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On complete combustion, a gaseous hydrocarbon produces 0.72 g of water and 3.08 g of carbon dioxide. What is the empirical formula of this hydrocarbon?

1. C2H4
2. C3H4
3. C6H5
4. C7H8

Correct answer: C7H8

Solution

CO2 3.08/44 = 0.07 mol C; H2O 0.72/18 = 0.04 mol -> 0.08 mol H. C:H = 0.07:0.08 = 7:8 -> C7H8. Stored C3H4 is wrong.

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