How to Identify Iron Valence in Multiple Valence Compounds

[supernova1203]

I found a list of all the possible valences of all elements online, but say were dealign with a compound with iron, has multiple valences, how do i know which valence to use when?

this has been bugging me for quite some time, any ideas?

 

[Borek]

There is no simple answer to that. For example, iron has (at least) three oxides, FeO, Fe₂O₃ and Fe₃O₄. Each is stable in different situations, each contains iron atoms in different oxidation states. Which, when and why - that's what the whole chemistry is about.