Finding the emprical formula
From the formula of a compound you can tell what masses of the elements combine. But you can also do things the other way round. If you know what masses combine, you can work out the formula.
These are the steps:
Find the masses that combine (in grams) by experiment.
Change grams to moles of atoms
This tells you the ratio in which atoms combine.
So you can write a formula
A formula found in this way is called the empirical formula. The empirical formula shows the simplest ration in which atoms combine.
Example: 32grams of sulfur combine with 32 grams of oxygen to form an oxide of sulfur. What is its empirical formula?
Elements that combine
Masses that combine
Relative atomic masses (Ar)
Moles of atoms that combine
Ratio in which atoms combine
Empirical formula
sulfur oxygen
32g 32g
32 16
32/32=1 32/16=2
1:2
SO2
So the empirical formula of the oxide that forms is SO2