Determine the mass in grams of each element in the sample. If you are given percent composition, you can directly convert the percentage of each element to grams.
For example, a molecule has a molecular weight of 180.18 g/mol. It is found to contain 40.00% carbon, 6.72% hydrogen and 53.28% oxygen.
Convert the percentages to grams.
40.00 grams of carbon
6.72 grams of hydrogen
53.28 grams of oxygen