1. Chemical Quantities Percent Composition
The label on a bag of fertilizer states the percentages of N, P, and K
How do they know that?

2. Percent Composition
Is the percent by mass of each element in a formula
First… Figure out the total mass of each element to get the Formula Mass
Second… Divide the Mass of the particular element by the total Formula Mass
Third… Multiply that number by 100 to get percent!

3. Example: Calculate the percent composition of Carbon in CO2
First… Figure out the total mass of each element to get the Formula Mass: CO2 = 1C (12.01g) + 2 O(16.00 g) = g/mol Second…Divide the Mass of the particular element by the total Formula Mass g C = g CO2 Third…Multiply the amount by 100 to get a percent! x 100 = 27.29% Carbon in CO2

4. Example: Calculate the percent composition of Oxygen in CO2
First… Figure out the total mass of each element to get the Formula Mass:
CO2 = 1C (12.01g) + 2 O(16.00 g) = g/mol
Second…Divide the Mass of the particular element by the total Formula Mass
32.00 g O = 72.71
44.01 g CO2
Third…Multiply the amount by 100 to get a percent!
x = % Oxygen in CO2

5. Check your answers… Add up your percentages They MUST add up to 100!
Carbon = +
Oxygen =
Total =

6. Learning Check
What is the percent composition of lactic acid, C3H6O3, a compound that appears in the blood after vigorous activity?

7. Learning Check 1) 7.102 %C 2) 35.51 %C 3) 64.58 %C
The chemical isoamyl acetate C7H14O2 gives the odor of pears. What is the percent of carbon in isoamyl acetate?
1) %C
2) %C
3) %C