How can you determine formula mass?

Sep 28, 2016

You sum the atomic masses of the elements making up the compound.

Explanation:

The formula mass is the sum of the atomic masses of the elements making up the compound. For example, sulphuric acid, ${H}_{2} S {O}_{4}$.

Atomic mass of hydrogen (H) - 1.00794 g/mol
Atomic mass of sulphur (S) - 32.065 g/mol
Atomic mass of oxygen (O) - 15.9994 g/mol

So, the formula mass is:

(2 x 1.00794) + 32.065 + (4 x 15.9994) = 98.079 g/mol

This video discusses two additional examples; silicon dioxide and magnesium hydroxide.

Hope this helps!