Answer the following question given this paragraph: 

Empirical formulas can be determined from the percent composition of a compound. In order to determine its molecular formula, it is necessary to know the molar mass of the compound. Chemists use an instrument called a mass spectrometer to determine the molar mass of compounds. In order to go from the empirical formula to the molecular formula, follow these steps:.


Q: In order to determine its molecular formula, it is necessary to know what about the compound?


A:
molar mass