I know the mass of a given substance. I need to convert that mass to moles. What is the conversion factor I need to do that?

Answer 1

You divide the mass of a substance by its molar mass. Molar mass is the atomic weight of an element in grams. For example, the atomic weight of an oxygen atom is approximately 16 AMU. Therefore, the molar mass of an oxygen atom is 16 g/mol. For polyatomic atoms, you add up all the molar masses of the individual atoms.

For example, the molar mass of H2O is 18 g/mol. If you have 36 grams of H2O, you would have 2 mols of the H2O as 36/18 = 2.