Handbook of Solvents - George Wypych - ChemTech - Ventech!

1008 An Li
Figure 14.21.2.2a. Deviations from log-linear model (equation [14.21.2.2], triangle) and the extended log-linear
model (equation [14.21.2.10], circle) for solute naphthalene in various water cosolvent systems. Experimental data
are from Ref. 83.
tures. However, none of the properties consistently predicted the extrema of the deviation,
although density corresponded in several cases.
Non-ideality of a mixture is quantitatively measured by the excess free energy of mixing.
From this standpoint, Pinal et al. 75 proposed that a term Σ(f i ln γ i) be added to equation
[14.21.2.4] to account for the effect of the non-ideality of solvent mixture:
ii ( m )
log S / Sw= ∑σifi+ 2. 303 ∑filogγi
[14.21.2.10]
where γ i is the activity coefficient of solvent component i in solute-free solvent mixture.
Values of γ‘s can be calculated by UNIFAC, a group contribution method for the prediction
of activity coefficients in nonelectrolyte, nonpolymeric liquid mixtures. 88 UNIFAC derived
activity coefficients are listed in Table 14.21.2.3 for selected cosolvent-water mixtures.
They are calculated with UNIFAC group interaction parameters derived from vapor-liquid
equilibrium data. 89,90
The difference between the experimental log S m and that predicted by the extended
log-linear model, i.e., equation [14.21.2.10], is