Concentration effects, anion

The distribution of highly extractable solutes such as and Pu between the aqueous and organic phases is strongly dependent upon the nitrate anion concentration in the aqueous phase. This salting effect permits extraction or reextraction (stripping) of the solute by controlling the nitric acid concentration in the aqueous phase. The distribution coefficient, D, of the solute is expressed as... 

Of course, these concentration effects will be highly dependent on the nature of the substrate dissolved in the ionic liquid, as well as on the nature of the ionic liquid s cation and anion. Given the enormous opportunity to vary these last two, it becomes clear that a detailed understanding of the role of the ionic liquid in reaction mixtures is far from complete. Clearly, this limited understanding is currently restricting our opportunities to benefit from the full potential of an ionic liquid solvent in a given synthetic application. 

Fig. 2.2 Effect of increasing anion concentration on corrosion rate of mild steel in sodium salt...

The relative importance of these functions also depends to a considerable extent on the solution conditions. Under favourable conditions of pH, oxidising power and aggressive anion concentration in the solution, Function 1 is probably effective in preventing film breakdown. Under unfavourable conditions for inhibition, localised breakdown will occur at weak points in the oxide film, and Functions 2 and 3 become important in repairing the oxide film. 

Effects of acid strength and anion concentration have been studied as well as the effect of monodentate amines.564,565 Phosphines, in particular dppp, have been used as favorable ligands,566,567 but it has been shown that dppp is oxidized by nitrobenzene under the prevailing conditions.568 Giant clusters and heteropolyanions have been used.569,570 The role of nitroso... 

In previous sections, numerous examples of anion activation by cationic micelles and polysoaps were presented. The extent of rate augmentation— 102—lO -fold—cannot be rationalized in terms of concentration effects alone. We believe that these observations are explained most reasonably by the concept of the hydrophobic ion pair (Kunitake et al., 1976a). According to this concept, anionic reagents are activated probably due to desolvation when they form ion pairs with an ammonium moiety in a hydrophobic microenvironment. The activation of anionic species in the cationic micellar phase... 

In these solutions pH is more strongly correlated with total anion concentration than with ionic strength. Thus 1 M Na2S04 and 1 M NaCl have about the same effect on the pH of a solution at a given fraction neutralization. Figure 2 shows pH at 50% neutralization as a function of anion concentration in the solutions which are primarily citrate, Na2S04, or NaCl, as well as in mixed solutions. 

The effect of solution anionic concentration is probably related to effects on activity coefficients and ion pair formation of more highly charged buffer species. In more concentrated solutions, the activity of the highly charged species is reduced by both ionic strength and ion pair formation. The effect on less charged, acidic species is less. Therefore, as solutions become more concentrated, the activity of basic species is reduced relative to that of acidic species, and at a given fraction... 

The effect of fraction neutralization on pH is illustrated in figure 3 for a solution of constant anionic concentration. 

Series 8 in combination with earlier series was intended to provide data on the effects of total anion concentration. The results are internally consistant with the correlation, having a standard deviation of about 15% around the mean error. However the measured values of PSO2 were about 40% lower than the general correlation. An SO2 analyzer, rather than iodine titration, was used to determine SO2 gas concentration from the saturator. The analyzer was calibrated with dry SO2/N2 span gas. In later experiments it was shown that humid gas gives a lower analyzer response. With constant fraction neutralization increased anionic concentration increases PSO2 because pH decreases faster than effective bisulfite activity. 

The dependence on fraction neutralization and total anion concentration should reflect the extent to which the bisulfite activity is not proportional to total dissolved SO2. As expected, the dependence on f is quite small, since dissolved SO2 is present primarily as bisulfite at pH 3.5 to 5.0. The effect of anion concentration is in the direction expected since bisulfite activity would be reduced by ion pairing in more concentrated solutions. 

The increase in the anion concentration results in higher values of Cj at the maximum and in the shift of the maximum toward the zero charge density. The shift of the peak with increasing concentration is caused by the screening effect of the anions, accumulated in the diffuse layer and linked to the positive ends of the solvent dipoles. However, the changes in the shape of the C, vs. plots are greater on the negative than on the... 

Base cations are mobilized by weathering and cation exchange reactions that neutralize acids in the watershed. They respond therefore indirectly to changes in sulphate and nitrate concentrations. In fact, if acid anion concentrations (mainly sulphate) decrease, base cations are also expected to decrease. However, in the last few years an increase of the occurrence of alkaline rain episodes (probably due to climatic effects) has been observed and it is likely that calcareous Saharan dust, rich in base cations, is responsible for it [27]. Accelerated weathering, resulting from recent climate warming may also contribute to higher base cation concentrations [28]. 

Since movement within the solvation shell in these complexes is relatively sluggish, it is postulated that a complex remains activated only long enough to react with its immediate environment, the inner solvation shell. In the reaction with anionic species, a situation can be reached in which nearly all of the substrate is in the form of the maximum ion aggregate. Any increase in the anion concentration in the bulk solvent will not change the immediate environment of nearly all the substrate and, therefore, will not effect the reaction rate. In this way a limiting rate can be independent of the concentration of added anionic reagent, irrespective of the actual mechanism of the actual act of substitution. 

Such a mechanism was postulated by R. Plane and H. Taube (5) in discussing the Cr(H20)e+3—H20 exchange which was found to be linearly dependent on anion concentration. With this linear dependence no distinction is possible between an association mechanism, in which the associated anion has a generally labilizing effect on the complex, and the abstraction mechanism in which the anion acts specifically to remove a particular water molecule. W. Plumb and G. Harris (6) have found that the Rh(H20)6+3-H20 exchange is also dependent on (C Of ) over a wide concentration range. In both of the above studies the ionic strength varied directly with the anion concentration and the behaviour has been ascribed to this (6). 

The solvation numbers of ions such as Mg2+, Al3+, and Be2+ may be determined by low temperature PMR techniques as mentioned earlier. The solvation number for small spherical ions may be determined in certain circumstances using a titration technique suggested by Van Geet (15). It is based on the competition by water for the solvation sphere of sodium ions in tetrahydrofuran (THF) measured by Na shifts. The salt must contain a large anion, which is assumed to be unhydrated during the titration otherwise a sum of hydration numbers would be determined. The assumptions made by Van Geet are basically those of the present treatment. His apparent constant is for the reverse of the equilibrium of Equation 21 and can be identified as l/K[P]p, where [P]f is the free THF concentration, effectively constant in the early stages of the titration. 

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