Question

How to prove empirical and molecular formulae?

Answer 1

`"How to prove.........?"`

Explanation:

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 `%C` and `%H` by mass in the sample, and we can use these percentages to find the empirical formula (and you must have done examples of these problems). `%N` can also be measured directly as nitrogen comes off as `NO_2(g)`.

If the material contains oxygen, then the missing percentage is assumed to be due to `%O`. Halide percentage may be measured by a Mohr titration.