The
half-reactions are noted below:
6 I
– ® 3I2 + 6 e
– ;
3 Sn
2+ ® 3Sn
4+ + 6 e
–
3 H2S ® 6H
+ + 3S + 6e
– ;
6 Fe
2+ ® 6Fe
3+ + 6 e
–
The full ionic equation may be obtained by adding the half-reaction for
potassium dichromate to the half-reaction for the reducing agent, for e g ,
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