Percentage compositionIndicates the relative amount of each element

present in a compound.

Calculating percentage compositionStep 1 : Calculate molar mass

Step 2 : Divide the subtotal for each element’s mass by the molar mass.

Step 3: Multiply by 100 to convert to a percentage.

Example 11. Calculate the molar mass of water, H2O.

Step 1 – H- 2(1.01)= 2.02 O – 1(16.0)= 16.0 ________ 18.02

Step 2 2.02/18.02 X 100 = 11.21%

16.0 /18.02 X 100 = 88.79 %

Water is composed of 11.21 % hydrogen and 88.79 % oxygen.

Example 2

Calculate the percentage composition of sucrose , C12H22O11.

Example 3Find the percentage composition of hydrogen

in sulfuric acid.