Converting Potentials Between Different Types of Reference Electrodes
See also: Saturated calomel electrodeOften a reduction potential is quoted as measured against a different reference electrode than the one desired and it becomes necessary to convert to the desired reference potential. Alternatively, it may be necessary to convert measurements to the standard reduction potential for reporting purposes. This is easily done by recognizing that the observed potential represents the difference between the potential at the sensing electrode and the potential at the reference electrode, i.e.
Where is the observed reaction, is the reference used in experiment, and is the reference that is desired. The voltage relationships for several different reference electrodes at 25 °C can be interrelated as follows:
Reference electrode | Electrode potential with respect to SHE (mV) |
---|---|
Standard hydrogen electrode (SHE) | 0 |
Saturated calomel electrode (SCE) | +241 |
Ag/AgCl, 1 M KCl | +236 |
Ag/AgCl, 4 M KCl | +200 |
Ag/AgCl, sat. KCl | +197 |
For example, if one measured 300 mV using a saturated KCl Ag/AgCl reference(ref2) and wanted to refer it to the standard reduction potential measured using a SHE reference electrode (ref1), then 197 mV should be added to the 300 mV to obtain 497 mV, since
it follows that
and therefore
Likewise, if one measured 300 mV using a saturated KCl Ag/AgCl reference (ref2) and wanted to determine the corresponding measurement using an SCE reference (ref1), then given
it follows that
and therefore
Read more about this topic: Reduction Potential
Famous quotes containing the words converting, types and/or reference:
“A way of certifying experience, taking photographs is also a way of refusing itby limiting experience to a search for the photogenic, by converting experience into an image, a souvenir. Travel becomes a strategy for accumulating photographs.”
—Susan Sontag (b. 1933)
“The wider the range of possibilities we offer children, the more intense will be their motivations and the richer their experiences. We must widen the range of topics and goals, the types of situations we offer and their degree of structure, the kinds and combinations of resources and materials, and the possible interactions with things, peers, and adults.”
—Loris Malaguzzi (19201994)
“A sign, or representamen, is something which stands to somebody for something in some respect or capacity. It addresses somebody, that is, creates in the mind of that person an equivalent sign, or perhaps a more developed sign. That sign which it creates I call the interpretant of the first sign. The sign stands for something, its object. It stands for that object, not in all respects, but in reference to a sort of idea, which I have sometimes called the ground of the representamen.”
—Charles Sanders Peirce (18391914)