43.64g P x (1 mol P / 30.974g P) = 1.409 mol P

56.36 g O x (1 mol O / 15.999g O) = 3.523 mol O
So since we chose 100.00 g of compound we have  43.64g P & 56.36 g O.
2nd Step:  Convert grams to moles.
Can we compare grams directly?
A white compound is analyzed and found to contain
43.64% phosphorous and 56.36% oxygen by mass.
Empirical Formula Example 1