# What is the percentage by mass of iron (Fe) in the mineral hematite (Fe_2O_3)?

Dec 5, 2016

69.9% to three significant figures.

#### Explanation:

First find the total mass of the compound

$3 \times 15.999 = 48$ grams for Oxygen

$2 \times 55.8 = 111.6$ grams for Iron

adding these gives 159.6 grams per molecules $F {e}_{2} {O}_{3}$

Now divide the mass of Iron by the total mass for the compound.

$\frac{111.6}{159.6} = .6992481$ Change this to a percentage by multiplying by 100 and round off to three significant figures gives

69.9 % Iron.