Assume we have a sample of zinc chloride and determine the masses of Zn and Cl present. Let's say we find that the sample contains 1 gram of Zn and 1.33 grams of Cl.
Convert the masses to moles using their respective atomic masses:
Moles of Zn = 1 g / 65.38 g/mol (atomic mass of Zn) ≈ 0.0153 mol
Moles of Cl = 1.33 g / 35.45 g/mol (atomic mass of Cl) ≈ 0.0375 mol
Divide the moles of each element by the smaller number of moles to obtain the simplest whole number ratio:
0.0153 mol Zn / 0.0153 mol ≈ 1
0.0375 mol Cl / 0.0153 mol ≈ 2.45
To get whole numbers, multiply the ratio by a suitable factor (in this case, 2):
2 × 1 ≈ 2
2 × 2.45 ≈ 5
The empirical formula for zinc chloride is therefore ZnCl2. This formula indicates that for every 1 zinc atom, there are 2 chlorine atoms in the compound.
