1. Percent Composition
Chapter 7-3, p

2. Formula Mass Defined as:
the sum of the average atomic masses of all the atoms represented in the chemical formula of a molecule, ionic compound or ion.
***This is the same as the molar mass you learned to compute in Chapter 3!

3. Example CO2 = carbon dioxide 1 C = 1(12.01 g/mol) = 12.01 g/mol
2 O = 2(16.00 g/mol) = g/mol
Total formula mass = g/mol

4. Example KClO3 = potassium chlorate 1 K = 1(39.10 g/mol) = 39.10 g/mol
1 Cl = 1(35.45 g/mol)= g/mol
3 O = 3(16.00 g/mol) = g/mol
Total formula mass = g/mol

5. Example (NH4)2SO3 = ammonium sulfite
2 N = 2(14.01 g/mol) = g/mol
8 H = 8(1.01 g/mol) = g/mol
1 S = 1(32.07 g/mol) = g/mol
3 O = 3(16.00 g/mol) = g/mol
Total formula mass = g/mol

6. Percent Composition Defined as:
the percentage by mass of each element in a chemical compound
For example, the amount of oxygen contained in one unit of NaOH by mass is 32.6%
So we would state that NaOH is 32.6% oxygen; this is the percent composition of oxygen in NaOH

7. Example CO2 = carbon dioxide 1 C = 1(12.01 g/mol) = 12.01 g/mol
2 O = 2(16.00 g/mol) = g/mol
Total formula mass = g/mol
Now find the percent composition of oxygen… take the mass and divide by the total, times 100%…
32.00/44.01 g/mol X 100% = 72.71%

8. Example KClO3 = potassium chlorate 1 K = 1(39.10 g/mol) = 39.10 g/mol
1 Cl = 1(35.45 g/mol)= g/mol
3 O = 3(16.00 g/mol) = g/mol
Total formula mass = g/mol
Now find the percent composition of oxygen… take the mass and divide by the total, times 100%…
48.00/ g/mol X 100% = 39.17%

9. Example (NH4)2SO3 = ammonium sulfite
2 N = 2(14.01 g/mol) = g/mol
8 H = 8(1.01 g/mol) = g/mol
1 S = 1(32.07 g/mol) = g/mol
3 O = 3(16.00 g/mol) = g/mol
Total formula mass = g/mol
Now find the percent composition of oxygen… take the mass and divide by the total, times 100%…
48.00/ g/mol X 100% = 41.32%

10. You Try It! Percent composition of P and Br in PBr5 P=7.19%; Br=92.81%
Percent composition of Ag and O in Ag2O
Ag=93.10%; O=6.90%
Percent composition of C, H, and O in C6H12O6
C=39.99%; H=6.73%; O=53.28%
What is the percent composition of sugar in a piece of bubble gum?