Question

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?
CH3
CH4
C2H4
C2H6

Answer 1

Find moles from the masses: n(C)=32.0/12.01≈2.66, n(H)=8.0/1.008≈7.94.
Ratio n(H)/n(C)≈7.94/2.66≈3 → empirical formula CH3 (empirical mass = 15.0 g/mol).
Molecular mass 30.0/15.0 = 2, so molecular formula = 2 × CH3 = C2H6.

Answer: C2H6.