2. Vocabulary Percent Composition -
Tells you the percentage of the mass made up by each element in the compound
Empirical Formula -
Gives the simplest whole number ratio of the atoms of the element
Molecular Formula -
Gives actual number of atoms of each element in the molecular compound

3. Calculating Percent Composition
% of element = mass of element x formula mass compound
Example What is the percent composition of hydrogen and oxygen in water?
Chemical Formula = H2O
Formula mass = 2( g) g = g
% of H = g x g
= 11.2%
% of O = 100 – = 88.8%

4. Example. Find the percent composition of a compound. that contains 2
Example Find the percent composition of a compound that contains 2.30g Na, 1.60g O and 0.100g H .
Total mass = 2.30g g g = 4.00g
% of Na = g x g
= %
% of O = g x g
= %
% of H = g x g
= 2.5 %

5. Example. A sample of an unknown compound with a. mass of 0
Example A sample of an unknown compound with a mass of 0.562g has the following percent compositions: 13.0% C, 2.2% H and 84.8% F. What is the mass of each element?
Formula mass =
% of C = mass C x g
= %
Mass C = g
% of H = mass H x g
= 2.2 %
Mass H = g
% of F = mass F x g
= %
Mass F = 0.477g

6. Vocabulary Percent Composition -
Tells you the percentage of the mass made up by each element in the compound
Empirical Formula -
Gives the simplest whole number ratio of the atoms of the element
Molecular Formula -
Gives actual number of atoms of each element in the molecular compound

7. Calculating Percent Composition
% of element = mass of element x formula mass compound
Example What is the percent composition of hydrogen and oxygen in water?
Chemical Formula = H2O
Formula mass = 2( g) g = g
% of H = g x g
= 11.2%
% of O = 100 – = 88.8%

8. Example. Find the percent composition of a compound. that contains 2
Example Find the percent composition of a compound that contains 2.30g Na, 1.60g O and 0.100g H .
Total mass = 2.30g g g = 4.00g
% of Na = g x g
= %
% of O = g x g
= %
% of H = g x g
= 2.5 %

9. Example. A sample of an unknown compound with a. mass of 0
Example A sample of an unknown compound with a mass of 0.562g has the following percent compositions: 13.0% C, 2.2% H and 84.8% F. What is the mass of each element?
Formula mass =
% of C = mass C x g
= %
Mass C = g
% of H = mass H x g
= 2.2 %
Mass H = g
% of F = mass F x g
= %
Mass F = 0.477g