MOLAR MASS
the mass of a mole of any element or compound in grams
The mass of one mole of
carbon atoms
HOW TO CALCULATE THE MOLAR MASS OF A COMPOUND:
1. You need to know how many atoms of each element are in a substance in order to calculate its
molecular weight.
For example, H2O has two atoms of hydrogen and one atom of oxygen.
2. You need to know the molar mass of each element in order to calculate the molar mass of the
compound. You can find these values on your periodic table.
3. Multiply each element's molar mass by how many atoms are present in the formula, and then
add the answers.
To calculate the molar mass of H2O:
Hydrogen: two atoms, molar mass = 1.01g/mol
Oxygen: one atom, molar mass = 16.00 g/mol
(2 x 1.01g) + (1 x 16.00g) = 18.02g/mol
Here’s another example: Calculate the molar mass of Al2(SO4)3:
two atoms of aluminum and the molar mass of Al is 26.98g/mol
three atoms of sulfur and the molar mass of S is 32.07g/mol
twelve atoms of oxygen and the molar mass of O is 16.00g/mol
(2 x 26.98g/mol) + (3 x 32.07g/mol) + (12 x 16.00g/mol) = 342.17g/mol
Calculate the molar mass of:
1) (NH4)2S
2) Fe2O3
3) KClO4
4) SF6
5) (NH4)2SO4