1. Percent Composition by Mass

2. Percent Composition by Mass
Ex.(1) Calculate the percent composition (by mass to the tenth’s place) of chlorine in the compound MgCl2.
% comp = mass of part  100
mass of whole
X =
X =
71.0 g
 100
95.3 g
74.5%

3. Percent Composition by Mass
Ex.(2) Calculate the percent composition (by mass to the tenth’s place) of carbon in the compound C6H12O6.
% comp = mass of part  100
mass of whole
X =
X =
72.0 g
 100
180.0 g
40.0%

4. Percent Composition by Mass
Ex.(3) Calculate the percent composition (by mass to the tenth’s place) of oxygen in the compound CO2.
% comp = mass of part  100
mass of whole
X =
X =
32.0 g
 100
44.0 g
72.7%

5. Percent Composition by Mass
Ex.(4) Calculate the percent composition (by mass to the tenth’s place) of potassium in the compound KOH.
% comp = mass of part  100
mass of whole
X =
X =
39.1 g
 100
56.1 g
69.7%

6. Percent Composition by Mass
Ex.(5) Calculate the percent composition (by mass to the tenth’s place) of hydrogen in the compound HCl.
% comp = mass of part  100
mass of whole
X =
X =
1.0 g
 100
36.5 g
2.7%

7. Percent Composition by Mass
Compounds which contain a salt and water combined in definite proportions are known as hydrates.
CaSO42H2O is commonly known as gypsum and is used to make wallboard or chalk.

8. Percent Composition by Mass
Notice that a hydrates formula contains a “dot” between the salt and the water.
BaCl22H2O NiF24H2O
This “dot” is NOT a multiplication symbol.
The “dot” simply indicates that the water molecules are bonded to the salt’s metal atom.

9. Percent Composition by Mass
Ex.(6) Calculate the percent of water in the hydrate – BaCl22H2O?
% comp = mass of part  100
mass of whole
X =
X =
36.0 g
 100
244.3 g
14.7%

10. Percent Composition by Mass
Ex.(7) Calculate the percent of water in the hydrate – NiF24H2O?
% comp = mass of part  100
mass of whole
X =
X =
72.0 g
 100
168.7 g
42.7%