Why does not potassium permanganate react with #Fe(+III)# salts?

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Answer 1 · 2017-12-02T10:56:51

Well you are using a strong oxidant (potassium permanganate) on ferric ion....#Fe(+III)#....the which is already oxidized..

It might be better if the reaction formulated as the action of permanganate ion on ferrous ion, i.e. in #FeSO_4#...

#Fe(+II)# is oxidized to #Fe(+III)#

#Fe^(2+) rarr Fe^(3+) + e^-# #(i)#

#"Permanganate ion"# is reduced to #Mn^(2+)#:

#MnO_4^(-) + 5e^(-) +8H^+ rarr Mn^(2+) + 4H_2O# #(ii)#

We take #5xx(i)+(ii)# to eliminate the electrons....

#5Fe^(2+) +MnO_4^(-) + 5e^(-) +8H^+ rarr Mn^(2+) + 4H_2O#

And what would we see in this reaction? The deep purple colour of permanganate anion would dissipate to give colourless #Mn^(2+)#.