pH Dependent Redox Couple: An Illustration of the Nernst Equation

Electrochemical reactions depending on pH are ideal for illustrating the Nernst equation for undergraduate laboratories. An experiment utilizing the hydroquinone/quinone redox was developed which follows the potentials of the anodic and cathodic cyclic voltammetric waves as a function of solution pH. The 1mM hydroquinone solutions are prepared in phosphate/acetate mixed buffers with pH between 1-6. Cyclic voltammograms were obtained for each solution. As solution pH increases, the anodic and cathodic potentials shift cathodically as predicted by the Nernst equation. Plots of peak potential vs. pH were linear and showed that the hydroquinone/quinone redox reaction involves two electrons.