Question

A compound has the empirical formula CH2O and a gram-formula mass of 60. grams per mole. What is the molecular formula of this compound?
(1) CH2O (3) C3H8O
(2) C2H4O2 (4) C4H8O4

Answer 1

We already know the molar mass of C is 12.01g/mol, of H is 1.008 g/mol, and of O is 16g/mol.

If the molecular formula were also the empirical formula (which is CH2O), then it would have a molar mass of:
12.01g/mol +2*(1.008g/mol)+ 16g/mol= 30.03g/mol

However, the actual molar mass of the molecular formula is 60.g/mol, which is about twice as large as 30.03g/mol. Therefore, we have to multiply the empirical formula by 2.

The molecular formula of this compound is (2) C2H4O2.

Hope this would help~