Question

A compound is found to contain 24.8% carbon, 2.0% hydrogen and 73.2% chlorine with a molecular mass of 96.9% g/mol. What is the molecular formula?

Answer 1

Express each percentage as a mass by assuming a 100 gram sample. Then convert to moles and turn the mole ratios into whole numbers which will be the subscripts in the formula.

24.8g C x (1 mol C / 12.0g C) = 2.07 mol C
2.0g H x (1 mol H / 1.01g H) = 2.0 mol H
73.2g Cl x (1 mol Cl / 35.5g Cl) = 2.06 mol Cl

Easy. Since the moles are the same, the mole ratio is 1:1:1 and the empirical formula is CHCl.
The empirical molar mass is 48.5 g/mol
96.9 g/mol / 48.5 = 2

The molecular formula is C2H2Cl2