculate Avogadro’s number.
(At.
Mass of Fe = 56 g mol−1)
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- Question 20
100
mg of a protein is dissolved in just enough water to make 10.0 mL of
solution. If this solution has an osmotic pressure of 13.3 mm Hg at
25°C,
what is the molar mass of the protein?
(R
= 0.0821 L atm mol−1
K−1
and 760 mm Hg = 1 atm)
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- Question 21
A
first-order
reaction has a rate constant of 0.0051 min−1.
If we begin with 0.10 M concentration of the reactant, what
concentration of reactant will remain in the solution after 3 hours?
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- Question 22
How
are the following colloids different from each other with
respect to dispersion medium and dispersed phase? Give one example of
each type.
(i)
An aerosol (ii) A hydrosol (iii) An emulsion
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- Question 23
Account for the following:
(i)
NH3
is a stronger base than PH3.
(ii)
Sulphur has a greater tendency
for catenation than oxygen.
(iii)
Bond dissociation energy of F2
is
less than that of Cl2.
OR
Explain
the following situations:
(i) In the
structure of HNO3
molecule, the N − O bond (121 pm) is shorter than the N −
OH bond (140 pm).
(ii)
SF4
is easily hydrolysed whereas SF6
is
not easily hydrolysed.
(iii)
XeF2
has a straight linear structure and not a bent angular structure.
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- Question 24
For
the complex [Fe(en)2Cl2]
Cl, (en = ethylene diamine), identify
(i)
The oxidation number of iron,
(ii)
The hybrid orbitals and the shape of the complex,
(iii)
The magnetic behaviour of the complex,
(iv)
The number of geometrical isomers,
(v)
Whether there is an optical isomer also, and
(vi)
Name of the complex. (At. No. of Fe = 26)
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- Question 25
Explain the mechanism of the
following reactions:
(i) Addition of Grignard’s
reagent to the carbonyl group of a compound forming an adduct
followed by hydrolysis.
(ii)
Acid catalysed dehydration of an alcohol forming an alkene.
(iii)
Acid catalysed hydration of an alkene forming an alcohol.
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- Question 26
Giving an
example for each,
describe the following reactions:
(i)
Hofmann’s bromamide reaction
(ii)
Gatterman reaction
(iii)
A coupling reaction
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- Question 27
Explain
the following types of substances with one suitable example, for each
case:
(i) Cationic detergents
(ii) Food preservatives
(iii) Analgesics
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- Question 28
(a) Define
molar conductivity of a substance and describe how for weak and
strong electrolytes, molar conductivity changes with concentration of
solute. How is such change explained?
(b) A voltaic
cell is set up at 25°C
with the following half cells:
Ag+
(0.001 M) | Ag and Cu2+
(0.10 M) | Cu
What would be the voltage of this
cell?
()
OR
(a) State the
relationship amongst the cell constant of a cell, the resistance of
the solution in the cell and the conductivity of the solution. How is
molar conductivity of a solute related to the conductivity of its
solution?
(b) A voltaic
cell is set up at 25°C
with the following half-cells:
Al
| Al3+
(0.001 M) and Ni | Ni2+
(0.50
M)
Calculate the
cell voltage.
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- Question 29
(a)
Complete the following chemical reaction equations:
(i)
(ii)
(b) Explain the following
observations about the transition/inner transition elements:
(i) There is in general an
increase in density of element from titanium (Z = 22) to copper (Z =
29).
(ii) There
occurs much more frequent metal−metal bonding in compounds of
heavy transition elements (3rd
series).
(iii) The
members of the actinoid series exhibit a larger number of oxidation
states than the corresponding members of the lanthanoid series.
OR
(a)
Complete the following chemical equations for reactions:
(i)
(ii)
(b)
Give an explanation for each of the following observations:
(i) The
gradual decrease in size (actinoid contractions) from element to
element is greater among the actinoids than among the lanthanoids
(lanthanoid contraction).
(ii) The greatest number of
oxidation states are exhibited by the members in the middle of a
transition series.
(iii) With the
same d-orbital
configuration (d4)
Cr2+
ion is a reducing agent but Mn3+
ion is an oxidising agent.
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- Question 30
(a)
Illustrate the following name reactions by giving example:
(i)
Cannizzaro’s reaction
(ii)
Clemmensen reduction
(b) An organic compound A
contains 69.77% carbon, 11.63% hydrogen and rest oxygen. The
molecular mass of the compound is 86. It does not reduce Tollen’s
reagent but forms an addition compound with sodium hydrogen sulphite
and gives positive iodoform test. On vigorous oxidation it gives
ethanoic and propanoic acids. Derive the possible structure of
compound A.
OR
(a)
How are the following obtained?
(i)
Benzoic acid from ethyl benzene
(ii)
Benzaldehyde from toluene
(b)
Complete each synthesis by giving the missing material, reagent or
products:
(i)
(ii)
(iii)
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