Percentage composition is the percentage of a formula mass represented by each element.

Percentage composition compares the mass of one part of a substance to the mass of the whole.

Calculating percentage composition:

1. Do a formula mass calculation.
    
2. Divide the total atomic mass for each element by the total formula mass of the compound.

Sample problem: Calculate the percentage composition of C₂H₅OH Because of rounding mass numbers to whole numbers, the total % could be between 99 and 101. If it is outside that range, you probably have a mistake.

 
Percentage Composition

Percentage Composition Assignment

Bubble Gum

Percentage Composition