1. Percentage Composition

2. Percent Part X 100% Whole Percent by mass = Mass of element X 100%
Mass of compound

3. Percent Composition of H2O
2 H’s = 2 (1g) = 2g
1 O = 1 (16g) = 16g
______
18g/mole (molar mass)

4. Percent Composition % H = 2g x 100% = 11.11% 18g
% O = 16.0g x 100% = 88.89%
18.0g _______
100.00%

5. Percent Composition of C6H12O6
6 C = 6 (12g) = 72g
12 H = 12 (1g) = 12g
6 O = 6 (16g) = 96g
______
180g/mole

6. % C =
% H =
% O =
72g x 100% = 40.00%
180g
12g x 100% = %
180g
96g X 100% = %
180g _______
100.00%

7. Percentage Composition
Sum of individual element %’s must add up to exactly 100%
usually works out exact if round to 2 decimal places