Chemistry 2015
Molar Mass and Percent Composition
Name_____________________
Molar Masses:
Explain how you find the molar mass of an element or compound.
Add the atomic masses
One mole of anything has 6.02 X 1023 particles/pieces.
This is called Avogadro’s number.
II. Fraction and Percent Composition
Sometimes people need to determine how much of a compound’s mass is made up of each element.
Water, H2O, for example has a molar mass of about 18 g.
Hydrogen’s mass is 2 g (1.0079 X 2 Hydrogen atoms). Oxygen’s mass is 16.00 g.
We can set up fractions for each element:
2.00
16.00
H=
= 0.112 = 11.2%. O =
= 0.888 = 88.8%.
18.00
18.00
This is called the percent composition. Determine the molar mass and percent composition of each
element below:
Molar Mass
Element 1 name
Element 2 name
Element 3 name
and percent
and percent
and percent
H2SO4
Ca(OH)2
HC2H3O2
CO2
N 2O
K3PO4
Al2SO4
C 6 H 12 O6
O’Ryan
98 grams
H - 1 + 1 =2
S=32
O- 16 X 4 = 64
98 g
H = 2/98
= .02 = 2%
S = 32/98
= .327 = 32.7%
O= 64/98
=.65 = 65%
Chemistry 2015
Molar Mass and Percent Composition
Name_____________________
Molar Masses:
Explain how you find the molar mass of an element or compound.
________________________________________________________________
One mole of anything has _____________________________ particles/pieces. This is called
________________________ number.
II. Fraction and Percent Composition
Sometimes people need to determine how much of a compound’s mass is made up of each element.
Water, H2O, for example has a molar mass of about 18 g.
Hydrogen’s mass is 2 g (1.0079 X 2 Hydrogen atoms). Oxygen’s mass is 16.00 g.
We can set up fractions for each element:
2.00
16.00
H=
= 0.112 = 11.2%. O =
= 0.888 = 88.8%.
18.00
18.00
This is called the percent composition. Determine the molar mass and percent composition of each
element below:
Molar Mass
Element 1 name
Element 2 name
Element 3 name
and percent
and percent
and percent
H2SO4
Ca(OH)2
HC2H3O2
CO2
N 2O
K3PO4
Al2SO4
C 6 H 12 O6
O’Ryan
Chemistry 2015
O’Ryan