,
Cr2O7
2– + 14 H
+ + 6 Fe
2+ ® 2 Cr
3+ + 6 Fe
3+ + 7 H2O
Potassium permanganate KMnO4
Potassium permanganate is prepared by fusion of MnO2 with an alkali
metal hydroxide and an oxidising agent like KNO3 This produces the
dark green K2MnO4 which disproportionates in a neutral or acidic
solution to give permanganate 2MnO2 + 4KOH + O2 ® 2K2MnO4 + 2H2O
3MnO4
2– + 4H+ ® 2MnO4
– + MnO2 + 2H2O
Commercially it is prepared by the alkaline oxidative fusion of MnO2
followed by the electrolytic oxidation of manganate (Vl) F
used with KOH, oxidised
with air or KNO
2
3
2
4
MnO
MnO
;
manganate ion
−
→
42
4
Electrolytic oxidation in
alkaline solution
MnO
MnO
manganate
permanganate ion



Rationalised 2023-24
107
The d- and f- Block Elements
In the laboratory, a manganese (II) ion salt is oxidised by
peroxodisulphate to permanganate