Estimation of ion interaction coefficients

1 Estimation from mean activity coefficient data Example B.1  

The ion interaction coefficient e(H, CF) can be obtained from published values of 

By plotting (log, + D) versus mua a straight line with the slope 

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From Tables 6.3 and 6.4 it seems that the size and charge correlations can be extended to complex ions. This observation is very important because it indicates a possibility to estimate the ion interaction coefficients for complexes by using such correlations. It is, of course, always preferable to use experimental ion interaction coefficient data. However, the efforts needed to obtain these data for complexes will be so great that it is unlikely that they will be available for more than a few complex species. It is even less likely that one will have data for the Pitzer parameters for these species. Hence, the specific ion interaction approach may have a practical advantage over the inherently more precise Pitzer approach. 

It should be noted that ion interaction coefficients tabulated in Tables 6.3-6.5 may also involve ion pairing effects, as described in section 6.3. In direct comparisons of ion interaction coefficients, or when estimates are made by analogy, this aspect must be taken into account. 

The specific ion interaction approach is simple to use and gives a fairly good estimate of activity factors. By using size/charge correlations, it seems possible to estimate unknown ion interaction coefficients. The specific ion interaction model has therefore been adopted as a standard procedure in the NEA Thermochemical Data Base review for the extrapolation and correction of equilibrium data to the infinite dilution standard state. For more details on methods for calculating activity coefficients and the ionic medium/ ionic strength dependence of equilibrium constants, the reader is referred to Ref. 40, Chapter IX. 

B.3. In direct comparisons of ion interaction coefficients, or when estimates are made by analogy, this aspect must be taken into account. 

In a few cases we have used the equilibrium constants for minor species to estimate their ionic strength dependence and to show the charge and size systematics of ion interaction coefficients. 

Zhang and Mohammed (1998) estimated an ion interaction coefficient for e(Ni20H, C104 ) = 0.59 0.16 kg mol from which Gamsjager et al. (2005) determined a value of 0.2)kgmol (the standard specific ion... 

Estimation from Mean Activity Coefficient Data Example 1 The ion interaction coefficient e jj+ can be obtained from published values of 7 hci vs. mnci-... 

Eq. (B.l) will allow fairly accurate estimates of the aetivity coefficients in mixtures of electrolytes if the ion interaction coefficients are known. Ion interaction coefficients for simple ions can be obtained from tabulated data of mean activity coefficients of strong electrolytes or from the corresponding osmotic coefficients. Ion interaction coefficients for complexes can either be estimated from the charge and size of the ion or determined experimentally from the variation of the equilibrium constant with the ionic strength. 

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