civil services mains 2009

CHEMISTRY

Paper I

Time Allowed Three Hours Maximum Marks 300

INSTRUCTIONS

Each question is printed both in Hindi and in
English.

Answers must be written in the medium
specified in the Admission Certificate issued
to you, which must be stated clearly on the
cover of the answer-book in the space provided
for the purpose. No marks will be given for
the answers written in a medium other than
that specified in the Admission Certificate.

Candidates should attempt Questions no. 1
and 5 which are compulsory, and any three
of the remaining questions selecting at least
one question from each Section.

The number of marks carried by each
question is indicated at the end of the
question.

Symbols and notations carry usual meaning,
unless otherwise indicated. Coordinate
diagrams, wherever required, are to be plotted
on the answer book itself and not on separate
graph sheet.

Assume suitable data if considered necessary
and indicate the same clearly.

SECTION A

I. Answer any three of the following 20x3=60

Give the Schrodinger's wave equation for H-atoms
in cartesian and polar co-ordinates. With the help
of a diagram show the relation between the two
co-ordinates.

Explain on the basis of MO theory, why:
Liquid oxygen sticks to the poles of a magnet
while liquid nitrogen does not do so.
He2 and Be2 molecules do not exist.
The bond order in oxygen is while that of
nitrogen is 3.
Hydrogen molecule is more stable than H2+
ion.
Derive Bragg's equation. Using X-ray powder
pattern of a compound describe how do you
calculate the spacing between the planes.
One mole of a perfect gas is ten-fold expanded
isothermally and reversibly at 300 K Calculate
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2. What do you mean by quantum numbers? Discuss
different types of quantum numbers and their
significance. 20
Define dipole moment.
Explain the following
Why is dipole moment of BF3 zero
Why is dipole moment of NH3 greater than
that of NF3
Why does S02 have dipole moment while CO2
does not? 20
Derive an expression to estimate the frequency of
collisions of gas molecules with a surface. Describe
the relaxation method for studying fast reactions. 20

3. What are stoichiometric and non-stoichiometric
defects Explain Schottky defects and Frenkel
defects and mention their consequences. 20
Derive an equation for surface tension exerted by
a liquid in a glass capillary tube placed in ihe
liquid when there is a rise. 20
Which among the following are intensive
properties pressure, volume, temperature,
internal energy, free energy and chemical
potential? 20
Define Gibbs free energy function. Explain
its significance.

4.(a)show that 20
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(i)The vapour pressures of water at 298 K and
308 Kare 3167 Pa and 5599 Pa respectively.
Calculate the enthalpy of vaporisation of
water.
Define excess free energy. What 1s its
significance 20
Nitrogen gas gets cooled as it expands
whereas hydrogen gas gets warmer as it
expands. Justify the observation.
The standard free energy change for the
following reaction is 8·7 kJ mol-1
2 C (graphite) 2 H20 CH4 CO2
Calculate the equilibrium constant of the
reaction at 900 K 20

SECTION B

5. Answer any three of the following 20x3=60

Define transport number of anion and
describe how it is measured.
Explain the basis of polarography. How is it
used in diffusion measurements
What is the principle behind ion selective
electrode and how is it used as a reference
electrode?
Define overpotential and exchange current
density.
Derive the rate constant of a second order reaction
when
two different reactants have same initial
concentrations.
two different reactants have different initial
concentrations.
Explain the pattern of splitting of d orbitals
in a square planar ligand field.
Calculate the Crystal Field Stabilisation
Energy and Spin-only Magnetic Moment of
[co(NH3)6]cl2
Mention the most stable oxidation state of
each of the metals Ce, Eu, Th, U and Pu.
''Magnetic susceptibility measurements are
of little use i n the structural elucidation of
lanthanide complexes." Justify the
statement.

6. Explain collision theory of reaction rates. What are
the factors which cause failure of this theory in
certain cases How do you make allowance for the
deviation from the ideal behaviour?
Describe the structure of electric double
layer and define outer potential and inner
potential.
Calculate the emf of the following cell and
predict whether the given cell
representation is correct or wrong. If wrong,
write the correct reaction.
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What are photochemical reactions
Explain quantum efficiency.
The quantum efficiency of the reactions
between hydrogen and chlorine 1s 105
whereas that between hydrogen and
bromine is 0·01. Explain the reason for this
difference. 20

7. Derive an equation for Langmuir's adsorption
isotherm. Discuss the causes for deviations
observed. 20
What are prosthetic groups of cytochromes
and haemoglobin
Taking into consideration electron transfer
and catalytic function, write 1n brief on
ferrodoxins. 20
Explain why octahedral Co(II) complexes
have rather higher magnetic moment than
tetrahedral Co(II) complexes.
Explain the origin of the colour of
permanganate. 20

8. Write IUPAC nomenclatures of
K3[Fe(CN)5NO]

[Co(en)2C12 Cl
[PtCl 4
Explain the terms 'chelate effect' and
'lability' in complexes with examples.
Explain the structure and bonding in
Hexachl orocyclotriphosphazene
Xenon hexafluoride.
Explain the salient fe atures of the structure of
[Re2cl8]2- and H2Ru6(CO)18.

Note English version of the Instructions is printed on
the front couer of this question paper.