Acetic acid is the important ingredient in vinegar. It is composed of carbon (40.0%), hydrogen (6.71%) and oxygen (53.29%). Its molar mass is 60.0 g/mol.

Question

What would be the empirical and molecular formulas?

Answer 1

If you assume you have 100 g of sample, then % is the same as grams.

40 g C x 1 mol C/12 g = 3.33 moles C

6.71 g H x 1 mol H/1 g = 6.71 moles H

53.29 g O x 1 mol O/16 g = 3.33 moles O

You can see that the elements are in the ratio of 1C : 2H: 1O

So, empirical formula is CH₂O

The empirical formula has a molar mass of 12 + 2 + 16 = 30 g/mol

Molar mass = 60.0 g so it takes 2 of the empirical formula to make the molecular formula

Molecular formula is C₂H₄O₂