1. To find a percent: part X 100
Percent Composition
To find a percent: part X 100
whole
1) Find the mass of each element in the compound and multiply masses by subscripts. (Find molar mass)
2) Divide by the total mass of the compound
3) Multiply by 100 to get percent
Total mass of element X 100
Total mass of compound

2. Example 1 What percent of copper is in the compound Cu2S?
Cu=2 x 63.55= 127.1
S= 1 x 32.07= 32.07 g
127.1 g x 100= % Cu

3. Example 2 What percent of each element is in barium phosphate?
HINT: YOU HAVE TO WRITE THE FORMULA FIRST!!!
Remember the percentage should add up to 100

4. Example 2 Ba+2 PO4 -3 Ba3(PO4)2 write formula first
Ba=3 x =
P= 2 x =
O= 8 x = g
x 100= 68.4% Mg x 100 = 10.3% P
x 100 =21.3% O

5. Try these on your own Find the percent for all elements
CuBr2
NaOH
(NH4)2S
N2S2
KMnO4