Chemistry : Percentage Composition of Chemical Compounds

How to Calculate the Percentage Composition of a Chemical Compound?

Example:
What is the percentage of the various elements in Sodium Carbonate [Na₂CO₃] ?
Given Atomic Weights: C = 12 ; O = 16 ; Na = 23

The first step is to calculate the Molecular Weight (or the Formula Weight) of the chemical compound by adding the atomic weights of the atoms (elements) that constitute the compound.

Molecular weight of Na₂CO₃
= (2 x Atomic weight of Na) + Atomic weight of C + (3 x Atomic weight of O)
= (2 x 23) + 12 + (3 x 16)
= 46 + 12 + 48 = 106

Now, 106 grams of Sodium Carbonate [Na₂CO₃] contain 46 grams of Sodium [Na], 12 grams of Carbon [C], and 48 grams of Oxygen [O].

So,
Percentage of Sodium [Na] in Sodium Carbonate [Na₂CO₃] = 46/106 x 100 = 43.40%.
Percentage of Carbon [C] in Sodium Carbonate [Na₂CO₃] = 12/106 x 100 = 11.32%.
Percentage of Oxygen [O] in Sodium Carbonate [Na₂CO₃] = 48/106 x 100 = 45.28%.

Practice Exercise for Chemistry Module on Percentage Composition of Chemical Compounds