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Indian Forest Service• Examination .. · .L ···-··- I D-VSF-L-PUA I
CHEMISTRY
Paper I
I Time Allowed Three Hours I I Maximum Marks: 2001
INSTRUCTIONS
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.
All questions carry equal marks.
Marks allotted to parts of a question are
indicated against each.
Assume suitable data, if considered necessary,
and indicate the-same clearly.
Answers must be written in ENGLISH only.
Unless otherwise indicated, symbols and
notations have their usual meanings.
SECTION A
1.Attempt any four of the following
The vapour pressures of water at 298 K and 308 K are 3167 Pa and 5599 Pa respectively. Calculate the molar enthalpy of vaporisation of water.
Derive Bragg's equation. How do you calculate the spacings between the planes
Define eigen function and eigenvalue. Determine the eigenvalue of the function sie e ikx with operator d/dx
Absorption spectra of actinide elements comprises of very sharp lines. Assign the transition(s) responsible.
Calculate radial distance from the nucleus of hydrogen atom at which the given radial wave function for 2s orbital is zero. (Given, a0 52·9 x 10-12 <img src='./qimages/1337-1e.jpg'>

2.(a)State and explain the law of photochemical
equivalence. How are the discrepancies of this
law explained
(b)Volume of nitrogen gas at 1 atm and 273 K
required to cover 1 g of silica gel is 0·129 dm3
Calculate the surface area of the gel if
each nitrogen molecule occupies an area of 16·2 X 10-10 m2. 20

3.(a)Consider a galvanic cell that uses the following
reaction
2 Fe3+ 2 Fe2+ Cu2+
Given
<img src='./qimages/1337-3a.jpg'>
(i)Calculate the standard cell potential and
comment on your result.
(ii)Calculate the cell potential at 25°C that
has the following concentration values
1·0 x 10-4 0·25
[Fe 0·2 M 10
(b)Explain the differences between homogeneous
and heterogeneous catalysis with examples.
Enumerate the steps involved in
Langmuir- Hinshelwood catalysis. 20
4.(a)What are "excess-functions" Show that
<img src='./qimages/1337-4a.jpg'>
where symbols have their usual meanings. 20

(b)Equation for probability density, for the
Maxwell distribution of speed is
<img src='./qimages/1337-4b.jpg'>
From the above equation; derive the expressiOn
for the most probable speed. Show how
distribution varies with the temperature. 20

SECTION B
5. Attempt any four of the following
(a)Give 'spin only' formula for calculating magnetic
moment.How is this parameter affected by
variation of temperature Comment.
(b)What is residual entropy Why are certain
substances like CO and N2O associated with
residual entropy even at 0 K
(c)What are orthonormal wave-functions
Normalise the following wave-function for a
particle in one-dimensional box
<img src='./qimages/1337-5c.jpg'>
(d)The overall rate constant for a complex reaction
is where kl,k2 and k3 are the rate
constants, and El,E2 and E3 are the
corresponding energies of activation. Obtain the
expression for the overall energy of activation of
this reaction.
(e)What is a superacid Explain protonating action
of a superacid, giving suitable example(s) 10

6.(a)What are semiconductors Explain n-type and
p-type semiconductors. How does variation of
temperature affect their conductivity 20

(b)(i)Carbon dioxide has a linear structure
whereas sulphur dioxide is a bent molecule.
Explain, giving reason.
(ii)Explain lanthanide contraction. How are
properties of elements or 5d series
following lanthanides affected by this
contraction Explain.
7.(a)How does acid catalysis differ from proton
catalysis Illustrate giving mechanistic
pathways, the role of a metal ion acting as a Lewis acid catalyst in a biological reaction.
(b)Aqueous solutions containing Ti3+ ions are
reddish violet in colour; a single broad peak with
a maximum is observed at 20300 cm-1 Assign
the transition(s) taking place and explain the
observation.
8.(a)Starting with [ptCl4]2+ prepare diamminedichloroplatinum Name the isomer formed.
Choose the relevant starting material and write
all steps to get the other geometrical isomer of
the above product. 20
(b)When any alkali metal is dissolved in liquid
ammonia, a blue coloured, conducting and
paramagnetic solution is obtained.
Explain, giving reason, each of the above
observations. 20