3 From empirical to molecular formula

n = molar mass of the compound / molar mass of the empirical formula

Molecular formula = (empirical formula)ₙ.

Worked example 5.6. Compound X: empirical formula CH₂ (mass 14), molar mass 28 → n = 2 → C₂H₄.

Worked example 5.7 — hydrocarbon from carbon percentage (pattern). A hydrocarbon has 82.76 % carbon and a molar mass of 58 g/mol. [C = 12, H = 1] H % = 17.24. C: 6.897; H: 17.24; ratio H/C = 2.5 → ×2 → C₂H₅ (mass 29); n = 58/29 = 2 → C₄H₁₀.