Selection of Stability and Solubility Constants

In these equations, and 3 are constants, X is the parameter being determined, 

Stability and solubility constants were largely selected based on their consistency across a number of studies. The consistency may relate to where multiple data are available for a single set of conditions or one or more data are available for multiple conditions (i.e. either temperature or ionic strength). The temperature dependence of stability or solubility constants is based around the relationship of the constants with the inverse of absolute temperature assuming a constant heat capacity (whether zero or non-zero) and that for ionic strength is dependent on the relationship of the constants with respect to the specific ion interaction theory (standard or extended). The consistency is related to the agreement between the measured stability or solubility constants with respect to their uncertainties and the equation used to explain the temperature or ionic strength effects. 

In a small number of cases, a stability or solubility constant is available for a particular species or phase from a single study only. In these cases, the constant will be accepted if it can be related to other similar data (e.g. a lanthanide metal ion being compared with the data of other lanthanide metal ions). If the single study relates to measurement of the stability or solubility constant at a fixed ionic strength (and no other data are available at other ionic strengths), it can be corrected to zero ionic strength if similar data are available for like metal ions where 

Data selected in this review have been assigned uncertainties at a 95% confidence level. The selected data can then be utilised further to determine relevant stability or solubility constants (often, the uncertainties derived for these data are quoted to two significant figures) which, in turn, are used to derive thermodynamic data, all of which will also have uncertainties at a 95% confidence level. In some cases, an uncertainty for the 95% confidence level has been assigned within this review by judgement. Such assignments are, by definition, subjective. 

The appropriate unit of concentration for thermodynamic calculations is molality (rnolkg ). Thus, concentration units given in molarity (moll ) need to be converted into units of molality. This is a rather straightforward calculation, requiring only the density of the solution (in kgl ) for the conversion. The molality can be calculated from molarity via Eq. (4.11) as shown, for example, by Brown, Curti and Grambow (2005) in the NEA reviews of the chemical thermodynamics of elements important in the nuclear industry  

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