one technique for determining empirical formulas in the laboratory, used for compounds with primary H and C,
steps:
1. find the grams of carbon from the mass of CO2 and hydrogen from the mass of H2O
2. once you find the mass of H and C you find the weight of the third element (aka O) by , Mass of O= mass of sample - (mass of C + mass of H)
3. then you find the empirical formula of that compound