A certain compound is composed only of 0.065 mol of carbon, C, and 0.195 mol of hydrogen, H. The compound is known to have a molar mass of 90.0 g/mol.

Question

Determine the empirical and molecular formula of the compound.

Answer 1

To get the empirical formula, we want to convert all the elements to moles and then get them to be whole numbers. We are actually given the moles, so we don't have to calculate them.

moles C = 0.065 mol

moles H = 0.195 mol

To get whole numbers, divide both by 0.065

moles C = 0.065 / 0.065 = 1

moles H = 0.195 / 0.065 = 3

Empirical formula = CH₃

Molar mass of empirical formula = 12 + 3 = 15 g/mol

Molecular formula has a molar mass of 90.0 g /mol

90.0 / 15 = 6 empirical formulae in 1 molecular formula

So molecular formula is...

C₆H₁₈