Question

How can the empirical formula of a compound be experimentally found?

Answer 1

By burning a known mass.

Explanation:

Microanalysis of organic compounds typically takes an accurate mass of unknown compound and burns it under controlled conditions. So if you take the generic `C_nH_mO_p`, and burns it, you get the combustion products, `CO_2`, and water.

The combustion products are shunted to a gas chromatograph, where their percentage composition may be very accurately measured. The result is a percentage BY MASS of `C` and `H`, and (in a separate experiment depending on the analyzer) `N`. There should be other answers on these boards that go into more detail.

For compounds containing metals, or other elements, there are other means to determine the elemental composition.