1. Created by: Miss K. Marshall
Percent Composition
Created by: Miss K. Marshall

2. Percent Composition of a Compound

3. Percent from mass data
When a 13.60g sample of a compound containing only magnesium and oxygen is decomposed, 5.40g of oxygen is obtained. What is the percent composition of this compound?
Answer: %Mg = 60.3% %O = 39.7%

4. Percent from mass data
A compound is formed when 9.03 g of Mg combines completely with 3.48 g of N. What is the percent composition of this compound?
Answer: %Mg = %N = 27.8

5. Percent Composition from the Chemical Formula

6. Percent Composition from the Chemical Formula
Propane, (C3H8), the fuel commonly used in gas grills, is one of the lighter compounds obtained from petroleum. Calculate the percent composition of propane.
Answer: %C = 81.8% %H = 18%

7. Percent Composition from the Chemical Formula
Calculate the percent nitrogen in these common fertilizers.
a. NH3 
Answer: 82.4%
b. NH4NO3
Answer: 35.0%

8. Percent Composition as a conversion factor
We can use the % comp. to calculate the number of grams of any element in a specific mass of a compound
Multiply the mass of the compound by a conversion factor based on the percent composition of the element in the compound

9. Percent Composition as a Conversion Factor
Using an earlier sample problem containing propane, we found that a 100g sample of propane would contain 81.8g of Carbon and 18 g of hydrogen. The ratio would be 81.8g C/100g propane. We can use this ratio to determine how much carbon is in 82.0g of propane.
Answer: 67.1 g C