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Q.1.(b)Give principle of UV-visible spectroscopy, Explain why cellulose is white in colour, picric acid is yellow and aromatic diazotization and coupling produces different shades.
Ans.1. (b)The wavelength range of UV radiation starts at blue end of the visible light (above 4000 A°) and ends at 2000 A°. However, the wavelength of visible radiation starts at 8000 A° and ends at 4000 A°. Spectroscopically, visible light acts in the same way as UV light.
Q.1. (c) Discuss how certain compounds produce fluorescence or phosphorescence when exposed to electromagnetic radiation. How this property is exhibited only by organic compounds with certain structural specifity? Explain
Ans.1.(c) When electromagnetic radiation passes through matter, a variety of phenomena may occur. One of them is; in some cases, the molecules after absorbing radiation become excited but they do not lose energy very quickly but with some delay. In such cases, the energy is re-emitted as radiation, usually of longer wavelength: than was originally absorbed. This phenomenon is termed as fluorescence. If in some cases, there is a detectable time delay in re-emission, the phenomenon is termed as phosphorescence.
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