ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 2, pp. 269!271. + Pleiades Publishing, Inc., 2006.
Original Russian Text + A. I. Demidov, M. S. Kokhatskaya, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 2, pp. 269!271.
AND CORROSION PROTECTION OF METALS
Effect of the Concentration of Solutions being Titrated
on the Shape of Conductometric Titration Curves
A. I. Demidov and M. S. Kokhatskaya
St. Petersburg State Polytechnic University, St. Petersburg, Russia
Received December 29, 2005
Abstract-The influence exerted by the concentration of solution being titrated on the shape of the theoretical
curves of conductometric titration was studied. The concentrations at which the equivalence points are clearly
observed in the conductometric titration curves were determined.
Conductometric titration is a technique in which
the equivalence point is found by measuring the elec-
trical conductivity of a solution being analyzed.
The conductivity changes as a result of chemical re-
actions between the titrant and the substance being
determined that occur in the course of titration .
Commonly, theoretical curves of conductometric titra-
tion are plotted using the electrical conductivities
of infinitely diluted solutions . Because the total
electrical conductivity of a solution depends on its
concentration, the increase in the initial concentration
of a solution being titrated affects the shape of a con-
ductometric titration curve. This can impair the ac-
curacy of analysis and make narrower the areas of its
In the study, the influence exerted by the concen-
tration of the solutions being analyzed on the shape
of the theoretical curves of conductometric titration
was demonstrated for the example of titration of so-
lutions containing sodium hydroxide, sodium carbon-
ate, mixtures of sodium hydroxide and sodium car-
bonate, and those of sodium carbonate and sodium hy-
drocarbonate with sulfuric acid. The concentrations at
which the equivalence points are clearly manifested in
the conductometric titration curves were determined.
The solutions mentioned above were analyzed in
processing of worked-out nickel!iron (NI) batteries,
in which aqueous sodium hydroxide solutions are
the most frequently used as electrolyte. The drawback
of alkaline electrolytes is their susceptibility to car-
bonization, which mainly occurs via absorption of
atmospheric carbon(IV) dioxide. In storage of worked-
out NI batteries in air, the electrolyte remaining in
pores of the active paste undergoes further carboniza-
tion. As a result, sodium hydroxide is converted into
sodium carbonate, and the carbonate, into hydrocar-
The theoretical dependences of the electrical resis-
tivity of the solutions on the number of titrant equiv-
alents were constructed using data from the reference
book . In doing so, the dilution of the solution be-
ing analyzed during titration was disregarded. The cal-
culation was performed for solutions with an initial
concentration of a substance (or substances) to be
determined equal to 0.01!0.1 N. The concentration
of the titrant was 0.1 N in all cases.
In titrating a sodium hydroxide solution with
a standard solution of sulfuric acid, the total electrical
conductivity of the solution, ?
, varies as follows:
before the equivalence point, at 0 < y <1,
(1 3 y)+c
at the equivalence point, at y =1,
after the equivalence point, at 1 < y <2,
(y 3 1),
is the electrical conductivity of the initial
solution of sodium hydroxide; ?