Exp4-chm171L - CHM171L / A11 Physical Chemistry Laboratory...

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CHM171L / A11 Physical Chemistry Laboratory 2 3 rd Quarter S.Y. 2010-2011 SPECTROPHOTOMETRY Austria, Maynard 1 , Co, Argenia B. 2 1 Professor, CHM171L/A31, School of Chemical Engineering, Chemistry and Biotechnology, Mapua Institute of Technology; 2 Student, CHM171L /A31 , School of Chemical Engineering, Chemistry and Biotechnology, Mapua Institute of Technology ABSTRACT The experiment aims to determine the wavelengths emitted by different set-ups and how are they affected by the concentration of solutions. The first one will be the visible light. The visible spectrum is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A solution has different absorbance depending on the wavelength emitted by the spectrophotometer. The Cobalt (II) Nitrate solution of different concentrations was loaded on the spectrophotometer and let the program plots the data. Exploring the data on the different wavelengths will give the corresponding absorbance. In the third part of the experiment, the relationship between concentration and absorbance was found: direct proportionality as explained by the Beer’s Law. INTRODUCTION In chemistry , spectrophotometry is the quantifiable study of electromagnetic spectra . It is more specific than the general term electromagnetic spectroscopy in that spectrophotometry deals with visible light, near- ultraviolet , and near- infrared . Also, the term does not cover time-resolved spectroscopic techniques. Spectrophotometry involves the use of a spectrophotometer. A spectrophotometer is a photometer (a device for measuring light intensity) that can measure intensity as a function of the light source wavelength. Important features of spectrophotometers are spectral bandwidth and linear range of absorption measurement. The extent to which a sample absorbs light depends strongly upon the wavelength of light. For this reason, spectrophotometry is performed using monochromatic light. Monochromatic light is light in which all photons have the same wavelength. In analyzing a new sample, a chemist first determines the sample's absorbance spectrum. The absorbance spectrum shows how the absorbance of light depends upon the wavelength of the light. The spectrum itself is a plot of absorbance vs wavelength and is characterized by the wavelength ( max) at which the absorbance is the greatest. λ The value of max λ is important for several reasons. This wavelength is characteristic of each compound and provides information on the electronic structure of the analyte. In order to obtain the highest sensitivity and to minimize deviations from Beer's Law (see subsequent pages on this topic), analytical measurements are made using light with a wavelength
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Exp4-chm171L - CHM171L / A11 Physical Chemistry Laboratory...

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