How to prove empirical and molecular formulae?
You can seldom prove anything unequivocally in science. You can find data that are consistent with a theoretical framework.
And the yard stick of consistency is evidence gathered from some (or several) experiments.
To find the empirical formulae of alkanes............alkynes etc., take a known mass of hydrocarbon, combust it in a furnace, and collect the combustion gases of carbon dioxide, and water. The quantities of water and carbon dioxide may be very precisely measured (by gas chromatography). They are usually reported as
If the material contains oxygen, then the missing percentage is assumed to be due to