1. III. Percent Composition

2. A. Percent Composition
In the laboratory, especially when new compounds are made, it is useful to know the composition of a compound in terms of what percentage of the total is each element.

3. B. Percent Comp. Practice
You have 4 oranges and 5 apples. What percent of the total is oranges?

4. C. Fe2O3 vs. FeO Each compound has a different percent composition
Consider Fe2O3 vs. FeO

5. Percent Composition Percent by mass of each element in a compound
Find the molar mass of the compound
Calculate the mass of each element
(ex. Mass of oxygen in CO2 is 2 x 16 g = 32 g)
Divide the mass of each element by the molar mass & multiply by 100%
The formula of carbon dioxide indicates it is composed of one atom of carbon and two atoms of oxygen. Now we will express it in terms of mass percent

6. Calculating Percent Composition Example
What is the percent composition of each element in NH3?
Determine the contribution of each element
Molar mass
On a per mol basis

7. Calculating Percent Composition Example
What is the percent composition of each element in H2O?
Determine the contribution of each element
Molar mass
On a per mol basis