Question

What is an empirical formula?

Answer 1

It's a ratio formula of all the elements in the compound.

Explanation:

A ratio formula doesn't say anything about the actual numbers of atoms and how they are interconnected.

Example:
By burning a carbon-hydrogen compound and measuring the water and `CO_2` we get the empirical formula `CH_2`.

This means the compound has a molecular formula of `C_nH_(2n)`, or amounts of `C` and `H` atoms in the ratio 1:2.
So it could be `C_2H_4` (ethene), `C_3H_6` (propene), any other "-ene", or a lot of others (like cyclo-hexane).

Determining the molecular mass (step two) may lead to a molecular formula, which tells us the right number of atoms in the molecule, but still nothing about how they are connected.

Answer 2

The smallest whole number ratio of each element in one atom of a compound.

Explanation:

For example the Empirical formula of Butane (`C_4H_10`) is `C_2H_5`.