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Quantitative Analysis by Spectrophotometric Methods

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Quantitative Analysis by Spectrophotometric Methods

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  • September 2008
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Abstract

In this experiment, the absorbance of KMnO4 was measured by spectrophotometric method to determine the molar concentration and the molar extinction coefficient of KMnO4. In part 1, in order to determine the maximum absorbance wavelength of KMnO4, we measured the absorbance of the sample solution which contains KMnO4 at the wavelengths between 330nm and 660nm, and plotted the λ and A points; the λmax was 530nm. In part 2, the effect of concentration on the absorbance was examined. We prepared five differently concentrated (but, same path length) solutions, and measured the absorbance of them at the λmax(530nm) discovered in part 1; According to the results, higher concentrated solution had higher absorbance value. The extinction coefficient(ε) could be calculated from the results determined in part 2 and Beer’s Law; ε = 1.7 x 103. In part 3, the absorbance of the KMnO4 solution of unknown concentration was measured, and using Beer’s law and dilution equation, the initial concentration of the unknown was determined; The concentration of the solution (unknown # : 15) was calculated to be 3.3 x 10-3M.

Introduction
Our eyes are sensitive to light which lies in a very small region of the electromagnetic spectrum labeled "visible light". This "visible light" corresponds to a wavelength range of 400 - 700 nanometers (nm) and a color range of violet through red. The human eye is not capable of "seeing" radiation with wavelengths outside the visible spectrum. The visible colors from shortest to longest wavelength are: violet, blue, green, yellow, orange, and red. Ultraviolet radiation has a shorter wavelength than the visible violet light. Infrared radiation has a longer wavelength than visible red light. The white light is a mixture of the colors of the visible spectrum. Black is a total absence of light. Figure 5.1 The electromagnetic spectrum.

Although visible light acts as a wave in some respects, it also displays properties characteristic of...

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