The composition of a compound is 20.01% carbon and 79.99% oxygen by mass. what is its empirical formula?

Assume there are 100g of the compound.

Mass of carbon:20.01g

Mass of oxygen:79.99g

Number of mole of carbon:20.01/12=1.6675mol

Number of mole of oxygen:79.99/32=2.4996875mol

Mole ratio between carbon and oxygen:

1.6675/1.6675:2.4996875/1.6675

=1:1.499062969

1x2:1.499062969x2

=2:2.998125937

≈2:3

Hence, the empirical formula:

C2O3