To perform calculations based on moles and mass, you need to use the concept of molar mass. Molar mass is the mass of one mole of a substance and is expressed in grams per mole (g/mol).

Here are some common calculations you can perform using moles and mass:

1. Calculating moles from mass:
   • Moles = Mass / Molar mass
2. Calculating mass from moles:
   • Mass = Moles x Molar mass
3. Calculating the molar mass of a compound:
   • Molar mass = Sum of the atomic masses of all the atoms in the compound
4. Calculating the percent composition of an element in a compound:
   • Percent composition = (Mass of element / Molar mass of compound) x 100
5. Calculating the empirical formula from percent composition:
   • Convert the percent composition to grams.
   • Convert grams to moles.
   • Divide each mole value by the smallest mole value obtained.
   • Round the resulting values to the nearest whole number to obtain the empirical formula.
6. Calculating the molecular formula from the empirical formula:
   • Determine the molar mass of the empirical formula.
   • Divide the molar mass of the compound by the molar mass of the empirical formula.
   • Multiply the subscripts in the empirical formula by the resulting value to obtain the molecular formula.

These calculations are commonly used in stoichiometry, which involves the quantitative relationships between reactants and products in chemical reactions.