THE EXTRAPOLATION OF EXPERIMENTAL EQUILIBRIUM-CONSTANT DATA TO ZERO IONIC-STRENGTH - CRITICAL-REVIEW AND NEW APPROACH

Different Debye-Huckel expressions for the activity coefficients of sp ecies in aqueous solution in the ionic strength range I = 0-3.5m (3M) are used for the extrapolation of equilibrium constants data to I = 0 and the interpolation to unknown I values. This may be accomplished us ing four or more values of the equilibrium constants that are equally well distributed on the I scale. The interpolated and extrapolated equ ilibrium constant values obtained are quite satisfactory and within th e experimental error of the corresponding equilibrium constants. The v alues at I less-than-or-equal-to 0.1 are very important as they can pa rticularly influence the equilibrium constant value calculated at I = 0 and for which the error can reach 0.1 log unit or more. The values a t I greater-than-or-equal-to 1.5 can also influence the extrapolated v alue at I = 0 and the interpolated value at a given I when an inadequa te extrapolation model is selected. Among the expressions used, only t hose with two or more unknown parameters are suitable for such calcula tions.