Page 48 - MODERN ASPECTS OF ELECTROCHEMISTRY

35
Voltaic Cells in Electrochemistry and Surface Chemistry of Liquids
W
The Volta potential at the water/nonaqueous solvent boundary, ∆ S ψ,
maybe measured as the difference in the compensating voltages of the
following cells 15,19 :
s | w ||
M vib.pl gas | || SCE M,E8 (VIII)
+
+
M +X - | M +X || -
| ||
||
W ||
M vib.pl gas || SCE M, E
+
M + X - 9 (IX)
||
where w and s denote the mutually saturated aqueous and organic phases,
respectively, which contain the salt MX :
W
S
∆ Ψ(MX )=E 8 -E 9 (22)
W
The reliability of the experimental ∆Sψ (MX) values was checked for
systems containing nitrobenzene, 93-97 nitromethane, and 1,2-dichlo-
98
roethane as organic solvent by comparing the differences in thesevalues
for various pairs of salts with the differences in the Galvani (i.e.,distribu-
W
tion) poterntials, ∆ S ϕ (MX ) for the same pairs. The differences should be
W
W
the same. 15,19 The∆ S ϕ or ∆ SΨ data can be used to estimate ion solvation
energies in a water-saturated solvent. 15,94
_
The liquid liquid patition systems discussed above are in fact very
similar to various membrane-type interfaces and may serve as a model for
them.A good example is, for instance, the distribution of a dissociated salt
between an aqueous solution and a permeable organic polmer. 99
The possibility of measuring a nonequilibrium liquid junction (diffu-
sion) potential by using voltaic cells has been checked also 100,101 :
w s | ||
| ||
+ -
+ -
SCE M X gas M X M X || SCE E
1 1 |
a 1 a 2 | || (X)
l.j.
The compensating voltage of the cell maybe expressed bythe
relation:
E=E = E +∆ a χ W (23)
a
*
2
l.j.
l.j.
1