1. Empirical Formulas
formaldehyde CH2O
(toxic preservative)
acetic acid C2H4O2
(vinegar)
glucose C6H12O6
(simple sugar)
all have the same basic or “empirical” formula
CH2O

2. empirical formula:
the smallest whole-number ratio of the atoms in a compound.
Examples:
CH3 HO PbO2 C2H6N
Non-Examples:
C2H6 H2O2 Pb2O4 C6H18N3

3. Acetylene (C2H2) is a gas used in welder’s torches.
These two compounds of carbon both have the same empirical formula (CH) but different molecular formulas.
Styrene (C8H8) is used in making polystyrene.

4. Percent to Mass Mass to Mole Divide by Small Times ‘till Whole
What is the empirical formula of a compound that is analyzed and found to contain % N and % O?
Percent to Mass
Mass to Mole
Divide by Small
Times ‘till Whole

5. What is the empirical formula of a compound that is analyzed and found to contain % N and % O?
Percent to Mass
Mass to Mole
Divide by Small
Times ‘till Whole
25.9 g N
74.1 g O
x 1 mol N
14.01 g N
x 1 mol O
16.00 g O
= 1.85 mol N
= 4.63 mol O
________
1.85
= 1 N
= 2.5 O
x 2 = 2 N
x 2 = 5 O
N2O5

6. 1,6-diaminohexane is used to make nylon
1,6-diaminohexane is used to make nylon. What is the empirical formula if it is % C, % H, and % N?
62.1 g C
13.8 g H
24.1 g N
x 1 mol C
12.01 g C
x 1 mol H
1.01 g H
x 1 mol N
14.01 g N
= 5.17 mol C
= mol H
= 1.72 mol N
________
1.72
_________
= 3 C
= 8 H
= 1 N
C3H8N

7. molecular formula:
a whole-number multiple of the empirical formula of a compound
formaldehyde CH2O
acetic acid C2H4O2
glucose C6H12O6
all have the same empirical formula
CH2O

8. Calculate the molecular formula of a compound with the empirical formula CH4N and a molar mass of 60.0 g/mol.
molecular mass = multiple of emp. form.
empirical mass
empirical mass
1(C) + 4(H) + 1(N) =
(1.01) = g/mol =
30.06
≈ 2
2 (CH4N) =
C2H8N2

9. Calculate the molecular formula of benzene with the empirical formula CH and a molar mass of 78 g/mol.
molecular mass = multiple of emp. form.
empirical mass
empirical mass
1(C) + 1(H) =
= g/mol
78 =
13.02
≈ 6
6 (CH) =
C6H6

10. Quick Quiz!
1. An empirical formula shows the __________ of atoms in a compound.
lowest common number
highest whole ratio
lowest whole number ratio
average ratio

11. Quick Quiz.
2. Which of the following is NOT an empirical formula?
CH3
H2N CH
C3H6

12. Quick Quiz.
3. True or False:
A molecular formula can be the same as an empirical formula.
True False
Example:
Formaldehyde has the
empirical formula CH2O,
which is its molecular formula as well.

13. Quick Quiz.
4. Determine the molecular formula of a compound that contains % C, 6.71 % H, and % O by mass and has a molar mass of g/mol.
C2H4O2
CH2O
C2H3O
C2H4O