Exp.9-dyes - Experiment THEORETICAL AND EXPERIMENTAL...

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THEORETICAL AND EXPERIMENTAL TREATMENT OF DYE MOLECULES Introduction Chem Connections When polychromatic light shines on atoms and molecules only certain frequencies of light are absorbed. When an atom or molecule absorbs light, the electrons are excited to a higher energy state. Given that only certain frequencies (or wavelengths) are absorbed, we can conclude that the electrons bound to atoms are quantized. This means that only a few energy transitions for the electron exist rather than an infinite number. A good overview of greater details of the theory related to this experiment is given in the previous experiment, Exp. 8 Molecules and Light and the introduction to the experiment should be reviewed. In this experiment you will explore the light absorbing properties of molecules using several different methods. Initially you will predict the wavelengths of light absorbed just by visual inspection of the samples. Next you will calculate the expected wavelengths absorbed based on a quantum mechanical model of electrons. Finally, you will measure the actual absorbance spectra of the molecules to see how well your predictions match experimental observations. Experiment 9
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Investigation I. Predicting the wavelengths absorbed The structures of the 6 dyes used in this lab are given below: Table 1: Structures of Dyes 1,4-diphenyl-1,3- butadiene 1,6-diphenyl-1,3,5- hexatriene 1,8-diphenyl-1,3,5,7- octatetraene 1,1’-diethyl-2,2’-cyanine iodide 1,1’-diethyl-2,2’- carbocyanine iodide 1,1’-diethyl-2,2’-dicarbocyanine iodide 1) Consider the 6 solutions of dyes in lab. Predict the color of light absorbed for each based on visual inspection. Table 2: Predicted Absorption Maximum Set Dye Molecule Predicted Color Absorbed 1,4-diphenyl-1,3-butadiene 1,6-diphenyl-1,3,5-hexatriene 1 1,8-diphenyl-1,3,5,7-octatetraene 1,1’-diethyl-2,2’-cyanine iodide 1,1’-diethyl-2,2’-carbocyanine iodide 2 1,1’-diethyl-2,2’-dicarbocyanine iodide I- I- Violet Indigo Blue Green Yellow Orange Red
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This note was uploaded on 10/12/2011 for the course CHEM 1A taught by Professor Nitsche during the Fall '08 term at University of California, Berkeley.

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Exp.9-dyes - Experiment THEORETICAL AND EXPERIMENTAL...

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