SYNTHESIS OF NEW ELECTROLYTES IN SOLUTIONS WITH dc CURRENT
1607
being synthesized, and anolyte. With this information
available, the calculation can be performed as follows.
Let there exist two electrolytes (C A and C A )
1
1
2
1
of equal concentrations. The equivalent electrical con-
ductivity ( ) of C A solution is given by
1
1
(1) The cation transference number is found for
the chosen catholyte concentration from the depen-
dences of the ion transference numbers for the catho-
lyte on its concentration.
=
F(uC1 + v ),
(4)
C A
A
1
1
1
and that of C A solution by
2
1
(
2) The concentration and the cation transference
=
F(uC2 + v ).
A1
(5)
number of the electrolyte being synthesized are found
graphically from the concentration dependence of
the ion transference numbers of the catholyte and
the electrolyte being synthesized [8].
C2A1
As the solutions have a common ion (anion) the
mobility of the noncommon ion (cation) will be higher
for that solution, which has a higher equivalent elec-
trical conductivity. Therefore, a stable interface be-
tween the solutions will be formed if the electrolyte
having a higher equivalent electrical conductivity is
situated ahead of that with a lower electrical conduc-
tivity in the direction of motion of noncommon ions
in the electric field. Hence follows that synthesis of
a new solution on bringing in contact two solutions
containing four different ions yields an electrolyte
whose equivalent electrical conductivity is lower than
that of each of these solutions at a concentration equal
to that of the starting solutions. Let us consider, as
an example, choice of electrolytes in interaction of two
(3) The anion transference number of this solution
is found from the cation transference number of the
catholyte being synthesized.
(4) The concentration and the anion transference
number of the anolyte are found, also graphically, from
the concentration and the anion transference number
of the electrolyte being synthesized and from the con-
centration dependence of the ion transference numbers
of the anolyte [8].
(5) The resulting solution concentrations and ion
transference numbers can be used to find the mobil-
ities appearing in relations (1) and (2).
+
+
solutions containing four different ions: K , Na , Cl ,
and NO . Four different compounds can be formed
3
(
6) The ion mobility is calculated by the formula
from these ions: KCl, KNO , NaCl, and NaNO .
3
3
The equivalent electrical conductivities of aqueous
solutions of these compounds at a concentration of
2.0 g-equiv l 1 and temperature of 18 C are as follows:
u = T / Fc,
(3)
2
1
1
where u is the ion mobility (cm V s ); T, ion trans-
ference number; , electrical conductivity of the solu-
1
1
1
Substance
,
KCl KNO3 NaCl NaNO3
92.3 69.0 66.6 54.4
tion (
cm ); F, Faraday number (C g-equiv );
1
g-equiv 1 cm2
1
and c, solution concentration (g-equiv l ).
However, the above calculation procedure can be
only used in very rare cases because of the complete
lack of data on how the ion transference numbers de-
pend on the solution concentration at high concentra-
tions, for which such a synthesis is the most promis-
ing. In addition, the solution concentrations do not
necessarily satisfy the steady-state conditions in syn-
theses of new substances.
It can be seen from the electrical conductivity data
that the following compounds cannot be synthesized:
(1) KCl, whose electrical conductivity is the highest;
(2) KNO , whose electrical conductivity is lower than
3
that of only a single solution; and (3) NaCl, whose
electrical conductivity is lower than that of two solu-
tions (KCl and KNO ), but these solutions contain
3
no sodium ions and, therefore, cannot be used in syn-
thesis.
Synthesis can be performed at equal solution con-
centrations. In this case, the choice of starting electro-
lytes is not difficult if the ion mobilities are only
roughly estimated (higher or lower). The electrolytes
are chosen by comparing the ion mobilities of solu-
Only an NaNO solution can be synthesized in
3
pure form. As starting solutions for this synthesis
can serve only KNO and NaCl solutions containing
3
four different ions and having an equivalent electrical
1
tions having equal concentrations (g-equiv l ) and
conductivity exceeding that of the NaNO solution.
3
a common ion. This evaluation method, suggested in
This principle of electrolyte selection was used when
carrying out this synthesis in practice. In those cases
when no data are available on the equivalent electrical
conductivities of solution, the electrolytes can be
chosen experimentally.
[
9], is worthwhile in practice in studying the separa-
tion of electrolyte mixtures in concentrated solutions
by ion mobilities. Let us illustrate this technique by
the following example.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 78 No. 10 2005