Question

An oxide of phosphorus contains 56.4% phosphorus and 43.6% oxygen. It's relative molecular mass is 220. Find both the empirical and the molecular formula of the oxide'

Answer 1

moles of P = 56,4g/30,974g/mole = 1,82 moles P
moles of O = 43,6 /15,999 = 2,73 moles of O

Converting to the simplest ratio:

For P: 1,82/1, 82 =1
For O: 2,73/1,82 = 1,5

which I guess approximates
1 P and 2 Oxygens.
PO2 -> the empirical formula

I suppose this is how it's done, but Im not quite sure.