Conjugate redox couple

Standard Reduction Potentials of Some Conjugate Redox Couples " ... 

Figure 8.17 Cyclic voltammograms (at 1 mVs" ) of two-electrode cells operating with activated carbons AAC 1 or AAC 2 in iodide/vanadium conjugated redox couples as electrolyte solutions [112].

Again, we have conjugate pairs, this time conjugate redox couples, e.g. the pair... 

Concept The rates of long-range electron transfer (ET) and excitation energy transfer (EET) processes between a pair of chromo-phores (redox couple) may be strongly facilitated by the presence of an intervening non-conjugated medium, such as saturated hydrocarbon bridges, solvent molecules and n-stacks, e.g.,... 

The thermodynamic relations of any particular redox couple can therefore be calcnlated from the valnes for the reaction between the couple of interest and the hydrogen ion—hydrogen gas couple. Thus for the reduction of oxidant Ox to its conjugate reductant Red, we have ... 

Although all potentiometric measurements (except those involving membrane electrodes) ultimately are based on a redox couple, the method can be applied to oxidation-reduction processes, acid-base processes, precipitation processes, and metal ion complexation processes. Measurements that involve a component of a redox couple require that either the oxidized or reduced conjugate of the species to be measured be maintained at a constant and known activity at the electrode. If the goal is to measure the activity of silver ion in a solution, then a silver wire coupled to the appropriate reference electrodes makes an ideal potentiometric system. Likewise, if the goal is to monitor iron(UI) concentrations with a platinum electrode, a known concentration of... 

Note that we can consider the potential of a solutionin the same way as we do the pH of a solution. The potential is defined by the presence of an oxidized and a reduced form of a redox couple, just as the pH is defined by the presence of an acid and its conjugated base. The potential is there regardless of whether we measure it or not, and therefore does not rely on contact with any electrodes. The potential of a solution should be no more mysterious than its pH, except that we happen to have a sense for acidity in our taste buds, but not one for potential. Still, we can imagine the pH of soil or blood without tasting it, and it should be no different for its potential. Of course, any direct measurement of the potential of a solution requires electrodes, but the potential can also be calculated from the concentrations of the redox partners when these are otherwise known or measurable, just as the pH can be calculated from, say, the spectrum of a solution containing pH-sensitive indicator dyes. 

The simultaneous presence of the oxidized and reduced form of a redox couple can stabilize the redox potential of a solution, just as the presence of an acid and its conjugate base can stabilize the pH. The formalism (R. de Levie, /. Chem. Educ. 76 (1999) 574) is quite similar to that of section 4.7, except that there are no terms for the oxidation or reduction of the solvent, because these are typically non-equilibrium processes which, moreover, are insignificant in the usual range of potentials considered. By analogy to (4.7 -1) we write, for the redox buffer strength B of a one-electron redox couple Ox+ e Red, such as Fe3++ e-—Fe2+orCe4++ e Ce3+,... 

Here, H O plays the role of base but, combining with H, forms an acid - hydroxonium H O. Acids (donors of H ) and bases (acceptors of H ) in such elementary reactions are called conjugated couples, which exchange proton (analogue of redox-couples). 

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