6.6 THE COMPOSITION
OF UNKNOWN
COMPOUNDS
PERCENTAGE COMPOSITION
- defined as the percentage, by mass, of each
element in a compound
In a 2.0g sample of a hydrocarbon, the mass of
the carbon was determined to be 0.801g.
What percentage of the hydrocarbon is carbon?
PERCENTAGE COMPOSITION
If you calculated the percent composition of a
4.0g sample, what would be your answer?
This is known as
THE LAW OF DEFINITE PROPORTIONS!
To calculate percent
composition, use the
following formula:
% element =
melement
m samplex 100%
EXAMPLE 1: A 500.00mg tablet of Aspirin, C9H8O4
contains 300mg carbon and 8.08mg hydrogen.
The remaining mass is oxygen. Determine its
percent composition.
LET'S TAKE THIS A STEP
FURTHER...
Let's try to calculate percentage composition from a
chemical formula.
EXAMPLE 2: Determine the percentage
composition of calcium hydroxide, Ca(OH)2
Learning check
1. What is the percentage composition of (NH4)3PO4
N: 28%
H: 8%
O: 43%
P: 21%
HOMEWORK:
Mole Airlines
-due Wednesday
Finish the Problem
Set