A certain sugar has a chemical composition of 40 % carbon, 6.6 % hydrogen, and 53.3 percent oxygen. The molar mass is 180 g/mol. What is the molecular formula?
We assume 100 g of unknown. In such quantity there are:
Note that I divide thru by the ATOMIC masses of each component.
I gets the ratio:
Now it is a fact that while the empirical formula may NOT be the same as the molecular formula, the molecular formula is ALWAYS a multiple of the empirical formula.
Normally, you would not be given the percentage composition of oxygen (because oxygen content can rarely be measured!). A more advanced question would have given percentage compositions of