posted by aduma .
a gaseous compound of carbon and hydrogen contains 80% carbon by mass, one dm3 of the compound at s.t.p weighing 1.35g. calculate
assume you have 100 grams.
then 80 grams is carbon, or 80/12 moles
and 20 grams is H, or 20/1 moles H
divide each by the lowest
H=3 empirical formula: CH3
Now, 22.4 liters has a mass of 1.35*22.4 = 30.24grams
divide that by the empirical mass
Molecular formula: twice the empirical formula, or C2H6
Your instructor is just too easy.