. Biophysics: concepts and mechanisms. Biophysics. REDOX SYSTEMS; ELECTRON TRANSFER PROCESSES 183 that too much variation could cause a normally proceeding reaction actually to go backwards! A special application of the Nernst Equation is discussed under concen- tration cells. + + pH = 0 pH=7 Figure 7-6. £m7's (center vertical line), and Their Relation to the Corresponding P's. (See text and Table 7-4.) Balky Redox Reactions There are three tricks provided by nature to promote electron exchange in oxidation-reduction reactions. The first is catalysis: providing a surface or a
. Biophysics: concepts and mechanisms. Biophysics. REDOX SYSTEMS; ELECTRON TRANSFER PROCESSES 183 that too much variation could cause a normally proceeding reaction actually to go backwards! A special application of the Nernst Equation is discussed under concen- tration cells. + + pH = 0 pH=7 Figure 7-6. £m7's (center vertical line), and Their Relation to the Corresponding P's. (See text and Table 7-4.) Balky Redox Reactions There are three tricks provided by nature to promote electron exchange in oxidation-reduction reactions. The first is catalysis: providing a surface or a site on which the exchange can rapidly take place. For example, electrons exchange immeasurably slowly between H2 and H+ in solution, but if a sur- face such as finely divided platinum metal is added, electron exchange is rapid, and the potential readily manifested. The second trick is the use of an indicator redox system. If one wishes to know the redox potential of a solution in which the electron transfer is slow or sluggish, one can add a very small amount of an entirely foreign redox system, which exchanges electrons rapidly with the system of interest, and which is either itself highly colored or exchanges rapidly at a metal elec- trode. In the first case the depth of color of the resulting solution can be related to the redox potential; and in the second case the potential can be read directly against a reference electrode. Methylene blue, a colored redox dye, is one of a class of dyes commonly used for this purpose, while the addi- tion of a small amount of potassium iodide often will permit direct measure- ment of the redox potential of the solution against some suitable reference. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Casey, Edmund Jeremiah, 1924-. New York, Reinhold Pub. Corp
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