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In an organic compound of formula CxHyOz, the mass percentages of carbon and hydrogen are in the ratio 6:1. Also, a single molecule of this compound contains only half the oxygen needed for complete combustion of one molecule of CxHy to carbon dioxide and water. What is the empirical formula of the compound?

1. C3H6O3
2. C2H4O
3. C3H4O2
4. C2H4O3

Correct answer: C2H4O3

Solution

12x/y = 6 gives y = 2x, so the hydrocarbon part is CxH2x. Complete combustion needs 3x O atoms (2x for CO2 + x for H2O); half of that is 1.5x, so z = 1.5x. With x = 2 the empirical formula is C2H4O3.

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