Ok,
(A) Fe 2+ + MnO4 - -> Fe 3+ + Mn2+
First step : Asign the oxidation numbers
Fe ( Iron ) has an oxidation number of +2 as it's equal to it's charge.
MnO4 ( Permanganate )'s oxidation number is the oxidation number of Mn as it's unknown :
The over all oxidation number has to equal to -1 and we know from the rules that at most times Oxygen has an oxidation number of -2
Mn + 4 ( O ) = -1
Mn +4(-2) =-1
Mn + (-8) = -1
Mn=+8 + ( -1)
Mn=+7
The oxidation number of Fe +3 is equal to it's charge i.e +3
Same for the oxidation number of Mn is equal to +2.
Write the oxidation numbers under the equation.
Fe2+ + MnO4 - -> Fe 3+ + Mn 2+
+2 +7 +3 +2
Now identify what is oxidised and reduced.
Oxidation is the loss of electrons where Reduction is the gain of electrons.
Ok so oxidation number of Fe +2 goes to +3 that means it looses one electron ( e- ).
That means it's oxdised.
The oxidation number of MnO4 - goes from +7 to +2 that means it gains five electrons i.e it's reduced.
To balance the equation we know that in order for MnO4 - to be reduced we need 5 electrons. When something is reduced something has to be oxidised.
Therefore we need 5 Fe +2 to give up 5 electrons.
The ratio is 5:1
5Fe 2+ + MnO4 - -> 5Fe 3+ + Mn +2
Hope this helps the reaction is not complete though as you gave me the proper reaction is as fallows.
5Fe 2+ + MnO4 - + 8H + -> 5Fe +3 + Mn 2+ + 4H2O
