Question

The percentage composition of sodium phosphate, as determined by analysis is: 42.1% of sodium, 18.9% of phosphorus and 39% of oxygen. Find the empirical formula of the compound (work to two decimal places). [H = 1, N = 14, O = 16, Na = 23, P = 31, Cl = 35.5, Pt = 195]

Answer 1

Element	Atomic mass	Percentage	Relative number of moles	Simplest mole ratio	Whole number ratio
Na	23	42.1	$\frac{42.1}{23}=1.83$	$\frac{1.83}{0.61}=3$	3
P	31	18.9	$\frac{18.9}{31}=0.61$	$\frac{0.61}{0.61}=1$	1
O	16	39	$\frac{39}{16}=2.44$	$\frac{2.44}{0.61}=4$	4

Empirical formula of the compound is Na₃PO₄.