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Background

Cyclic voltammetry (CV) is popular for its relative simplicity and its high information content. It is used most often as a diagnostic tool for elucidating electrode mechanisms. Although it was first practiced at a hanging mercury drop electrode [ref. 1], it gained widespread use when solid electrodes like Pt, Au and carbonaceous electrodes were used, particularly to study anodic oxidations [ref. 2]. A major advance was made when mechanistic diagnostics and accompanying quantitations became known through the computer simulations in publications of Nicholson and Shain [ref. 3] and Feldberg [ref. 4]. Several monographs [refs. 5, 6] and texts [refs. 7, 8] provide excellent descriptive materials on fundamentals of CV. Example websites with content that complements this CV experiment are http://poohbah.cem.msu.edu/courses/cem419/, www.bioanalytical.com/mcns/EC_epsilon/Techniques/cycvolt.cv.html and http://poohbah.cem.msu.edu/courses/cem419/ Figures 1-6 in this latter site show diffusional profiles and analyses of cyclic voltammograms.

In this experiment, the basics of CV will be illustrated by looking at the one electron reduction of ferricyanide to ferrocyanide. This redox couple exhibits nearly a reversible electrode reaction without any complications of proceeding or post chemical reactions. Thus, ferricyanide/ferrocyanide couple has been a popular choice through the years to use as a standard to demonstrate CV, as evidence by experiments described in several of the references listed herein.

There are not many such ideal electrode reactions. For example, the oxidation of ferrocene to ferricinium ion is a fast reversible electron transfer reaction at most electrodes. However, ferrocene is water insoluble necessitating the use of a non-aqueous solvent like acetonitrile. On the other hand, ferrocene carboxylic acid (FCA) and ferrocene acetic acid (FAA) are water soluble and undergo a facile one-electron oxidation to the ferricinium state. An optional experiment with FCA is proposed at the end of the main experiment.

The usual laboratory safety practices apply in the conduct of this experiment. Consult with the laboratory supervisor about proper use of chemicals and instrument.