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Indian Forest Service (Main) =e
Examination, 2024 JBNV-U-CHMY
CHEMISTRY
Paper - I
Time Allowed : Three Hours Maximum Marks : 200
Question Paper Specific Instructions
Please read each of the following instructions carefully before attempting
questions:
There are EIGHT questions in all, out of which FIVE are to be attempted.
Questions No. 1 and 5 are compulsory. Out of the remaining SIX questions, THREE are
to be attempted selecting at least ONE question from each of the two Sections A and B.
Attempts of questions shall be counted in sequential order. Unless struck off, attempt of a
question shall be counted even if attempted partly. Any page or portion of the page left
blank in the Question-cum-Answer Booklet must be clearly struck off.
All questions carry equal marks. The number of marks carried by a question/part is
indicated against it.
Unless otherwise mentioned, symbols and notations have their usual standard meanings.
Assume suitable data, if necessary, and indicate the same clearly.
Neat sketches may be drawn, wherever required.
Answers must be written in ENGLISH only.
h = 6-626 x 1074 Js kp = 1:38 x 10° JK
R=8314 JK! mol! n= 3-14
c=3x10°ms? F = 96500 C mol?
Na = 6-023 x 10” mol 1 atm = 101325 Pa
m, = 9:1x 10°! kg
JBNV-U-CHMY 1
SECTION A
Ql. (a) For a free particle, show how the time-independent Schrodinger
equation gives a solution to explain de Broglie relation.
(b) Fora reaction
He (g) + ; Oz (g) ———> H20 (g)
calculate standard entropy change of the reaction at 373 K, using data
as below :
Given : Seog for H20 (g) = 188-825 J/K/mol
Og (g) = 205-138 J/K/mol
Hg (g) = 1380-684 J/K/mol
Molar heat capacities at constant pressure of
H20 (g) = 33:58 J/K/mol
Oo (g) = 29:37 J/K/mol
Hg (g) = 28-84 J/K/mol
(c) An absorbing substance is exposed to a light of wavelength 400 nm using
a 100 mW laser source for 50 minutes. The intensity of the transmitted
light is 40% that of incident light. As a result, 0-4 mmol of the absorbing
substance is decomposed. Determine the primary quantum yield of this
photochemical reaction.
(d) Equivalent quantities of NH3 and HCl form a one-component system,
but when slight excess of NHg or HCl is added, it becomes a
two-component system. Explain.
(e) Ina galvanic cell, if Eiy3+ jay and Eye? Mg 27@ - 1-66 and — 2:37 V
respectively, calculate the standard free energy change for the cell
reaction and also calculate the equilibrium constant for the cell
reaction.
JBNV-U-CHMY 2
Q2.
Q3.
(a)
(b)
(c)
(d)
(a)
(b)
Determine the most probable radius at which electron will be found
when it occupies 1s orbital of Li2* ion. 10
Derive an expression to calculate the number of vacancies per mole of
metal atoms at a given temperature. 15
Assume the following :
(i) Contribution to entropy by vibration of atoms is small and can be
neglected.
(ii) Use E, as the energy required to create one mole of vacancy.
The rate constant for the first-order decomposition of ethylene oxide into
CHy, and CO follows the equation :
log k (in s- ) = 14-34 - (1-25 x 104K) /T
Calculate :
(i) the activation energy of the reaction.
(ii) the rate constant at 700 K.
(iii) the frequency factor, A. 10
A metal M, can displace hydrogen but another metal Mg can not. Metal
Mg can displace another metal Mg from its salt solution. Arrange the
metals Mj, Mo, Mg in decreasing order of the E° values. Justify. 5
Explain the thermodynamic formulation of the activated complex theory
for a simple bimolecular reaction. Draw energy profile diagram for an
exothermic and an endothermic reaction. 15
Consider an atomic crystal where N atoms are situated at lattice sites.
Assume all lattice sites are identical and each atom is vibrating with
same frequency, as a three-dimensional harmonic oscillator.
The partition function that satisfies this model is given as :
(Uy (_e7 Bhv/2 \3N
Q=e [oe Bhv
v > characteristic frequency of vibration of the atoms
Up > Sublimation energy at 0 K.
Bo =" where kp is Boltzmann constant
kp,T
Calculate the molar heat capacity of this atomic crystal from the given
partition function at higher temperature. (Assume constant volume) 10
JBNV-U-CHMY 3
Q4.
(c)
(d)
(a)
(b)
(c)
Consider a molecule ‘A’ in a solution undergoes the following steps when
it absorbs UV light of intensity I,,,.
I
) A+hv —2?8_, A*
k
Gi) A*+A —2-> Apo (dimerization)
(iii) A* —-3_, A + hv (fluorescence)
k
(iv) Ag ——‘4_, 2A (thermal decomposition)
Derive an expression for determining the concentration of Ag at
equilibrium, when the concentration of A is large.
Consider ‘A’ and ‘B’ are two metals with cubic unit cell. The powder XRD
pattern of ‘A’ gives XRD lines corresponding to (110), (200), (220), (311),
(400) and (331) planes, while the powder XRD pattern of ‘B’ gives XRD
lines corresponding to the planes of (110), (200), (211), (220), (801) and
(222). Comment on the type of space lattice in ‘A’ and ‘B’, and justify.
What fraction of space in the unit cell of ‘A’ is available for tightest
possible packing of its atoms ?
Draw the phase diagram of lead-silver system. Explain its significance
in desilverization of lead.
Calculate the mean ionic activity coefficient y A of (i) NaCl at a molality of
0-01, and (ii) NagSO4 at a molality of 0-001 in aqueous solution at
25°C.
What is the meaning of isotherm ? Write BET equation and explain how
specific surface area of a solid is determined.
JBNV-U-CHMY 4
10
15
15
10
SECTION B
Q5. (a) Explain why LiF is less soluble than Lil in water. Using your
explanation, state, between CsF and CsI, which one would be more
soluble in water. 8
(b) Draw the structures of possible diastereoisomers of
ICo(NH3)2 (H2O)2 ClglCl. Among these isomer(s), which is/are optically
active ? 8
(c) Predict the structure of Co(CO)g with the help of 18-electron rule. What
differences do you expect in the C = O stretching frequency(ies) between
Co(CO)g and Mn(CO) 9 ? Explain.
[Atomic number of Mn = 25; Co = 27] 8
(d) Explain how ‘Relativistic effect’ contributes in ‘Lanthanide contraction’. 8
(e) | Write down the chemical equation for nitrogen fixation by nitrogenase
enzyme. Discussing the thermodynamic and kinetic aspects of the
reduction of No, state why nitrogen fixation requires an enzyme. 8
Q6. (a) Wi Showing the crystal field splitting, calculate the spin only
magnetic moment of [CoClyl? ~ and [Co(H20)¢l” *
(ii) The experimentally observed magnetic moment of which of these
two species would deviate more from the calculated spin only
value ? Explain your answer.
(iii) Colour of which of these two species would be less intense ?
Explain your answer. 5+5+5=15
(b) G) State the changes that occur in Hemoglobin molecule on
oxygenation.
(ii) What is ‘blue baby syndrome’ ? Why does it occur ?
(iii) What do you understand by ‘Haldane effect’? in relation to
oxygen-uptake proteins ? 7+-44-4=15
JBNV-U-CHMY 5
(ce) Predict the product(s) in the following reactions : 5x2=10
(i) RCOoH + HF (liquid) ———>
(ii) BF3 + HF (liquid) ———~>
in liquid NH.
Gii) — [PNHg))2* + Na 73 >
(iv) SO3 + HgSO, (liquid) ———>
(v) Clg + NHsg (liquid) ———>
Q7. (a) No and CO are isoelectronic but their Molecular Orbitals (MOs) are
different from each other. Drawing the MOs of both the molecules, state
with reasons the differences of these two MOs and their coordinating
ability. 15
(b) W@W Write the product of the following reaction :
Explain the ‘coordinative unsaturation’ and ‘oxidative addition’
in the above reaction. 5
(ii) Explain how the fluxional behaviour of the molecule
[ (ny! — Cs5Hs)y (n° — C5Hs)2 Ti] can be characterised. 10
(c) Explain why 2+ oxidation state is stabilized in Eu (At. No. 63). With the
help of your explanation, predict among Ce (At. No. 58), Tb (At. No. 65)
and Sm (At. No. 62), which one is most likely to show 2+ oxidation
state. 10
JBNV-U-CHMY 6
Q8. (a)
(b)
(c)
(d)
Calculate the temperature at which the average velocity of oxygen
equals to that of hydrogen at 20 K.
Using critical constants P, , V, and T, for a real gas that satisfies
van der Waals equation, find the critical compression factor of the gas
near critical point.
Among Ne and Ar, under similar conditions, whose standard molar
entropy is larger ? Explain.
Assume both Ne and Ar are perfect gases.
Why is yellow colour observed, when sodium chloride is heated in
sodium vapour ?
JBNV-U-CHMY 7
10
10
10
10
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