Question

the empirical formula of a compound is CH3O. What is the molecular formula if the mass is 62.0g/mole?

Answer 1

The empirical formula is the simplest number of atoms each can be reduced to. If we want to find the molecular formula, we need to find the right number of atoms of each that will add to the given mass, in this case, 62.0 grams. In this case, we find the individual masses of each element.
Carbon: 12.011 grams

Hydrogen: 1.008 grams * 3 since there are three

Oxygen: 15.999 grams

When we add these, we get a total mass of 31.034 grams. If we multiply it by two, we get the exact mass of the molecule formula, 62.068. Since we multiplied by two, all molecules have to be multiplied by two. That just means we multiply the number of molecules in the compound by two.
Therefore,

Empirical: CH3O

CH3O*2= C2H6O2 = Molecular