Explain how to determine the molecular formula of a compound?

Example

An unknown compound contains 85.63 % C and 14.37 % H. Its experimental molar mass is 56 g/mol. What is its molecular formula?

Solution

Assume we have 100 g of the compound. Then we have 85.63 g of C and 14.37 g of H.

Moles of C=85.63g C×1 mol C12.01g C=7.130 mol C

Moles of H=14.37g H×1 mol H1.008g H=14.26 mol H

Moles of CMoles of H=7.130mol14.26mol=12.000≈12

The empirical formula is CH2.