This laboratory exercise is an introduction to spectrophotometry suitable for college freshmen and high school students. It involves food dyes and brown M&M candy. The spectra of "primary" dyes are measured and represented graphically as absorbance vs wavelength to show that minimum absorption of light occurs in the spectral region corresponding to the color of the dye. The spectra of dye combinations illustrate the fact that some common colors are actually mixtures of colors. Finally, the Beer-Lambert law is verified by using the single-wavelength absorbance (620 nm, blue) of mixtures. This project illustrates the absorption of light by substances and its dependence on wavelength, the change of light absorption with the concentration of dissolved substance (Beer-Lambert law), and the explicit correspondence of colors with spectral features. It uses safe chemicals and connects everyday objects and substances with laboratory measurements.
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