Figure 6.8
Titration of halides with silver nitrate. (a) Titration of iodide with AgNO 3.^
(b) Titration of a mixture of chloride, bromide and iodide with AgNO 3.Theoretical (dotted line) and experimental (continuous line) titration curves for such a mixture are
shown in Figure 6.8(b). The formation of mixed crystals and solid solutions limits the accuracy to 1–2%
when the halides are present in similar concentrations.
Redox Titrations
Platinum indicator electrodes respond to the ratio of oxidized to reduced forms for such oxidants as
and reductants such as. The
titration curves are often asymmetrical due to the stoichiometry of the reaction, but the error is small (<
1%) or can be eliminated by titrating standards. If the reduction potentials of two species differ by > 0.2
V, separate inflections will be observed when titrating the mixture, e.g. the titration of Fe2+ and Ti3+
with potassium permanganate.
Some redox systems are slow to reach equilibrium at a platinum electrode after the addition of an
increment of titrant, e.g.
For titrations involving those species, the response can be improved by forming a cell from a pair of
identical platinum electrodes and passing a very small constant current (~ 5 μA) between them
throughout the titration. As electrolysis is negligible, the solution composition is virtually unaffected by
the passage of the current. The break in the titration curve is usually sharp and can be 100–200 mV or
more. The use of a pair of platinum electrodes may be particularly advantageous if contamination of the
sample