Chemical Composition CW
These problems are to be done in your notebook!
1. Determine the percent composition of propane, C3H8.
2. Write the molecular formula of a compound with an empirical formula of C2OH4
and a molar mass of 88.105 grams per mole.
3. The percentage composition of acetic acid is found to be 39.9% C, 6.7% H, and
53.4% O. Determine the empirical formula of acetic acid.
4. The molar mass for question #3 was determined by experiment to be 60.0 g/mol.
What is the molecular formula?
5. Calculate the mass percent of carbon, nitrogen and oxygen in acetamide,
C2H5NO.
6. A compound with an empirical formula of C4H4O and a molar mass of 136 grams
per mole.
7. A 50.51 g sample of a compound made from phosphorus and chlorine is
decomposed. Analysis of the products showed that 11.39 g of phosphorus atoms
were produced. What is the empirical formula of the compound?
8. When 2.5000 g of an oxide of mercury, (HgxOy) is decomposed into the elements
by heating, 2.405 g of mercury are produced. Calculate the empirical formula.
9. The compound benzamide has the following percent composition. What is the
empirical formula?
C = 69.40 % H= 5.825 % O = 13.21 % N= 11.57 %
10. A component of protein called serine has an approximate molar mass of 100
g/mole. If the percent composition is as follows, what is the empirical and
molecular formula of serine?
C = 34.95 % H= 6.844 % O = 46.56 % N= 13.59 %
Chemical Composition CW
1. Determine the percent composition of propane, C3H8.
3C
3(12.011)
36.033
(100) = 81.714% C
(100) =
(100) =
C3 H 8
3(12.011) + 8(1.0079)
44.0962
8H
8(1.0079)
(100) =
(100) = 18.285% H
C3 H 8
3(12.011) + 8(1.0079)
2. A compound with an empirical formula of C2OH4 and a molar mass of 88.105
grams per mole.
Mass of empirical formula = EF = 2(12.011) + 15.999 + 4(1.0079) = 44.0526 g/mol
88.105
2(C2OH4) = C4O2H8
=2
44.0526
3. The percentage composition of acetic acid is found to be 39.9% C, 6.7% H, and
53.4% O. Determine the empirical formula of acetic acid.
39.9
6.7
53.4
= 3.32 mol C
= 6.6 mol H
= 3.34 mol O
12.011
1.0079
15.999
3.32
6.6
3.34
=1
=2
=1
3.32
3.32
3.32
CH2O
4. The molar mass for question #3 was determined by experiment to be 60.0 g/mol.
What is the molecular formula?
EF = 12.011 + 2(1.0079) + 15.999 = 30.0258 g/mol
60.0 / 30.0258 = 2
C2H4O2
5. Calculate the mass percent of carbon, nitrogen and oxygen in acetamide,
C2H5NO.
24.022
5.0395
(100) = 40.669 % C
(100) = 8.5318 % H
59.0675
59.0675
14.007
15.999
(100) = 23.714 % N
(100) = 27.086 % O
59.0675
59.0675
6. A compound with an empirical formula of C4H4O and a molar mass of 136 grams
per mole.
136
EF = 68.0746
=2
C8H8O2
68.0746
7. A 50.51 g sample of a compound made from phosphorus and chlorine is
decomposed. Analysis of the products showed that 11.39 g of phosphorus atoms
were produced. What is the empirical formula of the compound? PCl3
50.51 – 11.39 = 39.12 g Cl
11.39
39.12
= 0.3677 mol P
= 1.103 mol Cl
30.974
35.453
1.103

PCl3
= 2.9997
0.3677
8. When 2.5000 g of an oxide of mercury, (HgxOy) is decomposed into the elements
by heating, 2.405 g of mercury are produced. Calculate the empirical formula.
2.5000 – 2.405 = 0.095 g O
2.405
0.095
= 0.0119896 mol Hg
= 0.00593787 mol O
200.59
15.999
0.0119896

Hg2O
=2
0.00593787
9. The compound benzamide has the following percent composition. What is the
empirical formula?
C = 69.40 % H= 5.825 % O = 13.21 % N= 11.57 % C7H7NO
10. A component of protein called serine has an approximate molar mass of 100
g/mole. If the percent composition is as follows, what is the empirical and
molecular formula of serine?
C = 34.95 % H= 6.844 % O = 46.56 % N= 13.59 %
C3H7NO3 empirical formula
C3H7NO3 molecular formula