Figure 6.15
Amperometric titration curves.
(a) Only substance titrated is reducible, e.g. Pb2+ against , Ag+^
against halide.
(b) Only titrant is reducible, e.g. against Pb2+, Na 2 S 2 O 3 against I 2.^
(c) Both reducible, e.g. Pb2+ against , Cu2+ against α-benzoin oxime.speed of 600 min–^1 or more. These are generally some twenty times larger than the currents derived
from a DME because of mechanical convection created by the rotation. The rotating electrode is
particularly useful for redox titrations involving such species as Br 2 and Fe(III) but the low hydrogen
activation overpotential for platinum limits its applications to alkaline or weakly acid conditions. It is
very sensitive to the presence of dissolved oxygen.
Bi-amperometric Titrations
Two identical stationary micro-electrodes (usually platinum) across which a potential of 0.01–0.1 V is
applied can be used in place of either the DME or the rotating platinum micro-electrode. The
equivalence point is marked by a sudden rise in current from zero, a decrease to zero, or a minimum at
or near zero (Figures 6.16(a), (b) and (c)). The shape of the curve depends on the reversibility of the
redox reactions involved. The two platinum electrodes assume the roles of anode and cathode, and in all
cases a current flows in the cell only if there is a significant concentration of both the oxidized and
reduced forms of one of the reactants. In general, two types of system can be envisaged:
Figure 6.16
Bi-amperometric titration curves.
(a) Both electrode reactions reversible, e.g. Fe2+ against Ce4+.^
(b) Only titrant reaction is reversible, e.g. against I 2.^
(c) Only substance titrated is reversible, e.g. I 2 against Na 2 S 2 O 3.