what is the weight of iron contained in 100g of an iron ore which is 80% hematite, Fe2O3
I was wondering the same question myself today
In the 100 g of iron ore, you have 80% (or 80 grams) of Fe2O3. The molecular weight of Fe2O3 is 159.69. The atomic weight of Iron is 55.85, and you have 2 Fe per mole Fe2O3. Therefore, you can take a siomple ratio of iron and Fe2O3: Grams Fe [2* (Weight Fe)/(Weight Fe2O3)] x 80 grams (55.85*2/159.68869*80) 55.96 grams. Now, you teacher really only gave you one sig fig with the data, so really you should only report one sig fig in the answer: 60 grams. As I tell everyone, report both numbers, explaining that since you were restricted to one sig fig, you need to report only one (but giving the other number shows you know what you are doing!). Hope that helped!
