Question time! It's been a while.
How do we know whether iron has been reduced or oxidised in a
redox reaction if the question does not explicitly state so?
For e.g. Potassium manganate (VII) + Iron (II) ethanedioate
I don't think iron is oxidised in this case.
Oh yeah, it applies to other cations with variable oxidation
states too (copper, zinc, ... those oh-so-unstable-cations)
Thanks for the clarification.
If the molarities are all 1.0 mol/dm3, check the Data Booklet
values. If the reduction potentials and standard potentials show
feasibility, then redox will occur. Check if the cation, the anion,
neither, or both, will react with the oxidizing agent.
Of course, the molarities are hardly ever 1.0 mol/dm3. Hence, if
the question does not specify or provide sufficient information,
make a reasonable educated assumption (and state your assumptions),
and proceed with calculations accordingy.
In this case, based on Data Booklet values, and in the
case of relatively similar enough molarities, you may
justifiably assume that MnO4- is powerful enough to oxidize
both cation and anion. Write two separate sets of half-equations to
obtain two separate balanced redox equations, and proceed to
calculate the required values based on the stoichiometry of the
balanced redox equations.