Potassium permanganate (KMnO4) is widely used in titrations,
as it is a versatile oxidising titrant.
In aqueous solutions, potassium permanganate is completely dissociated
K+ ions which are stable and non-reactive in aqueous
ions which are the reactive component of the solution.
Click below to view an animation that illustrates potassium permanganate
has an intense purple colour, which imparts a visible pink tinge
to aqueous solutions, even when the ion is present only in small
concentrations. This intense colour is extremely useful, since the
presence of the
ion can be detected by the presence of this pink colour. Because
of its intense colour, the
ion serves as its own indicator, so there is no need to add an indicator
as is usually required.
Potassium permanganate is not a primary standard, and preparation
of the solution will always cause formation of solid manganese dioxide
Solutions of potassium permanganate must be filtered before being
used, to remove the manganese dioxide precipitate. Potassium permanganate
solutions are unstable, and must also be filtered after long periods
of storage, because manganese dioxide (MnO2) will precipitate
out during storage.
KMnO4 reacts differently depending on whether it is
used in acidic, neutral or alkaline solutions.
At SimuLab, the standardisation of KMnO4 is carried
out under the following conditions:
sodium oxalate (Na2C2O4) is
the primary standard used
the titration is carried out in an acidic solution (an excess
of sulfuric acid is added to the sodium oxalate before the titration)
Na2C2O4 is accurately weighed
into an Erlenmeyer flask
1M H2SO4 is added to the Erlenmeyer flask
to produce an acidic sodium oxalate solution
KMnO4 solution is added to the flask from the burette
until the first permanent pink colour persists in the flask. The
pink colour indicates an excess of permanganate ions, because
all the oxalate ions in the flask have reacted, and the end point
of the titration has been reached.
To view an animation which illustrates the standardisation of
KMnO4 click below.