Percent Composition
Name:________________________ Hr: ___
So far we have discussed the composition of compounds in terms of the numbers of atoms. Often it is
useful to know a compound’s composition in terms of the masses of its elements. Consider the formula
for caffeine (C8H10N4O2). The percent composition for each of the elements in a molecule of
caffeine can be determined by using the following equation:
% composition
of a given
mass of the element in 1 mole of the compound
=
element
x 100 %
molar mass of the compound
% carbon = (8 x 12.0 g) x 100 = 49.5 %
194.0 g
% hydrogen = (10 x 1.0 g) x 100 = 5.1 %
194.0 g
% nitrogen = (4 x 14.0 g) x 100 = 28.9 %
194.0 g
% oxygen = (2 x 16.0 g) x 100 = 16.5 %
194.0 g
Calculate the percent composition for the first element in each of the following minerals:
Common Name
Formula
1. Stibnite
Sb2S3
2. Bismuthinite
Bi2S3
3. Proustite
Ag3AsS3
4. Enargite
Cu3AsS4
5. Bournonite
PbCuSbS3
6. Jamesonite
Pb4FeSb6S14
7. Zincite
ZnO
8. Corundum
Al2O3
9. Hematite
Fe2O3
10. Ilmenite
FeTiO3
Molar Mass
Percent of 1st Element
Common Name
Formula
11. Stibnite
Sb2S3
12. Bismuthinite
Bi2S3
13. Proustite
Ag3AsS3
14. Enargite
Cu3AsS4
15. Bournonite
PbCuSbS3
16. Jamesonite
Pb4FeSb6S14
17. Zincite
ZnO
18. Corundum
Al2O3
19. Hematite
Fe2O3
20. Ilmenite
FeTiO3
Molar Mass
Percent of 1st Element