How many kilograms of iron are in 639 kilograms of Fe2O3?

Answer 1

First you need to find the atomic weights of all the elements involved and add them up (including how many atoms of the same element there are) to find the total molecular mass.

Fe = 55.9 grams × 2 atoms = 111.8 grams
O = 16 grams × 3 atoms = 48 grams
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Fe2O3 = 159.8 grams

Then you take the weight of iron in one mole of the compound and divide it by the total weight to get its percent composition.

111.8 grams Fe ÷ 159.8 Fe2O3 grams = .6996 = 69.96% Fe in Fe2O3

Then we apply this percentage to 639 kg. The thought process is as follows: if there is 69.96% of iron in Fe2O3 by weight, then 69.96% of 639 kg of the substance is iron.

69.96% of 639 kg = .6996 × 639 = 447.1 kilograms of Fe in 639 kilograms of Fe2O3