Page 29 - Pharmaceutical Analytical Chemistry II - Pharm D- 02-06-07102

I- Potassium permanganate, KMnO4
Properties

It is a strong oxidant with an intense violet color
It is not a primary standard
Standard solution and stability

Aqueous solutions of MnO4− are not entirely stable because the
ions tend to oxidize water:

4MnO4− + 2H2O 4MnO2 (s) + 3O2 (g) + 4OH−

This decomposition reaction is catalyzed by light, heat, acids,
manganese dioxide.

Potassium permanganate should be stored in dark glass bottles &
kept away from high temp

Standardization 2Mn2+ + 10CO2 + 8H2O
colorless
It is standardized ≠ st. oxalic acid

70 o C

2MnO4− + 5H2C2O4 + 6H+
Purple
End point detection

Self indicator
The intense purple color of MnO4− serves as indicator

Reduction half-reactions
Strongly acidic solutions (pH ≤ 1)

MnO4− + 8H+ + 5e Mn2+ + 4H2O E0 = +1.51 V
Purple manganous
(colorless)

Change in oxidation state of Mn: +7 to +2

Eq wt = Mw / 5

Eqwt for redox reactions = Mwt / no. of electrons transferred per
one mole of substance

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