Ground ionic concentrations

After the preceding considerations, it is quite understandable that the total ionic concentration of a solution is of major importance. Depending on its value, it may govern its thermodynamic behavior. Lewis was the first to note, on purely experimental grounds, that it is the ionic strength of a solution that is important in this respect. The ionic strength of a solution is defined as... 

The formation of a detectable quantity of weak CT complexes usually requires a large excess of one component, or high concentrations of both components. Such a situation may lead to mechanistic complications. Thus, 1 2 complexes may form in the ground state [54], or the photogenerated ion pairs may be rapidly (subnanosecond or nanosecond time scale) intercepted to form triplexes [55] or ionic dimers [56]. It may be expected that the chemical behavior of these aggregates will crudely resemble the reactivity of normal ion pairs. 

From several points of view (for example, in battery technology), it is extremely important to have solutions of maximum specific conductivity. Basically, the specific conductivity increases proportionally to the concentration of ions. On this simplistic ground, it would seem important to have as high a concentration as possible up to the solubility limits. However (see the work of Haymet described in Chapter 3), increasing concentration leads to an inaease of ionic association which decreases the concentration of conducting entities. Also, as... 

Much spectroscopic and theoretical work has concentrated on the conformational dependence of ground-, excited-, and ionic-state energies. Parametrized computational studies have treated the ground- and excited-state energies of oligomers (33-45) and the bands of infinite polymers (46-47). Until now, few ab initio studies have appeared on the electronic structure of any system larger than disilane (48-57). 

A frequent complication is that several simultaneous equilibria must be considered (Section 3-1). Our objective is to simplify mathematical operations by suitable approximations, without loss of chemical precision. An experienced chemist with sound chemical instinct usually can handle several solution equilibria correctly. Frequently, the greatest uncertainty in equilibrium calculations is imposed not so much by the necessity to approximate as by the existence of equilibria that are unsuspected or for which quantitative data for equilibrium constants are not available. Many calculations can be based on concentrations rather than activities, a procedure justifiable on the practical grounds that values of equilibrium constants are obtained by determining equilibrium concentrations at finite ionic strengths and that extrapolated values at zero ionic strength are unavailable. Often the thermodynamic values based on activities may be less useful than the practical values determined under conditions comparable to those under which the values are used. Similarly, thermodynamically significant standard electrode potentials may be of less immediate value than formal potentials measured under actual conditions. 

Nitsche H., Muller A., Standifer E. M., Deinhammer R. S., Becraft K., Prussin T., and Gatti R. C. (1992) Dependence of actinide solubility and speciation on carbonate concentration and ionic strength in ground water. Radiochim. Acta 58/59, 27-32. 

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