Molar Mass and Percent Composition
Name____________________________
Date ___________
Determine the formula mass for each of the following compounds. Individual atomic masses can be found on your
periodic chart. You must show all work here or on another sheet of paper.
1 sulfur atom in the sulfate ion,
Find Quantity of
atoms
Atomic mass from periodic table
and the 3 outside is distributive
across ( ), so there are 3 atoms of
sulfur in the compound.
Example: Find formula mass of Al2(SO4)3
2
Al
x 26.98 =
54.0 g
3
S
x 32.1 =
96.3 g
12
O
x 15.999 =
192.0 g
Property is distributive, so 3 x 4 = 12!
M.M. = 342.3 g
amu
Names, molar mass, and percent of component indicated:
1. K2S
(%K)
2. Pb(ClO4)2
(% ClO4)
3. KH2PO4
(%O)
4. Ca3(PO4)2
(%Ca)
5. NiCl2
(%Ni)
6. Fe(NO3)3
(%NO3)
7. CoCl2●6H2O
(%H2O)
8. CuCl2●2H2O
(%H2O)
9. K2SO4●10H2O
(%H2O)
10. Cd(NO3)2●4H2O
(%H2O)
Mass contribution for
Each element
Add the mass contribution of
each element.