OXIDATION REDUCTION EQUILIBRIA

Oxidation-reduction equilibria play an important role in water technology particularly from the viewpoint of the calculation of a relative representation of individual oxidation degrees of the element in the system. Oxidation-reduction potentials are used in theoretical studies for checking the iron and manganese removal, water chlorination, in the study of the 

The value of the oxidation-reduction potential can be calculated by substituting the activities of reacting substances into the Nernst-Peters equation 

The measurement and quantitative evaluation of redox potentials in waters is difficult. It is of great importance in the systems with known composition. For the measurement, electrometric methods are used. At the same time, pH, temperature and oxygen concentration are determined. A saturated calomel electrode serves as a reference and a platinum one as the measuring electrode. Oxidation-reduction equilibria are described in detail elsewhere [6, 7]. 

Physical Chemistry, 4th ed. Prentice-Hall, Englewood Cliffs 1972. 

Eyring, H., Lin, S.H. and Lin, S.M. Basic Chemical Kinetics. J. Wiley-Interscience, New York 1980. 

In redox reactions, to an extent greater than found in other types of reactions, systems which are not reversible or are not in equilibrium are encountered. In such systems, although the predicted potential differences based on equilibrium behavior will not agree with observed values, such calculations are nevertheless useful in describing the relative strengths of oxidants and reductants. 

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Analytical methods based upon oxidation/reduction reactions include oxidation/reduction titrimetry, potentiometry, coulometry, electrogravimetry and voltammetry. Faradaic oxidation/reduction equilibria are conveniently studied by measuring the potentials of electrochemical cells in which the two half-reactions making up the equilibrium are participants. Electrochemical cells, which are galvanic or electrolytic, reversible or irreversible, consist of two conductors called electrodes, each of which is immersed in an electrolyte solution. In most of the cells, the two electrodes are different and must be separated (by a salt bridge) to avoid direct reaction between the reactants. 

Goldaman, J.A., Oxidation—Reduction Equilibria and Titration Curves , In Treatise on Analytical Chemistry, ed. by I.M. Kolthoff and PJ. Elving, 2nd ed., Vol. 3, New York, Interscience Publications, John Wiley Sons Inc., 1983. 

Oxidation-reduction equilibria exhibit a conceptual analogy to acid-base equilibria. Similar to the approach of acids and bases acting as proton donors and proton acceptors, reducing and oxidization agents are electron donors and electron acceptors, respectively (recall Sect. 2.2.2). The redox reaction between m moles of an oxidant A... 

Clark, W. M. 1934. The acid-base and oxidation-reduction equilibria of milk. In Fundamentals of Dairy Science, 2nd ed. Assoc, of Rogers Reinhold Pulishing Corp, New York, pp. 137-154. 

The optical absorption spectra of Pu ions in aqueous solution show sharp bands in the wavelength region 400—1100 nm (Fig. 4). The maxima of some of these bands can be used to determine the concentration of Pu ions in each oxidation state (III—VI), thus quantitative determinations of oxidation—reduction equilibria and kinetics are possible. A comprehensive summary of kinetic data of oxidation—reduction reactions is available (101) as are the reduction kinetics of Pu7+ (aq) (84). 

In oxidation-reduction equilibria, the common reagent is the electron e", and matters are simplified considerably if one treats the electron like any other reagent, H+, Ag+, Cl", etc. (Note that neither of these exists free and unhydrated in aqueous solutions). Clark has suggested (6) using e, and J0rgensen (8) has suggested the definition ... 

When dte oxidation-reduction equilibria in equation (6a) ate included, the thermal activation of elec-tron-transfn oxidation in equation (3b) follows a course that is akin to charge-transfn activation in equation (5). In both, the A cotiq>lex [RH,A] is the important precursor which is directly converted into the critical contact ion pair [RH, A ]. Such an involvonent of reactive intermediates in common does widen the scqte of electron-transfer oxidations to include both thermal and photochemical pro-... 

Oxidation-Reduction Equilibria.—When two reversible oxidation-reduction systems are mixed a definite equilibrium is attained which is... 

We can study oxidation/reduction equilibria conveniently by measuring the potentials of electrochemical cells in which the two half-reactions making up the equilibrium are participants. For this reason, we must consider some characteristics of electrochemical cells. 

Many of the sulfur oxoacids and their salts are connected by oxidation-reduction equilibria some of the more important standard reduction potentials are summarized in Table 15.19 and displayed in graphic form as a volt-equivalent diagram (p. 435) in Fig. 15.28. By use of the couples in Table 15.19 data for many other oxidation-reduction equilibria can readily be calculated. (Indeed, it is an instructive exercise to check the derivation of the numerical data... 

The concept of electron activity is used in the description of oxidation-reduction equilibria and especially in the solution of problems that involve both redox and other equilibria such as acid-base, complexation, and so forth. In addition, this concept provides a useful basis for the graphical representation of complicated redox equilibria. The approach is extremely useful when working with redox equilibria in natural waters. 

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