The Equilibrium Constant for Bromothymol Blue: A General Chemistry Laboratory Experiment Using Spectroscopy

Abstract

A simple, inexpensive, and environmentally friendly undergraduate laboratory experiment is described in which students use visible spectroscopy to determine a numerical value for an equilibrium constant, Kc. The experiment correlates well with the lecture topic of equilibrium even though the subject of the study is an acid−base indicator, bromothymol blue. The experiment gives excellent results and offers an inexpensive, zero-waste alternative to traditional equilibrium experiments, such as the Fe(SCN)2+ equilibrium.