1) divide each percentage by the relative atomic mass of the element
2) divide all results by the smallest number
3)multiply by a whole number to get the simplest whole number ratio (if necessary)
that is to say:
Na S O
32.37÷23 22.58÷32 45.05÷16
= 1.407 = 0.7056 = 2.816 (to 4 significant figures)
the smallest number here is 0.7056 so:
1.407÷0.7056 0.7056÷0.7056 2.816÷0.7056
=1.99 approx.2 = 1 3.99 approx. 4
here there is no need to carry out step 3 as ratio obtained is already a simplest whole number ratio
so empirical formula is: Na₂SO₄