1070-4272/05/7808-1370 + 2005 Pleiades Publishing, Inc.
Russian Journal of Applied Chemistry, Vol. 78, No. 8, 2005, pp. 1370!1372. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 8, 2005,
Original Russian Text Copyright + 2005 by Yurkinskii, Firsova, Petrova.
Complexation of Lead(II) Ions with Hydroxide Ions
in Nitrate-Chloride Solutions
V. P. Yurkinskii, E. G. Firsova, and N. V. Petrova
St. Petersburg State Polytechnical University, St. Petersburg, Russia
Received April 19, 2005
Abstract-Complexation of lead(II) ions with hydroxide ions in nitrate-chloride solutions at 298 K was
studied using potentiometric titration.
The search for the optimal composition of the al-
kaline electrolyte is an important technological task in
processing of scrap lead accumulators with an active
paste containing lead(II) oxide .
The high solubility of PbO in alkaline solutions
is known to be due to formation of strong lead(II)
hydroxide complexes [2, 3]. The presence of both
organic and inorganic admixtures and, in particular,
chlorides in alkaline solutions strongly affects the
complexation of lead(II) ions . For example, it
was found in  that mixed lead(II) hydroxidechloride
complexes are formed at low alkali concentrations
(<0.4 M) in a solution containing a mixture of sodium
chloride and hydroxide.
Proceeding with the studies [4, 5], we examined
the complexation of Pb(II) in mixed nitrate-chloride
solutions containing sodium hydroxide as an additive
in order to analyze the effect of the concentration of
chloride ions on the formation of lead hydroxide com-
plexes and, if possible, to determine the composition
of mixed chloride-hydroxide complexes.
The complexation of lead(II) ions was studied by
potentiometric titration at 298 K. The experimental
technique and the electrochemical cell have been
described earlier [4, 5].
We used as a supporting electrolyte aqueous solu-
tions containing a mixture of sodium nitrate (0.33
1.0 M) and sodium chloride (030.7 M) with concen-
trations that allowed us to obtain a solution with
an ionic strength equal to unity (in the limiting case,
no sodium chloride was present, and the nitrate con-
centration was 1.0 M).
The potentiometric titration was carried out with
a sodium hydroxide solution containing sodium chlo-
ride, the concentrations of NaOH and NaCl being
equal to the concentrations of NaNO
and NaCl, re-
spectively, in the supporting electrolyte. This allowed
us to maintain a constant ionic strength in a solution
under study during all the experiments.
The half-cell of the electrochemical cell under
study can be represented as:
, NaOH, NaCl, (1)
where Pb(Hg) is a lead amalgam electrode.
A typical dependence of the potential of the amal-
gam electrode on the logarithm of the alkali concen-
tration in solutions containing sodium chloride is
shown in Fig. 1. It can be seen that the E3lnc
Fig. 1. Potential of the indicator electrode, E, vs. the loga-
rithm of the total concentration of hydroxide ions lnc
in solution. Supporting electrolyte (M): 0.7 NaNO
0.3NaC1 + 1 10
) Total concentration
of hydroxide ions.