Combustion analysis of an unknown hydrocarbon produced the following results: C 60.00%, H 4.48%, O 35.52%. Determine the empirical formula. A) C₉H₉O₅ B) C₉H₈O₃ C) C₈H₉O₄ D) C₉H₈O₄ E) C₈H₈O₄

Question

Quizplus · Accepted Answer

Assume a 100 g sample of the unknown hydrocarbon. Then it contains 60 g C, 4.48 g H, and 35.52 g O.
The number of moles of each element is found by dividing by its molar mass: 
- C: 60 g / 12.01 g/mol = 4.998 moles
- H: 4.48 g / 1.008 g/mol = 4.444 moles
- O: 35.52 g / 16.00 g/mol = 2.220 moles
Dividing each by the smallest, we get the empirical formula: 
- C: 4.998 / 2.220 ≈ 2.25 → 2
- H: 4.444 / 2.220 ≈ 2.00 → 2
- O: 2.220 / 2.220 = 1
Therefore, the empirical formula is C2H2O. The only choice that matches this formula is D.

Combustion Analysis of an Unknown Hydrocarbon Produced the Following Results