1. molecular formula:
a whole-number multiple of an empirical formula…
…showing the total number of each atom in a molecule
formaldehyde CH2O
acetic acid C2H4O2
glucose C6H12O6
all same empirical formula:
(same ratio of atoms) CH2O

2. 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
multiple of emp. form.

3. 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
multiple of emp. form.

4. Quick Quiz.
1. True or False:
A molecular formula can be the same as an empirical formula.
Example:
Formaldehyde has the
empirical formula CH2O,
which is the formula of the actual molecule.

5. 2. Determine the molecular formula of a
Quick Quiz.
2. Determine the molecular formula of a
compound with % C, % H,
and 53.3 % O by mass that has a
molecular mass of 60 g/mol.
C2H4O2
CH2O
C2H3O
C2H4O
CH2O
x 1 mol C
12.01 g C
x 1 mol H
1.01 g H
x 1 mol O
16.00 g O
40.0 g C
6.70 g H
53.3 g O
3.33 mol C
6.63 mol H
3.33 mol O
= 1 C
= 2 H
= 1 O =
________
3.33
_________
= 2
2 (CH2O) =