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A standard half-cell consists of a metal electrode in an aqueous solution where the concentration of the metal ions is 1 molar (1 mol/L) at 298 kelvins (25 °C). [1] In the case of the standard hydrogen electrode (SHE), a platinum electrode is used and is immersed in an acidic solution where the concentration of hydrogen ions is 1M, with ...
Scheme of the standard hydrogen electrode. The scheme of the standard hydrogen electrode: platinized platinum electrode; hydrogen gas; solution of the acid with activity of H + = 1 mol dm −3; hydroseal for preventing oxygen interference; reservoir through which the second half-element of the galvanic cell should be attached.
The standard hydrogen electrode (SHE), with [ H +] = 1 M works thus at a pH = 0. At pH = 7, when [ H +] = 10 −7 M, the reduction potential of H + differs from zero because it depends on pH. Solving the Nernst equation for the half-reaction of reduction of two protons into hydrogen gas gives: 2 H + + 2 e − ⇌ H 2
The reference half cell consists of a redox standard of known potential. The standard hydrogen electrode (SHE) is the reference from which all standard redox potentials are determined, and has been assigned an arbitrary half cell potential of 0.0 V. However, it is fragile and impractical for routine laboratory use.
A reference electrode is an electrode that has a stable and well-known electrode potential. The overall chemical reaction taking place in a cell is made up of two independent half-reactions , which describe chemical changes at the two electrodes.
The indicator electrode forms an electrochemical half-cell with the interested ions in the test solution. The reference electrode forms the other half-cell. The overall electric potential is calculated as = +. E sol is the potential drop over the test solution between the two electrodes. E cell is recorded at intervals as the titrant is added ...
The cell potential can be predicted through the use of electrode potentials (the voltages of each half-cell). These half-cell potentials are defined relative to the assignment of 0 volts to the standard hydrogen electrode (SHE). (See table of standard electrode potentials). The difference in voltage between electrode potentials gives a ...
For example, the absolute half-cell entropy has been defined as the entropy of the absolute half-cell process defined above. [4] An alternative definition of the absolute half-cell entropy has recently been published by Fang et al. [5] who define it as the entropy of the following reaction (using the hydrogen electrode as an example):