IGNOU MSCANCHEM MCH 3 Spectroscopic Methods Solved Assignment ENGLISH

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MCH 003 (January 2026) - ENGLISH

TUTOR MARKED ASSIGNMENT SPECTROSCOPIC METHODS

Course Code: MCH-003

Assignment Code: MCH-003/TMA/2026

Maximum Marks: 100

Note: Answer all the questions given below.

1. 

a) What is wave number? How is it related to wavelength?

b) What is unpolarised light? How can it be polarised?

c) Calculate the absorbance and transmittance of a 0.002 40 M solution of a substance having a molar absorptivity of 313 M¹ cm²¹ in a cell with a path length of 2.00 cm.

2.

a) The UV-VIS spectrum in gaseous phase is observed to be a band spectrum whereas in solution phase it is a smooth and continuous absorption peak. Explain.

b) Discuss the factors responsible for the deviation from Lambert-Beer's law.

3.

a) What is the role of a detector in a spectrophotometer? Explain the principle of photomultiplier tube as a detector.

b) Discuss the standard addition method for generating a calibration curve. Under what conditions does this method become important?

4.

a) What is the selection rule for the vibration spectroscopy? Explain the origin of fundamental, first overtone and second overtone in the IR spectrum.

b) Describe is KBr pelleting method for handling solid samples in IR spectroscopy.

c) Calculate the number of vibrational modes for a molecule of methane.

5.

a) Explain the origin of Rayleigh and Raman lines with the help of an energy level diagram.

b) Discuss different modes of relaxation for an electronically excited molecule using the Jablonski diagram. 

6.

a) Discuss different factors affecting fluorescence.

b) Discuss the fate of a sample introduced in the flame.

7.

a) Discuss the merits and demerits of Flame photometric method.

b) Enlist different pathways for atomic fluorescence emission and explain Stokes direct line fluorescence method.

8.

a) The choice of proper reagents and techniques of decomposition and dissolution of the sample is a critical step for the success of AAS determination. Explain the preparing sample for AAS using microwave digestion system.

b) List the characteristics of an ideal atomization-excitation source.

9.

a) Draw a schematic layout of different components of an ICP-AES spectrometer and briefly state the role of each component.

b) Explain different relaxation mechanisms by which these operate to maintain population difference in nuclear spin states in NMR.

10.

a) What are isotopic peaks? Discuss the importance of isotopic peaks in mass spectrometry.

b) The important spectral details of an organic molecule having a molecular formula C4H8O are as follows:

Mass: (Prominent peaks at m/z 29, 43 (base peak); 57 and 72 (M+)

IR: (2950 cm¯¹ (medium); 1718 cm¹ (strong); 1370 cm¹ (medium); and 1150 cm (medium))

NMR: (δ=0.92 (3H, triplet); δ= 1.95 (2H, singlet) and δ= 2.6 (3H, quartet))

Determine the structure of the organic molecule.

MCH 004 (July 2025 - January 2026) - ENGLISH

Tutor Marked Assignment

Spectroscopic Methods

Course Code: MCH-003

Assignment Code: MCH-003/TMA/2025-26

Maximum Marks: 100

Note: Attempt all the questions given below.

1.

a) Define electromagnetic radiation in terms of the wave mechanical model. Compute the energy of a photon corresponding to 102.6 MHz frequency.

b) The transmittance of a solution, containing 7.3 mg of an potassium dichromate per 100 cm³, taken in a cuvette of path length of 1 cm is measured at 455 nm. If the percentage transmittance found to be 6, calculate the molar absorptivity of the oxidizing agent.

2.

a) What are monochromators? Describe the working of a grating monochromator. In what way is the standard addition method of calibration in UV-VIS spectrophotometry better than the standard solution method?

b) Explain the origin of Raman spectrum in terms of quantum theory of radiation. State the 'Rule of mutual exclusion'. What is its significance?

3.

a) Explain the origin of fluorescence and phosphorescence spectra in terms of Jablonski diagram. What is meant by fluorescence quenching? How does it affect the quantum yield of a fluorescence emission?

4.

a) What is chemiluminescence? Describe an analytical application of chemiluminescence in the area of environmental pollution measurement.

b) What is meant by room temperature phosphorescence? How is it achieved?

5.

a) Briefly explain the origin of atomic spectrum. Explain why the atomic spectra are line spectra whereas the molecular spectra are band spectra

b)

Discuss the fate of analyte sample in the flame of a flame photometer. What is internal standard method? Under what conditions is it used?

6.

a) Briefly explain the different types of spectral interferences observed in flame photometry.

b) Explain different pathways of atomic fluorescence emission. In what way is halogen cathode lamp (HCL) better than a continuous source for atomic fluorescence measurement?

7.

a) Explain the principles of atomic absorption spectrophotometry and atomic emission spectrometry.

b)

Enlist the advantages of GFAAS over FAAS and the advantage of line sources over continuum sources for AAS.

8.

a)

Enlist different components of an ICP torch. What makes argon a good choice for the plasma gas?

b)

What are different types of instruments used for ICP-AES? Which of these is better and why? Explain.

9.

a Explain spin-spin splitting and Larmor precession the following terms in the context of NMR spectrometry.

b) What is the principle of mass spectrometry? Explain how it is different from other spectrometric methods.

10.

a) Explain McLafferty rearrangement with the help of a suitable example.

b) What kind of structural information is available from UV, IR, NMR and Mass spectra of an organic compound?

MCH 3 2025 - English

Tutor Marked Assignment

MCH-003: Spectroscopic Methods

Course Code: MCH-003

Assignment Code: MCH-003/TMA/2025

Maximum Marks: 100

Note: Answer all the questions given below.

1. a) Define electromagnetic radiation in terms of the wave mechanical model. State the necessary condition for a molecule to show IR spectrum. Will HCl show IR spectrum?

b) The transmittance of a solution, containing 7.3 mg of potassium dichromate per 100 cm³, taken in a cuvette of path length of 1 cm is measured at 455 nm. If the percentage transmittance found to be 6, calculate the molar absorptivity of the oxidizing agent.

2. a) What are monochromators? Describe the working of a grating monochromator. In what way is the standard addition method of calibration in UV-VIS spectrophotometry better than the standard solution method?

b) Explain the origin of Raman spectrum in terms of quantum theory of radiation. State the "Rule of mutual exclusion'. What is its significance?

3.a) Explain the origin of fluorescence and phosphorescence spectra in terms of Jablonski diagram. What is meant by fluorescence quenching? How does it affect the quantum yield of a fluorescence emission?

b) The experimental set up for the fluorescence spectral measurement is different from that for the absorption measurement. Comment on the statement. Why do we need to modify the instrumental set up for the fluorescence spectrometer to make phosphorescence measurements?

4.a) What is chemiluminescence? Write an analytical application of chemiluminescence in the area of environmental pollution measurement.

b) Describe the application of fluorescence measurements in medical diagnosis by taking the example of blood glucose determination.

5. a) Briefly explain the origin of atomic spectrum. Explain why the atomic spectra are line spectra whereas the molecular spectra are band spectra.

b) Discuss the fate of analyte sample in the flame of a flame photometer.

6. a) Explain the different types of spectral interferences observed in flame photometry.

b) Explain different pathways of atomic fluorescence emission. In what way is halogen cathode lamp (HCL) better than a continuous source for atomic fluorescence measurement?

7.a) Explain the principles of atomic absorption spectrophotometry and atomic emission spectrometry.

b) Why line sources are preferred over continuum sources for AAS? Enlist the advantages of GFAAS over FAAS.

8 a) Enlist different components of an ICP torch. What makes argon a good choice for the plasma gas?

b) Describe the acid digestion method of solution preparation in AES.

9. a) Explain the following terms in the context of NMR spectrometry.

• Chemical shift
• Spin-spin splitting
• Larmour precession

b) FT-NMR is better than CW-NMR. Comment on the statement. What is the principle of mass spectrometry? In what way is it different from other spectrometric methods?

10.a) Explain Mc Lafferty rearrangement with the help of a suitable example. Calculate IHD for the molecule having the molecular formula, C₂H₂O₂

b) What kind of structural information is available from UV, IR, NMR and Mass spectra of an organic compound?

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