Page 28 - Pharmaceutical Analytical Chemistry II - Pharm D Clinical- 07-PA202
P. 28
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
27