Converting Reference Electrode Potentials

When reading the literature we often find that the used reference electrode is different to the one we've used for an experiment. Converting between different reference electrodes isn't difficult but it is slightly error prone. For example, if a potential is measured as being at +0.1V (vs SCE) and we want to know what potential this is against a saturated Ag/AgCl electrode how can we do the conversion? At 25oC the SCE is +0.241 V (vs SHE) and the Ag/AgCl Sat. is +0.199 V (vs SHE). The simplest way forward is to draw out the different potential scales, as shown below, this way we're less likely to make a mistake when adding and subtracting the relevant potentials. If you click 'convert' on the calculator below, the measured potential is marked up on the scale and we can see that for the above problem the converted potential is +0.142 V (vs Ag/AgCl Sat.) i.e. 0.1 +0.241 -0.199 = +0.142.

Just be aware that the electrode values for different systems can vary a little between reports in the literature. This seems to be especially true for the Mercury/Mercury Sulphate (Sat.) electrode where Bard and Faulkner give a value of +0.64V vs SHE and The Analytical Handbook gives a value of +0.65 V vs. SHE. For most other reference electrodes Ives, David J. G., and George J. Janz. Reference Electrodes, Theory and Practice. New York: Academic, 1961. tends to be the primary literature source.

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Calculator (@25oC)