Handbook of Solvents - George Wypych - ChemTech - Ventech!

622 Victor Cherginets
Ω= 14 − pK + pO
l
2−
taking into account [10.4.15] eq. [10.4.16]
( 14 )
Ω= − pK + pI + pO
[10.4.16]
2−
KCl −NaCl
l [10.4.17]
where (14 - pK KCl-NaCl)istheΩvalue in KCl-NaCl standard solution (pO=0) and pO 2- is the
instrumental pO in the solvent studied.
Therefore, the shift of pO scales vs. KCl-NaCl depends only on the I l value. On the basis
of [10.4.13] it has been estimated as +7-8 log units (Figure 3 25 ) for KCl-LiCl at 1000K.
Homogeneous Lux acid-base equilibria of type of [10.4.6] have not been earlier considered
as available for estimations of oxoacidity indices. However, pK for these reactions
may be written as
pK
NB
=− log = pK KCl −NaCl
+ pI l
[10.4.18]
N N I
− ( 2 − )
1 1
A O l
For the use of this type of equilibrium it is necessary to make the following non-thermodynamic
assumption:
⎛ γ
⎜
⎝ γ
B
⎞
⎟
⎠
A l
⎛ γ
= ⎜
⎝ γ
B
⎞
⎟
⎠
A KCl −NaCl
[10.4.19]
where:
γ corresponding activity coefficients of the acid and the base in solvent “l” and KCl-NaCl
The use of [10.4.16] where A and B are anion acid and base for estimations of the
oxobasicity indices may be justified because the acid and the conjugated base are negatively
-2 -2
charged (in the pair Cr2O7 /CrO4 they are of the same charge).
Finally, let us consider the usability of the oxide solubility data
MeO = Me + O
s
2+ 2−
for pI l estimations. The solubility product value, P, may be presented as
or
− ( )
P = N N I = P I
1 −1
MeO, l 2+ Me
2−
O l MeO, KCl −NaCl
l
pP = pP −pI
MeO, l MeO, KCl − NaCl l
[10.4.20]
[10.4.21]
[10.4.22]
Metal cations in molten halides form halide complexes. The reaction [10.4.20] for
chloride melts (N Cl - =1) suggests that the distribution of Me 2+ between different complexes
MeCl n 2-n remains unchanged (similarly to eq. [10.4.10]-[10.4.12] for the oxide ion distribution).
It is clear that the solubility data may be used for estimations of the oxoacidity indices
only in melts with the same anion composition. The anion changes cause errors since Me 2+
in eq. [10.4.21] is referred to essentially different acids, e.g., halide complexes MeCl 4 2- and