Lab 6 Absorption Spectroscopy

Lab 6 Absorption Spectroscopy - Absorption Spectroscopy-...

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Absorption Spectroscopy- Lab 6 Author: Holly Polk Lab Partners: Jim Hernandez, Vanessa Jordan, and Dominic Pisciotta Instructor: Yisheng Xu Chemistry Lab 151, Section 001 Date Work Performed: March 3, 2008 Date Report Submitted: March 10, 2008 Abstract: The main objective of this experiment is to use absorption spectroscopy and Beer-Lambert’s law to identify the amount of dye present in a commercial food product and evaluate its safety. The dye content of the Raspberry Lemonade sample was 2.21 e-3 grams per liter, and the amount of Raspberry Lemonade that would have to be consumed to reach an LD50 of exposure is 2, 710 Liters. The dye content of the Strawberry Kool-Aid sample was 3.93e-03 grams per liter, and the amount of Raspberry Lemonade that would have to be consumed to reach an LD50 of exposure is 1,526 Liters.
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Introduction The main objective of this experiment is to identify the amount of dye present in a commercial food product and evaluate its safety. In this experiment, a serial or parallel dilution of a solution of the pure dye will yield solutions of a known concentration. Absorption measurements of samples will be made using a spectrophotometer and a calibration plot may be produced. The plot can then be used to convert absorption measurements of the samples into molar concentrations. Molar concentrations may be converted into grams, then those may be related to the original weight of the sample and the dye’s LD50. The LD50 is a way of expressing the danger of a chemical: it is the amount of that chemical that will cause death in 50% of the population. A Beer’s law analysis will be used to determine a solution’s concentration. Beer’s law is an empirical relationship that relates the absorption of light to the properties of the material through which the light is traveling. The formula is A=ebc, where A is absorbance (no units, since A = log10 P0 / P ), e is the molar absorbtivity with units of L mol-1 cm-1, b is the path length of the sample - that is, the path length of the cuvette in which the sample is contained. We will express this measurement in centimeters. c is the concentration of the compound in solution, expressed in mol L. Spectroscopy is a good way to make direct measurements because light absorption is a molecular phenomenon. Light absorption is a selective process and only certain wavelengths may be absorbed by certain molecules. Molecular absorption is quantitative, and the amount of light absorbed is directly proportional to the number of molecules. We use white light so that we can determine all color wavelengths in the dye. White light has more wavelengths than other single color lights. We also use a prism as a light dispersion device so that you can see the rainbow of colors. The third part of spectroscopy is a slit or wavelength selector to check a
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This note was uploaded on 02/17/2009 for the course CHEM 151 taught by Professor Staff during the Spring '08 term at University of Arizona- Tucson.

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Lab 6 Absorption Spectroscopy - Absorption Spectroscopy-...

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