Electrolyte asymmetry

To conclude this section let us note that already, with this very simple model, we find a variety of behaviors. There is a clear effect of the asymmetry of the ions. We have obtained a simple description of the role of the major constituents of the phenomena—coulombic interaction, ideal entropy, and specific interaction. In the Lie group invariant (78) Coulombic attraction leads to the term -cr /2. Ideal entropy yields a contribution proportional to the kinetic pressure 2 g +g ) and the specific part yields a contribution which retains the bilinear form a g +a g g + a g. At high charge densities the asymptotic behavior is determined by the opposition of the coulombic and specific non-coulombic contributions. At low charge densities the entropic contribution is important and, in the case of a totally symmetric electrolyte, the effect of the specific non-coulombic interaction is cancelled so that the behavior of the system is determined by coulombic and entropic contributions. 

It has become fairly common to adopt the manufacture of combinations of internal reference electrode and its inner electrolyte such that the (inner) potential at the glass electrode lead matches the (outer) potential at the external reference electrode if the glass electrode has been placed in an aqueous solution of pH 7. In fact, each pH glass electrode (single or combined) has its own iso-pH value or isotherm intersection point ideally it equals 0 mV at pH 7 0.5 according to a DIN standard, as is shown in Fig. 2.11 the asymmetry potential can be easily eliminated by calibration with a pH 7.00 0.02 (at 25° C) buffer solution. 

As pointed out in Section II.3.ii, the key principle of the galvanic cells relies on chemical asymmetry and a zero cr on in the electrolyte rendering possible the fact that there can be an electrochemical potential gradient, i.e., a nonzero cell voltage without having a current. 

The behavior of surface tension at high ionic strength also can be understood on the basis of changes in ion hydration changes between bulk and interface. The tendency of the structure-breaking ions to accumulate at the surface can lead to a positive surface adsorption. However, if the cations cannot approach the interface, the asymmetry of the ion distributions generates a potential, which repels the anions from the interface, and the total adsorption becomes negative. Consequently, the surface tension increases with electrolyte concentration this occurs for simple salts (NaCl, KC1). If the cations can approach the interface, the accumulation of anions in the vicinity of the interface is also followed by an accumulation of cations,... 

The standard theory of colloidal interactions is that of DLYO [29, 30]. They used the primitive model of the electrolyte. Because of the asymmetry in the DH theory, they applied the DH/PB theory to a fluid of charged point ions in a slit to width L. Restricting our attention to the linearized case, the slit profile is... 

Figure 3.10 illustrates the same trends in terms of capacitances. In this example the asymmetry of the electrolyte has been varied at fixed concentration. In this plot the trends are more pronounced than in fig. 3.9. The new feature is that the capacity minimum no longer coincides with the zero point of the diffuse layer potential, but is shifted in the direction where the multivalent ion is the co-ion. (In fig. 3.9 the same can be seild of the position of the minimum slope.) The value y (min) where the capacitance minimum is located can be obtained by differentiating [3.5.34] with respect to y leading to the condition... 

This method was applied to the asymmetric reduction of ketones [440 44] and imines [439,445]. Maximum asymmetric yields reported for the former and the latter are 20% [441] and 8.95% [445], respectively. A higher asymmetric yield (20.6%) was obtained in the hydrodimerization of a ketone [444]. It is a problem that lower asymmetric yields are obtained using much larger amounts of asymmetry inducers, which must play the role of supporting electrolyte. 

In the series Ba2+, Cu2+, Y3+ the cation size increases. These cations do not create the ion pairs with anion NO3 and the dependence of es on the ion strength for nitrate salts is in agrement with our previous conclusions about the dependence of the solvent dielectric constant on the ion concentration with change of 5. For the formate salts, these cations create ion pairs with anions CHOO- due to hydrogen bonds between anion and water molecules from the hydration shell of cation thus, the degree of association increases with the decrease of ion size. As a result, we obtaine the concentration dependence for es that is opposite to nitrate salts. Since the considered theory is elaborated for the symmetrical electrolytes and experimental data concern the asymmetri-... 

Spherical micelles or globular proteins in solution can be considered as an asymmetric electrolyte solution where the ionic species grossly differ in charge and size. Taking into account these asymmetries, an extension of WOZ equa-... 

Consider, for example, the terms which specify charge. As recorded earlier, measured values for pzc vary and are below the theoretical value largely because of the presence of adsorbed carbonate. In this model, the observed values for the pzc are described by the choice of values for Kh and Kqh- Analogous terms are used in other models. The values so obtained are not fundamental properties of the surface but artifacts of the preparation and treatment of the oxide. Furthermore, adding acid to such a surface will displace some carbonate and thus induce an asymmetry in the titration curves. These asymmetries are described by differences in the K terms for the electrolyte cations and anions. Lumsdon and Evans [52] have recently shown that different values for model parameters are needed for C02 free goethite. 

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