In June ’18 we had the opportunity to again host the Research Experience for Teachers (RET) group in a hands-on
demonstration of corrosion testing in the Environmental Lab of MEC.
In this experiment the participants explored the potentials of various electrodes in comparison with a reference electrode. The reference electrode is a Copper-Copper(II) Sulfate Electrode (CSE), which utilizes the redox half-reactions between the metal (copper, or Cu) and one of its salts (copper (II) sulfate, or CuSO4). This particular kind of reference electrode is used commonly in taking field measurements of the electrochemical features of pipelines subject to corrosion.
The reference electrode is used to measure each half-cell potential in an electrochemical cell. By measuring this half-cell potential, we can construct a body of data which can be used to determine whole-cell potentials in electrochemical cells. Additionally, it can be determined which of the two substances will corrode when they form an electrochemical cell and a redox (reduction-oxidation) reaction takes place.
The corroding substance, which loses oxidized metal ions to solution through this process, is called the anode. The other substance, which actually has metal ions added to its solid bulk as they are reduced simply to metal atoms, is called the cathode.
In order to establish a traditional electrochemical cell, a few things must be in place: (1) two different metals in a solution of metal cations; (2) a conductive pathway allowing electron flow between the solid metals (usually a wire or cable); and (3) a salt bridge allowing the passage of ions into either metal cation solution without permitting the mixture of these solutions. In this activity, the last requirement was modified by placing both electrodes into the same water bath and allowing the cation solutions to mix. In the “real world” (i.e. in the field), the physical proximity of the electrodes and the ionic permeability of the soil, water, etc. between them places an electrochemical cell’s “salt bridge” presence somewhere between the set-up including the salt bridge and the freely mixing set-up in this experiment.