Oxidation — Reduction Electrodes

The general equation for the reaction at an oxidation-reduction electrode may be written ... 

The complete reaction may be regarded as composed of two oxidation-reduction electrodes, a Ox, a Red, and frOx , b Red, combined together into a cell at equilibrium, the potentials of both electrodes are the same ... 

Oxidation-reduction electrodes. An inert metal (usually Pt, Au, or Hg) is immersed in a solution of two soluble oxidation forms of a substance. Equilibrium is established through electrons, whose concentration in solution is only hypothetical and whose electrochemical potential in solution is expressed in terms of the appropriate combination of the electrochemical potentials of the reduced and oxidized forms, which then correspond to a given energy level of the electrons in solution (cf. page 151). This type of electrode differs from electrodes of the first kind only in that both oxidation states can be present in variable concentrations, while, in electrodes of the first kind, one of the oxidation states is the electrode material (cf. Eqs 3.1.19 and 3.1.21). 

Oxidation-reduction electrodes, abbreviated to redox electrodes, consist of an inert metal (Pt, Au, Hg) immersed in a solution containing two forms... 

Oxidation-reduction electrodes These electrodes consist of an inert metal in a solution containing ions that can undergo oxidation-reduction reactions. An example is a platinum wire immersed in a solution containing Fe2+ and Fe3+ ions. Transfer of electrons into the solution is accompanied by reduction of some Fe3+ to Fe2+. 

The confusion in theories is considerable, and is not much enlightened by the great variety of mathematical treatment, much of which, as seems all too frequent nowadays, appears to contain conveniently adjustable constants. It is to be hoped, however, that clear discussion on the lines of Gurney s treatment of the reversible electrode mentioned in 4, is not far distant. At present, it certainly seems as if the rate of recombination of adsorbed hydrogen atoms is important, perhaps of predominating importance. If the transfer of electrons from metals to ions in solution were intrinsically a slow process, the oxidation-reduction electrodes would not be reversible. 

Another type of reversible electrode involves an unattackable metal, such as gold or platinum, immersed in a solution containing an appropriate oxidized and reduced form of an oxidation-reduction system, e.g., Sn++++ and Sn++, or Fe(CN)6 and Fe(CN)6 the metal merely acts as a conductor for making electrical contact, just as in the case of a gas electrode. The reaction at an oxidation-reduction electrode of this kind is either oxidation of the reduced state or reduction of the oxidized state, e.g.,... 

Determination of Standard Oxidation-Reduction Potentials.—In principle, the determination of the standard potential of an oxidation-reduction system involves setting up electrodes containing the oxidized and reduced states at known activities and measuring the potential B by combination with a suitable reference electrode insertion of the value of B in the appropriate form of equation (3) then permits B to be calculated. The inert metal employed in the oxidation-reduction electrode is frequently of smooth platinum, clthough platinized platinum, mercury and particularly gold are often used. 

The positive electrode may also be regarded as a simple oxidation-reduction electrode involving the plumbous-plumbic system thus... 

All electrodes depend on oxidation and reduction, but the term oxidation-reduction electrode, or redox electrode, is usually reserved for the case in which a species exists in solution in two oxidation stages. This electrode is denoted M(s) Ox, Red, where M is an inert metal (usually platinum) serving as an electron carrier and making electrical contact with the solution. The half-cell equilibrium can either be simple (e.g., Fe + + e = Fe +) or be affected by other... 

Hi) The Oxidation-Reduction Electrode is one in which the electrode itself is inert e.g, pure platinum) and the solution contains ions of variable charge, say iron(II) and ir(m(III) ions. Supply of electrons then causes reduction of the higher ion to the lower, Fe e -> Fe, and removal of electrons causes oxidation of the lower ion to the higher, Fe — e -> Fe +. 

The Standard Potential of the Mercurous-Mercuric Electrode. A method for obtaining standard potentials of oxidation-reduction electrodes which utilizes the best procedure so far developed in this field is the one that was used by Fopoff and associates. The method may be illustrated by the determination of the standard potential of the mercurous-mercuric electrode. The type of cell used by Popoff, Riddick, Worth and Ough1 was... 

Some standard oxidation/reduction electrode potentials of fundamental technetium... 

Any electrode involves oxidation and reduction in its operation, but these electrodes have had that superfluous phrase attached to them. An oxidation-reduction electrode has an inert metal collector, usually platinum, immersed in a solution that contains two soluble... 

Optical properties of gold nanorod arrays have been studied and were found to be dominated by surface plasmon modes superimposed on interference effects [99]. The formation of a surface complex composed of molecules (e.g. pyridine or pyr-azine) strongly bound to silver formed during oxidation-reduction electrode potential cycles is evident in ER spectra shown in Fig. 5.18. They show pronounced absorptions not found with the respective molecules in solution. 

The basic electrode is an oxidation-reduction electrode operating under equilibrium conditions between electrons in a noble metal, hydrogen ions in solution, and dissolved molecular hydrogen. The activity of dissolved hydrogen, an+, is taken as the independent variable and is fixed by maintain-... 

The potential of a reversible oxidation-reduction electrode measured with respect to a reference electrode, corrected to the hydrogen electrode, in a given electrolyte. 

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