M.Sc. (Semester IV) (CBCS) Examination Nov/Dec-2018
Physical Chemistry
MOLECULAR STRUCTURE II
Time: 2½ Hours
Max. Marks: 70
Instructions: Attempt in all five questions. Section I is compulsory Attempt any two questions from section II and section III. Answer to all questions (Section II and III) should be written in same answer book. All questions carry equal mark. Figures to right indicate full marks. Use of log table and calculator is allowed.
Section I
Q.1
Answer the following:
14
Write and expression for the average dipole contribution, according to Debye treatment.
Even through B-Cl bond is polar why BCl3 molecule is non polar?
Write the expression for relating magnetic susceptibility.
What is the advantage of Curie balance?
Give any two examples of nuclei with zero spin. What is the spin value of 16O nucleus?
Complete the equation.
Define spin-spin relaxation.
The shielding constant of proton decreases as the electronegativity of the atom to which the proton is attached increases. True or false.
Although the abundance of 13C is less abundant than 12C only 13C is used to obtain NMR why?
If the e.s.r. signal of an electron consists of four signals calculate the number of equivalent protons with which it will be interacting.
What is the value of g-factor for free electron?
Define Doppler broadening in Mossbauer spectroscopy.
The main factor on which chemical shift in Mossbauer spectroscopy depends is the around the nucleus.
Does the chemical shift in Mossbauer spectroscopy depends on the radius of the nucleus in the excited state?
Section II
Q.2
Derive Debye equation for molar polarization of a molecule.
07
Explain the Ebert's methods of determining dipole moment.
07
Q.3
Derive an expression for magnetic moment, according to Langevin theory of paramagnetism.
07
Explain the Gouy balance method of determining magnetic susceptibility.
07
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SLR-VF-172
Q.4
For an AX molecule explain the splitting of resonance energy levels (NMR signals) due to spin-spin coupling.
07
Explain the effect of field-induced dielectric circulation in ethyne and benzene molecules on the shielding and deshielding at a nearby proton.
07
Section III
Q.5
Describe the components of an ESR spectrophotometer with a schematic diagram.
05
The ESR spectrum of an unpaired electron interacting with two equivalent protons show how many lines and why?
05
The frequency for a free electron is 36.4 GHz. Calculate the magnetic field at which the ESR spectrometer is working. g=2.0,β=9.2732 ×10−24 JT−1, h=6.626 ×10−34 Js .
04
Q.6
Explain the recoilless emission and absorption of gamma rays in Mossbauer spectroscopy.
05
Explain how Mossbauer spectroscopy is useful in understanding electronic structure of molecules.
05
Calculate the recoil velocity and energy of a Mossbauer nucleus 67Zn if the emitted γ-ray has the frequency 1.84 x 1018 Hz 6.023 x 1023, h 6.626 x 10-34 Js, c 3.0 x 108ms-1).
04
Q.7
Write a note on any Three of the following.
14
Ionic character of a bond from dipole moment values
Curie-Weiss law and its verification
Spin- spin relaxation
Mossbauer sources