In what other ways can you make use of the concept on percentage composition?

You can find the empirical/molecular formula by using the percent composition.

This video discusses using experimental data to calculate a . video from: Noel Pauller

In the video the percent composition is found to be... Fe = 77.6% O = 22.4%

This video uses the experimental data to find the empirical formula of FeO. video from: Noel Pauller

So what if you don't have experimental data, just the percent composition? Assume you have a 100g sample, which would mean 77.6g of Fe and 22.4g of O.

Do the calculation just like in the second video:

##((77.6g Fe)/1)x((1 mol Fe)/(55.84 g Fe)) = 1.4 mol Fe##

##((22.4g O)/1)x((1 mol O)/(16.00 g O)) = 1.4 mol O##

You can see the ratio of Fe:O is 1:1 meaning the reaction produced FeO with the iron having an oxidation state of +2.