Reflectance Spectroscopy Using Wine Bottle Glass

M. GABRIELA LAGORIO

JOURNAL OF CHEMICAL EDUCATION

American Chemical Society

Lugar: Wisconsin; Año: 1999 vol. 76 p. 1551 - 1554

0021-9584

The determination of the concentration of light-absorbing species in heterogeneous media is increasingly relevant nowadays. Examples include photocatalysis (1) and solid-state photochemistry and photophysics (2, 3), where the actual number of absorbed photons makes the calculation of quantum yields possible. These determinations can be made by diffuse reflectance spectroscopy. Just as undergraduate students are routinely taught how to obtain an absorbance spectrum of a transparent homogeneous sample, they now also need to be taught how to evaluate absorbance in solids or suspensions where light scattering takes place. A few experiments using diffuse reflectance have been published for the undergraduate laboratory (4?9). Mostly, they have been concerned with instrumentation or with examples of applications. None of them have presented the theoretical basis of the technique. This paper describes an inexpensive diffuse reflectance experiment that illustrates how the absorbance or the number of absorbing species may be obtained for a solid or a suspension. The theoretical basis is established first; then the application is demonstrated by means of disposable glasses. Here, a piece of green glass from a wine bottle and any piece of colorless glass have been used. No toxic materials are involved in the experiment.