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25 g of an unknown hydrocarbon upon burning produces 88 g of CO2 and 9 g of H2O. This unknown hydrocarbon contains: (1) 18 g of carbon and 7 g of hydrogen (2) 20 g of carbon and 5 g of hydrogen (3) 22 g of carbon and 3 g of hydrogen (4) 24 g of carbon and 1 g of hydrogen

1. 18 g of carbon and 7 g of hydrogen
2. 20 g of carbon and 5 g of hydrogen
3. 22 g of carbon and 3 g of hydrogen
4. 24 g of carbon and 1 g of hydrogen

Correct answer: 24 g of carbon and 1 g of hydrogen

Solution

The correct option is right because the total mass of carbon and hydrogen in the hydrocarbon must equal the mass of the hydrocarbon itself, which is 25 g. The combustion products indicate that 24 g of carbon and 1 g of hydrogen is the only combination that satisfies this mass balance.

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