Question

A sample of a compound contains 60.0 g C and 5.05 g H. Its molar mass is 78.12 g/mol. What is the compound’s molecular formula?
CH
C2H2
C6H6
C6H

Answer 1

1) Convert masses to moles (assume sample contains only C and H):
- moles C = 60.0 g / 12.01 g·mol−1 = 4.996 mol
- moles H = 5.05 g / 1.008 g·mol−1 = 5.01 mol

2) Ratio C:H ≈ 4.996 : 5.01 ≈ 1 : 1 → empirical formula = CH.
Empirical formula mass = 12.01 + 1.008 = 13.02 g·mol−1.

3) Molecular formula factor = Molar mass / empirical mass = 78.12 / 13.02 ≈ 6.
Multiply empirical formula by 6 → C6H6.

Answer: C6H6.