3. Since you assumed mass of one mole of cpd, the moles should be close enough to whole to assume they are whole. So you do not have change to a molar ratio or multiple by a common number.
Step to Calculate Molecular Formula (MF) from Empirical Formula (EF)
As you know, molecular formula are really a certain number of "empirical formula" units. An analogue is a chain with several links. The chain is made up of several identical links so if you know the mass of the chain and the mass of a single link, then you can determine how many links there are in the chain. Similarly, the MF is made up of a certain number of EF units. Therefore, if you know the mass of the molecular formula (we call molar mass) and mass of a mole of the EF, if you divide the two, you get how many EF units there are in the MF.
1. Determine the molar mass of the EF (you have to be given this or given the chemical formula of the EF).
2. Must be given the molar mass of the MF.
3. Divide the molar mass of the EF into the molar mass of the MF or
MM of MF = # of EF units in MF
MM of EF
4. Then multiple the subscripts in the EF with the # of EF in the MF to determine the correct subscript for the chemical formula for the MF.