Question

What is the `"empirical formula"`?

Answer 1

The empirical formula is the simplest whole number ratio that defines constituent atoms in a species. The molecular formula is always a multiple of the empirical formula.

Explanation:

Ordinarily you have to determine the empirical formula experimentally, (that's what `"empirical means"`, `"experimental"`), and from this empirical formula, the molecular formula is calculated. I will give you a few examples with this order reversed. The molecular formula of hydrogen peroxide is `H_2O_2`; its empirical formula is `OH`. The molecular formula of butane is `C_4H_10`; its empirical formula is `C_2H_5.` In both instances the empirical formula is the simplest whole number ratio that defines the proportion of the constituent atoms, as required. What are the empirical formulae of ethane, `C_2H_6`, hexane, `C_6H_14`, octane, `C_8H_18`, and ethanol, `C_2H_5OH`?

There are many other answers on Socratic that show how the empirical formula may be calculated by means of a protocol with specific problems quoted and solved. I urge you to search them out.