1. UNIT 5A Chapter 10: Chemical Quantities Molar Mass
Mrs. Mansberger

2. What is Molar Mass?
Element: The atomic mass of an element expressed in grams is the mass of one mole of the element.
Example: g Oxygen = 1 mol Oxygen
12.0 g Carbon = 1 mol Carbon
With your partner, find the molar masses of the following elements…
Chlorine
Sodium
Iron
35.5 g/mole
23.0 g/mole
55.8 g/mole

3. Compound: The sum of the atomic masses of each atom in the compound.
Example: SO3
Find the molar masses of each element.
Then multiply by the number of atoms of each element.
Finally, add the masses together.
S = 32.1 g
O = 16.0 g
X 1
= 32.1 g
X 3
= 48.0 g
80.1
g/mole
OR g SO3 = 1 mol SO3

4. Find the Molar Mass of a Compound
Find the molar mass of aluminum sulfate: Al2(SO4)3
Al = 27.0 g
S = 32.1 g
O = 16.0 g
X 2
= g
X 3
= g
X 12
= g +
342
g/mole
g/mole
OR 342 g Al2(SO4)3 = 1 mol Al2(SO4)3

5. Try these with your partner…
Find the molar mass of PCl3
P = g
Cl = 35.5 g
138 g PCl3 =
1 mol PCl3
X 1
= g
X 3
= g +
138
g/mole
Find the molar mass of H2CO3
H = 1.0 g
C = 12.0 g
O = 16.0 g
X 2
= g
62.0 g H2CO3 =
1 mol H2CO3
X 1
= 12.0 g
X 3
= 48.0 g +
62.0
g/mole