The gram formula mass of a compound is the amount of that compound that has the same mass in grams as the formula mass in atomic mass unit. An atom of each element has a characteristic mass and in like manner each molecule of a compound has a characteristic formula mass.
When the formula mass of an ionic compound is determined by the addition of its component atomic masses and expressed in grams, it is called the Gram Formula Mass.
Gram Formula Mass is mathematically expressed as
The gram formula mass of a substance is the sum of the atomic masses of all atoms is a formula unit of the compound, whether molecular or not.
Gram Formula Mass Problems
Solved problems based on gram formula mass are given below.
1 K = 39
1 Al = 27
2(SO4) = 192 = 2(32 + 16 $\times$ 4)
12 H2O = 216 = 12(2 + 16)
Therefore the gram formula mass is
1 mol = 474g
1 Ca = 40
1 C = 12
3 O = 48 = 3 $\times$ 16
Therefore the gram formula mass of CaCO3 is
CaCO3 = 100 formula mass
CaCO3 = 100g = gram formula weight.