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Compounds: Mass percent composition
Solutions:
- Determine the mass percent of each element in Al 2 (SO 4 ) 3.
The mass percent of each element in a compound can be determined and the sum of the
percentages for all elements should be equal to 100%.
2 4 3
Al % Al 100 Al (SO )
n mass of mass mass of
g
g
×
= ×
×
= ×
2 4 3
S
Al (SO )
n mass of mass S mass of
g
g
×
= ×
×
= ×
2 4 3
O
% O 100
Al (SO )
n mass of mass mass of
g
g
×
= ×
×
= ×
- What mass of CaCl 2 will contain 15.0 g of chlorine?
One way to find the mass is to use the mass percent of chlorine in the compound. There
are other ways to solve this problem.
2
Cl % Cl 100 CaCl
n mass of mass mass of
g
g
×
= ×
×
= ×
Now, use the mass percentage to determine the relationship between the mass of the
chlorine and the mass of the compound. Remember that a percentage is out of 100 so we
know that in a 100 g sample of CaCl 2 , there will be 63.89 g Cl.
2 2
100 CaCl 15.0 Cl 23.5 CaCl 63.89 Cl
g g g g
When using the percentage as a relationship, check that the correct units and substance are
on the bottom so the units cancel out correctly.
- Which substance has a greater percent by mass of hydrogen: C 4 H 8 or C 8 H 18?
The percent of hydrogen can be calculated for each compound and C 8 H 18 is found to have a
higher percentage of hydrogen by mass.
4 8 4 8
H
% H in C H 100 C H
n mass of mass mass of
g
g
×
= ×
×
= ×
8 18 8 18
H
% H in C H 100 C H
n mass of mass mass of
g
g
×
= ×
×
= ×
