1. Percent Composition Vocabulary Percent Percent Composition “No. 5”
Mark Rothko
Russian
1960

2. prior knowledge
How could you calculate what percentage of the painting is red, what percentage is black, and what percentage is green?

3. General Formula for Percent

4. Percent Composition
Chemists often need to know the percentage of each element in a compound by mass. This is called percent composition.

5. Example 1
To the right are pictures of copper(II) chloride, CuCl2. If a 34.2 g sample of copper(II) chloride contains 16.2 g of copper and 18.0 g of chlorine, what is the percent composition of CuCl2?

6. Example 1 Continued
First, determine the percent of copper in the compound:
Next, determine the percent of chlorine in the compound:

7. LiNO3 Example 2 What is the percent composition of lithium nitrate?
First we need its formula:
LiNO3
Notice we don’t have any masses in this problem. Any ideas on what we can use to solve for the percent composition?

8. Example 2 Continued
We’ll use the molar masses of everything rather than the mass! Li: 6.94 g/mol N: g/mol O: g/mol LiNO3: g/mol

9. Example 2 Continued
100.0%

10. Time to Practice on your Own!!!