The empirical formula is
21.7 g of potassium is 0.555 mol (
4.44 g of oxygen is 0.2775 mol (
This change to moles is necessary, because we need to compare quantities using a unit that refers to a number of atoms rather than a total mass.
Now, look for a whole-number ratio between these two values. If it is not obvious, try dividing both by the smaller. This will give you a ratio in which one term is a one, and should be easier to recognize.
So, the ratio in the compound is 2 atoms of K for each 1 atom of O, giving a formula
The empirical formula is the simplest whole number ratio that represents constituent atoms in a species. Given masses of constituent atoms, we simply divide thru by the atomic mass:
And if I divide thru by