Side reaction coefficient

Side reactions (and side reaction coefficients) — Reactions that accompany a main reaction or electrochemical system. Example When the redox system Fe(II)/Fe(III) in aqueous solutions is studied, the following redox equilibrium is the main reaction Fe3+ + e" Fe2+. Since the standard potential of that system relates to the two aqua complexes [Fe(Fl20)6]3+ and [Fe(H20)6]2+, a number of possible side reactions (in fact equilibria ) have to be taken into account the Fe(III) hexaqua complex is prone to acid-base reactions according to [Fe(H20)6]3+ + H20 [Fe(H20)50H]2+ + H30+)etc.)... 

The side reactions can considerably change the concentration of the free metal ion and the free organic ligand. To account for their effect on the main equilibrium, the side-reaction coefficients qcm, Kl and Mml as defined by Ringbom et al. need to be introduced into the stability constant (106). The side reaction coefficients are, of course, functions of the equilibrium constants of the side reactions if [M ] is the conditional concentration of M (all the forms of M not complexed with L), [L ] is the conditional concentration of L (all the forms of L not coordinated by M) and [ML ] is the conditional concentration of ML (the metal complex present in all the forms, even as mixed complexes, then the mathematical relationships to describe m, ocl and aML are ... 

OH ). With respect to complexation by OH, the inorganic side-reaction coefficients of the strongly hydrolyzed metals range from for Al + to... 

Other important inorganic species are the chloride and carbonate complexes. Chloride complexes are important in the inorganic speciation of Ag" ", Cd, and Hg. Unlike the strongly hydrolyzed metals, chloride dominated metals are only moderately affected by temperature and pH. Of this group, Hg " " is complexed by chloride to the greatest extent. The side reaction coefficient of Hg with respect to chloride is at 5°C. Carbonate complexes... 

They were introduced in 1941 by a Swede, Ido Leden, as the ratio of total molal (or molar) concentration of any basis component to the content of its dissociated form. This coefficient serves a measure of the effect of secondary components and is considered the side reaction coefficient. It is also often called alpha-coefficient or for a case of reactions of complex compounds formation, complexation function. In the presence of secondary components s > 1, in their absence s.= 1. This coefficient substantially simplifies interrelation between the conditional and concentration equilibrium constants... 

The concept of side reaction coefficients, introduced by A. Ringbom, is useful in describing the effect of pH on various equilibria. These coefficients combine the total (analytical) concentration, [X ], of the species of interest, with the concentration of its form [X], which luidergoes reaction. For example, for eth-ylenediaminetetraacetic acid (EDTA) the reacted form is the EDTA" anion, but the total concentration also includes all protonated forms. Thus, the side reaction coefficient, o edta(H) > is given by... 

The pH value influences the solubility of precipitates of hydroxides of metals, for which the coefficient a is >1. Using the concept of side reaction coefficients the conditional solubility products, fC o, can be calculated ... 

Figure 3 Dependence of side-reaction coefficients, as log a, on pH for some bases (EDTA, anion of ethyienediaminotetraacetic acid NTA, anion of nitriiotriacetic acid).

For various common ligands used in analytical chemistry, such side reaction coefficients can be presented graphically (Figure 3). 

The side-reaction coefficient of the indicator ion, i.e., the ratio of the free determinand to all its chemical forms, should be constant. 

Besides E and E the so-called formal potentials (E, and Ef) are frequently used [5, 7]. The purpose of defining formal potentials is to have cmiditional constant that takes into account activity coefficients and side reaction coefficients (chemical equilibria of the redox species), since in many cases it is impossible to calculate the resulting deviations because neither the thermodynamic equilibrium constants are known, nor it is possible to calculate the activity coefficients. Therefore, the potential of the cell reaction and the potential of the electrode reaction are expressed in terms of concentrations ... 

Side reactions (and side reaction coefficients) — Reactions that accompany a main reaction or electrochemical system. Example When the redox system Fe(II)/Fe(III) in aqueous solutions is studied, the following redox... 

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