No. of Printed Pages 4 IMeR-ooal
P.G. DIPLOMA IN ANALYTICAL CHEMISTRY
(PGDAC)
Term-End Examination 00764 December, 2016
MCH-003 SPECTROSCOPIC METHODS
Time hours Maximum Marks: 75
Note: Answer any Jive questions. All questions carry equal marks.

1. Answer any Five of the following: 5x3=15 What is plane polarised light? How is it obtained? Molecules show broad spectral bands whereas atoms give line spectra. Explain. What are the different types of transitions involved in uv-visible, infrared and microwave spectral techniques? Draw a labelled sketch of hollow cathode lamp and explain its use in AAS. Explain the variation in the position of the OH signal in the NMR spectrum of phenol as a function of concentration.
Write the various factors affecting fluorescence.


2. Draw a generalised molecular orbital energy level diagram showing possible transitions in organic compounds. Indicate various transitions observed for acetone in the diagram. 5

Define molar absorbance and transmittance and explain the relationship between the two. Calculate the transmittance of a solution having A =0.2. 5

What are the advantages of FT-IR spectrometer over dispersive IR spectrometer? 5

3. Explain various types of stretching and bending vibrations by considering suitable examples of AB2-type molecule. 5

A 6.5 x M solution of copper complex taken in a 1 cm cuvette showed the absorbance of 0.85 at Amax 580 nm. Another solution of unknown concentration measured at the same Amax showed the absorbance of 0.68. Calculate the concentration of the unknown solution. 5

Explain the nature of excitation and emission fluorescence spectra of 9-methylanthracene. Why does fluorescence occur at longer wavelengths than the absorption? 5

4. Explain fluorescence quenching and write the Stem-Volmer equation for it. Define quantum yield. 5

Describe the applications of fluorimetry in the analysis of NO -N02 as atmospheric pollutants. 5

Draw a schematic layout of fluorimeter. Write the sources and detectors commonly used in the fluorimeters. 5


5. Explain the characteristics of atomic spectrum in terms of position, intensity and spectral line width of signal. 5

Define flame. Explain how different combinations of fuel gases and oxidants give different flame temperatures. 5

Explain the basic principle of atomic fluorescence spectrometry. Write down the equation relating fluorescence intensity with concentration and draw the calibration plot. 5

6. Discuss the merits and limitations of atomic fluorescence spectrometric method in quantitative analysis. 5

Discuss briefly GFAAS. Explain how the signal obtained in GFAAS is different from that obtained in flame AAS. 5

Explain various types of interferences in atomic absorption spectrophotometry. How can the interference of phosphate be eliminated or minimized in the determination of calcium? 5

7. In what respects is Atomic Emission Spectrometry different from AAS. Describe in brief, the AES based plasma sources. 5

State three groups in which all nuclei may be classified on the basis of spin quantum number. Explain why 1H, 13C, 19F show NMR whereas 12C and 160 do not. 5

List all the essential components of mass spectrometer. Draw a schematic sketch of magnetic sector mass analyzer. 5

8. Define Index of Hydrogen Deficiency (IHD). Calculate IHD for C7H7NO and predict if it is unsaturated. 3

An organic compound with molecular formula C8H802 shows the following spectral characteristics
Mass spectrum. shows molecular ion peak at 136 and other fragmentation peaks at m/z 119,91 and 45.

(ii) Electronic spectrum shows an intense band at 230 nm.

(iii) Infrared spectrum shows an intense peak at 1700 and a broad band at 3000 cm^-1.
NMR spectrum shows a triplet at about S2.3, a multiplet at S7.4 -7.9. Also a singlet is observed at S10.5.

Interpret all the observations by assigning all the spectral peaks. Identify the compound and assign the structure. 12