I have always had the notion of calculating weight percentage of Fe in FeO. It always seems that we are to calculate at times the weight percentage of FeO in Fe.Particularly when one weight percentage is involved.However "weight percentage of FeO in Fe" is something that seems extremely ridiculous on my part.I would be extremely grateful if someone can correct my wrong notion/give me an intuition to what I am asking for.
Based on the comments and extended chat, this is the kind of question the OP actually wanted to ask: Consider a mixture of Fe and FeO. The total percentage (by weight) of iron is 86.638%. What is the percentage of iron metal in the mixture?
Answer: For simplicity, assume exactly 100 g of the mixture. Hence the total iron is 86.638g and the remaining 13.362g is oxygen. Therefore, the number of moles of oxygen atoms is 0.83516 moles, i.e., 13.362g divided by 15.9994g/mole. This is also the number of moles of Fe in FeO, so the mass of Fe in FeO is 46.639g, i.e., 0.83516 moles times 55.845 g/mole. Subtracting this from 86.638g yields 39.999g metallic iron. So the 100 g of mixture was 39.999g of Fe and 60.001g of FeO, i.e., 40% Fe and 60% FeO.