Determine the molecular formula of a hydrocarbon that contains 81.8% carbon, 18.2% hydrogen
| February 5, 2021 | education
Determine the molecular formula of a hydrocarbon that contains 81.8% carbon, 18.2% hydrogen and has a hydrogen density of 15.
The hydrogen density DH2 shows how many times the desired hydrocarbon is heavier than hydrogen gas H2.
The relative molecular weight of hydrogen Mr (H2) = 2 × Ar (H) = 2 × 1 = 2.
The relative molecular weight of the hydrocarbon Mr (CxHy) = DH2 × Mr (H2) = 15 × 2 = 30.
The mass of carbon in the desired substance m (C) = Mr (CxHy) × 81.8%: 100% = 30 × 81.8%: 100% = 24.
Since Ar (C) = 12, the number of carbon atoms is 24: 12 = 2.
Mass of hydrogen m (H) = Mr (CxHy) × 18.2%: 100% = 30 × 18.2%: 100% = 6.
Since Ar (H) = 1, the number of hydrogen atoms is 6: 1 = 6.
Answer: C2H6.
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