276
1. Grenthe
ie. Yis a linear function of g(aI 1I2 ), with the slopeXzI !:,.ZZ and the intercept (Xl - Myl 2) I !:,.ZZ.
a is a fixed empirical Pitzer parameter equal to 2.0 kg1l2 mor l12 for all electrolytes. Y
can be calculated from the known ionic strength, the Debye-Hiickel parameter A,p and
IJ.Ix, i.e. the known value of pI) for the 1-1 ionic medium electrolyte. The values of g(a[1I2)
are obtained from the ionic strength of the solution.
In Fig. 10.3 we have plotted the values of Y for some common 1-1 ionic media.
The linearity is goo~ for all electrolytes considered, and the values of the parameters (Xl - M:yl 2) l/j"Zz and XzI !:,.ZZ determined for each electrolyte are given in
Table 10.2. As these parameters, especially the slope, do not vary much with the nature
of the 1-1 electrolyte, one can use all the data to determine one common set of parameters (see the last line of Table 10.2) where the uncertainties are given as 30'. This findFig. 10.3. The relationship between the SIT parameters !If
030
1
• NaCI0 4
and the Pitzer parameters !lifO)
o NaCi
and !llfl) for reactions studied
.. KN0 3
in different 1:1 ionic media. The
0.25
• NaN03
symbols denote calculated vale LiCI0 4
ues of Yas a function of g(Im)
/:;, HCI0 4
using Eq. 10.30
0.20
~
;'
~
«'
... . ; '
)..
0.15
0.10
0.05
0.00
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
g(lm)
Table 10.2. Quantitative relationship between the Pitzer and SIT model parameters for chemical reactions in different ionic media at 298.15 K
1:1 ionic medium ele.ctrolyte
(Xl -!If/ 2) , !lZ2
X2' !lZ2
NaCI0 4
0.031
0.340
LiCI0 4
0.038
0.348
Hcl°4
0.032
0.342
NaN0 3
0.026
0.334
KN0 3
0.019
0.327
NaCI
0.030
0.332
All data
0.029 ±O.OOS
0.337 ±0.014