A 9.10 g sample of a compound contains 5.81 g of iron, Fe, 1.07 g of phosphorus, P, and oxygen, O. Calculate the empirical formula for the compound.

Answer 1

First, let's find the mass of O in the sample.

Total mass = mass Fe + mass P + mass O

9.10 g = 5.81 g + 1.07 g + x g

x = 2.22 g O

Now, convert g of each element to moles:

moles Fe = 5.81 g Fe x 1 mol Fe / 55.85 g = 0.104 mols Fe

moles P = 1.07 g P x 1 mol P / 30.97 g = 0.0345 mols P

moles O = 2.22 g O x 1 mol O / 16 g = 0.139 mols O

Divide all by 0.0345 to try to get whole numbers...

0.104 mol Fe / 0.0345 = 3.0 mol Fe

0.0345 mol P / 0..0345 = 1.0 mol P

0.139 mol O / 0.0345 = 4.0 mol O

Empirical formula = Fe₃PO₄