1. Percent Composition
% Oxides
% hydrides

2. Chemical Formulas Can Give Percentage Composition
CO and CO2 are both C and O, but have diff. % compositions.

3. Percent Composition by mass
percentage composition-
% by mass of each element in a compound.
verifies substance’s identity
used to compare ratio of mass contributed by element in 2 different subsstances
mass element
molar mass compound x 100%

4. Percentage Composition of Iron Oxides

5. Calculate % comp. of copper(I) sulfide a copper ore called chalcocite.
Step 1 find Molar mass
Step 2 divide coppers contribution by molar mass , then X by %100
Step 3 divide sulfurs contribution by molar mass, then X by %100

6. Molar Mass and Percent Composition
Find molar mass of Cu2S.
2(Cu)(63.55g/mol) =
1(S)(32.07g/mol) =
159.17g/mol Cu2S
Divide mass of ea. element by molar mass of compound
79.85%Cu
20.15% S

7. % Hydrate hydrate: 1,2,3,4,5,6,7,8,9,10 compound containing water
Prefixes represent # of water molecules attached to parent
mono,di,tri,tetra,penta,hexa,hepta,octa,nona,deca
1,2,3,4,5,6,7,8,9,10
Calculate % comp Ce(SO4)2• 4H2O
Molar mass: ______________
% Ce :____________________
% S : ____________________
% 0 : ____________________
% H2O :___________________

8. % Hydrate hydrate: 1,2,3,4,5,6,7,8,9,10 compound containing water
Prefixes represent # of water molecules attached to parent
mono,di,tri,tetra,penta,hexa,hepta,octa,nona,deca
1,2,3,4,5,6,7,8,9,10
Calculate % comp Ce(SO4)2• 4H2O
Molar mass: _ g/mol Ce(SO4)2•4H2O
% Ce :____________________34.65%Ce
% S : ____________________15.86%S
% 0 : ____________________ 31.67%O
% H2O :___________________ 17.83%H2O

9. % Hydrate hydrate: 1,2,3,4,5,6,7,8,9,10 compound containing water
Prefixes represent # of water molecules attached to parent
mono,di,tri,tetra,penta,hexa,hepta,octa,nona,deca
1,2,3,4,5,6,7,8,9,10
Calculate % comp Ce(SO4)2• 4H2O
Molar mass: g/mol Ce(SO4)2•4H2O
_______________________________________=34.65%Ce
_______________________________________=15.86%S
_______________________________________=31.67%O
______________________________________=17.83%H2O