Exam Style Question - 1

Question: A hydrocarbon contains 85.7% carbon and 14.3% hydrogen by mass. Its M_r is 56.0. Find its empirical and molecular formulae.Step 1: divide by A_r. C: 85.7 / 12.0 = 7.14. H: 14.3 / 1.0 = 14.3.Step 2: divide by the smallest value. C: 7.14 / 7.14 = 1. H: 14.3 / 7.14 = 2. The empirical formula is CH₂.Step 3: empirical formula mass = 12.0 + 2.0 = 14.0. 56.0 / 14.0 = 4.Step 4: molecular formula = 4 × CH₂ = C₄H₈. This fits the general formula C_nH_2n, so the compound could be an alkene such as but-1-ene or a cycloalkane.