How Do You Calculate Molar Mass?

Calculate the molar mass of a compound by using the chemical formula of the substance and the atomic weight for each type of atom in the substance. For example, the molar mass of sodium carbonate is 106 grams per mole.

  1. Determine the chemical formula

    Write the chemical formula for sodium carbonate as Na2CO3. That means sodium carbonate has sodium, carbon and oxygen atoms arranged in particular ways to create the molecular compound.

  2. Identify the number of atoms in each molecule

    Use the chemical formula to determine how many atoms of each substance are in the molecule. There are two sodium atoms, one carbon atom and three oxygen atoms per molecule of sodium carbonate.

  3. Plug in atomic weights

    Use the periodic table of elements to find the atomic weights of sodium, carbon and oxygen to calculate molar mass. Sodium has an atomic weight of 23 grams per mole, and sodium carbonate has two atoms of sodium for 46 grams per mole. Carbon has 12 grams per mole, and oxygen weighs 16 grams for one mole, or 48 grams per mole in sodium carbonate.

  4. Add the weights together

    Combine the calculated masses of each component of the molecule to determine the mass of the molecule. The mass of sodium carbonate weighs 106 grams for one mole. One mole equals 6.022x10^23 atoms of a particular substance. Heavier atoms weigh more for the same amount of atoms, whereas lighter atoms weight less.