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Experiment 34 Spectroscopy 2: Use of Visible Spectroscopy in Color Determination

The student is directed to read and understand the portion of this manual that introduces the student to spectrophotometry (Background Knowledge in Experiment 33), particularly that on ultraviolet (UV)–visible spectroscopy. The various chromophores that are present on a molecule can often be determined from the absorption band so that a scientist can establish some information about the structure of materials. Examples of some common chromophores are shown in Figure 34.1. The easiest way to identify a chromophore is by comparison to a database of known wavelengths for specific chromophores. Dyes, particularly solutions, are readily examined by visible spectroscopy using the transmission method. Even mixtures of dyes can often be determined by careful examination of the questioned spectra and the reference database. In many cases the dye mixtures can be quantitated to determine the concentration of each in the solution. This multicomponent quantitative analysis is beyond this introductory experiment; however, interested students are referred to the literature.