A sample of a compound contains 32.0 g C and 8.0 g H. Its molar mass is 30.0 g/mol. What is the compound’s molecular formula?

Convert the sample masses to moles: 32.0 g C ÷ 12.0 g/mol = 2.67 mol C, and 8.0 g H ÷ 1.0 g/mol = 8.0 mol H. Dividing both by 2.67 gives a simplest ratio of C:H = 1:3, so the empirical formula is CH3, with empirical-formula mass 15 g/mol. The molar mass is 30.0 g/mol, twice that value, so the molecular formula is C2H6, choice D.

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