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During the early development of electrochemistry, researchers used the normal hydrogen electrode as their standard for zero potential. This was convenient because it could actually be constructed by "[immersing] a platinum electrode into a solution of 1 N strong acid and [bubbling] hydrogen gas through the solution at about 1 atm pressure".
Both the oxidation and reduction steps are pH dependent. Figure 1 shows the standard potentials at pH 0 (strongly acidic) as referenced to the normal hydrogen electrode (NHE). 2 half reactions (at pH = 0) Oxidation 2H 2 O → 4H + + 4e − + O 2 E° = +1.23 V vs. NHE Reduction 4H + + 4e − → 2H 2 E° = 0.00 V vs. NHE
Examples of substances that are common reducing agents include hydrogen, Carbon monoxide, the alkali metals, formic acid, [1] oxalic acid, [2] and sulfite compounds. In their pre-reaction states, reducers have extra electrons (that is, they are by themselves reduced) and oxidizers lack electrons (that is, they are by themselves oxidized).
The values below are standard apparent reduction potentials (E°') for electro-biochemical half-reactions measured at 25 °C, 1 atmosphere and a pH of 7 in aqueous solution. [1] [2] The actual physiological potential depends on the ratio of the reduced (Red) and oxidized (Ox) forms according to the Nernst equation and the thermal voltage.
In aqueous solutions, redox potential is a measure of the tendency of the solution to either gain or lose electrons in a reaction. A solution with a higher (more positive) reduction potential than some other molecule will have a tendency to gain electrons from this molecule (i.e. to be reduced by oxidizing this other molecule) and a solution with a lower (more negative) reduction potential ...
As E approaches E s, the current on the surface increases, and when E = E s, the concentration of A equals that of the oxidized/reduced A at the surface ([A] = [A −]). [4] As the molecules on the surface of the working electrode are oxidized/reduced, they move away from the surface and new molecules come into contact with the surface of the ...
When an oxidizer (Ox) accepts a number z of electrons ( e −) to be converted in its reduced form (Red), the half-reaction is expressed as: + The reaction quotient (Q r), also often called the ion activity product (IAP), is the ratio between the chemical activities (a) of the reduced form (the reductant, a Red) and the oxidized form (the oxidant, a Ox).
The data below tabulates standard electrode potentials (E°), in volts relative to the standard hydrogen electrode (SHE), at: Temperature 298.15 K (25.00 °C; 77.00 °F); Effective concentration (activity) 1 mol/L for each aqueous or amalgamated (mercury-alloyed) species; Unit activity for each solvent and pure solid or liquid species; and