# What is the mass in grams of one formula unit of Fe2O3?this the only information that is given I know the Mole Mass which is 159.68 g/mol (rounded to 2 decimal points) but I am just stumped as to...

## What is the mass in grams of one formula unit of Fe2O3?

this the only information that is given

I know the Mole Mass which is 159.68 g/mol (rounded to 2 decimal points) but I am just stumped as to where to go from there.

ncchemist | Certified Educator

The phrase "formula unit" is a little confusing here.  Generally, when you are talking about the mass of a chemical formula you are talking about the molar mass which you already have.  159.68 is the mass in grams for one mole of Fe2O3.  If by formula unit you mean the smallest possible unit of Fe2O3, then you are talking about one molecule of Fe2O3.  Since the formula weight is grams per mole and there are 6.022 x 10^23 molecules in a mole, you would divide the molar mass by 6.022 x 10^23 to get the mass in grams per molecule.

159.68 g/mol (1 mol/6.022 x 10^23 molecules) = 2.65 x 10-22 grams in a single molecule of Fe2O3