How to Find the Gram Formula Mass of an element
The mass of one mole of a substance is also called the “Gram Formula Mass”. Here’s
how to calculate it for an element.
e.g. Lithium
Lithium is not one of the diatomic elements so the gram formula mass is simply the
number on p4 of the data book expressed in grams.
Lithium, Li, 7 g
e.g. Oxygen
Oxygen is a diatomic (two atoms) element so the gram formula mass is the number on
p4 of the data book multiplied by 2 and expressed in grams.
Oxygen, O2, 16 x 2 = 32 g
How to Calculate a Gram Formula Mass of a compound
The mass of one mole of a substance is also called the “Gram Formula Mass”. Here’s
how to calculate it for a compound.
e.g. Magnesium chloride
1) Work out the formula of the compound/element
2) Find the relative atomic mass of each element (p4 of the data book).
3) Multiply the relative atomic masses by the subscripts
4) Add the answers together. The answer (expressed in grams) is the gram
formula mass