The specific ion interaction equations

The summation in Eq.(B.l) extends over all ions k present in solution. Their molality is denoted m, and the specific ion interaction parameters, s(/, k, If), in general depend only slightly on the ionic strength. The concentrations of the ions of the ionic medium are often very much larger than those of the reacting species. Hence, the ionic medium ions will make the main contribution to the value of log y. for the reacting 

Equation (B.l) will allow fairly aecurate estimates of the activity 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. 

The way in which the activity coefficient corrections are performed in this review according to the specific ion interaction theory is illustrated below for a general case of a complex formation reaction. Charges are omitted for brevity. 

Under these conditions, I mx = Wn Substituting the logioY j values in Eq.(B.3) with the corresponding forms of Eq.(B.4) and rearranging leads to  

Equilibria involving H20(l) as a reactant or product require a correction for the activity of water, an . The activity of water in an electrolyte mixture can be calculated as  

The formation constant of M ,L (OH) , , determined in an ionic medium (1 1 salt NX) of the ionic strength /, , is related to the corresponding value at zero 

The summation in Eq. (B.l) extends over all ions k present in solution. Their molality is denoted by / , and the specific ion interaction parameters,, in 

this variety of valnes for Baj does not represent an uncertainty range, but rather indicates that several different sets of Buj and e(j,k,l ) may describe eqnally well the experimental mean activity coefficients of a given electrolyte. The ion interaction coefficients at 25°C listed in Table B-4, Table B-5, Table B-6 and Table B-7 have thns to be nsed with 5a, = 1.5 kg moT.  

For cases where the uncertainties in the epsilon values collected in Table B-4 and Table B-5 are +0.03 kg-mof or greater, Ciavatta [1980CIA] proposed the use of Equation (B.3) 

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The extrapolation procedure used in this review is the specific ion interaction model outlined in Appendix B. The objective of this review is to provide selected data sets at standard conditions, i.e., among others, at infinite dilution for aqueous species. Equilibrium constants determined at different ionic strengths can, according to the specific ion interaction equations, be extrapolated to / = 0 with a linear regression model, yielding as the intercept the desired equilibrium constant at / = 0, and as the slope the stoichiometric sum of the ion interaction coefficients, As. The ion interaction coefficient of the target species can usually be extracted from As and is listed in the corresponding table of Appendix B. 

The correction of log, P (C.17) to = 0 is done using the specific ion interaction equation, cf. TDB-2, which uses molal units ... 

Figure VIII-9 Extrapolation to / = 0 of experimental data for the formation of ThCr using the specific ion interaction equation. The data refer to mixed perchlorate/chloride media and are taken from [1950DAY/STO], [1951ZEB/ALT], [1952WAG/STO] and [1975PAT/RAM],...

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