Final answer:
The empirical formula mass is the sum of atomic masses in the compound's simplest ratio, while the molar mass is the mass of one mole of the compound. To find the molecular formula from the empirical formula, divide the molar mass by the empirical formula mass. For ionic compounds, the term formula mass is used instead of molecular mass.
Step-by-step explanation:
Difference Between Molar Mass and Empirical Formula Mass
The distinction between molar mass and empirical formula mass of a compound is fundamental in chemistry. The empirical formula mass refers to the sum of the atomic masses of all atoms in the empirical formula, which represents the simplest whole-number ratio of elements in a compound. In contrast, molar mass refers to the mass of one mole of a substance and is measured in grams per mole (g/mol). It indicates the mass of the actual number of atoms present in a molecule of the compound.
To determine a compound's molecular formula from its empirical formula, we first need to know the compound's molar mass. By dividing the molar mass by the empirical formula mass, we can find the integer multiple, denoted as n, which represents the number of empirical formula units in a molecule of the compound.
For example, the empirical formula of benzene is CH with an empirical formula mass of approximately 13 g/mol (12 for carbon plus 1 for hydrogen). However, the molar mass of benzene is approximately 78 g/mol. To find 'n', we divide 78 g/mol by 13 g/mol to get 6, which tells us that the molecular formula is C6H6.
In the case of ionic compounds, which do not have molecules per se, we use the term formula mass instead of molecular mass. It is important to note that empirical formulas can be determined from the percent composition of a compound using mass spectrometry to help in finding the molar mass.