From Voltage to Absorbance and Chemical Kinetics Using a Homemade Colorimeter

摘要

The use of the Beer-Lambert law in spectroscopy is the core of standard methods for determining a chromophore concentration in a solution. Its application requires an understanding about interaction of light with a colored solution and the use of light emission and light detection devices. We build here a simple electronic circuit formed of light-emitting diodes and light-dependent resistors that can be used for measuring chromophore concentrations during experiments focused on chemical kinetics: decolorizing of phenolphthalein in a basic solution, and reduction of methylene blue by ascorbic acid. From the chemical point of view, the goal is to determine experimentally the rate law. In addition, students understand, using inexpensive electronics, the basic design of a spectrophotometer to achieve successful measurements of absorbance.