# Empirical vs. Molecular Formula - St. Mary CSS Chemistry11U 2010

```Empirical vs. Molecular Formula
Our experience with chemicals involves the use of
molecular formulae. This formula communicates the
number of atoms of each kind of element present in 1
molecule of compound. The empirical formula can be
thought of as a reduced version of the molecular formula.
The empirical (simplest) formula indicates the lowest
whole number ratio of the elements in a compound.
*
Copy table 6.1 on page 207 in your notes using the
Problems:
a)
P2O4
b) C4H10
c)
N2 O4
d) N2O5
Write the empirical formula for each of the
following:
Example 1: Determine the empirical formula of a
compound composed of 70.1% silver, 9.1%
nitrogen, and 20.8% oxygen.
Solution:
Element
Let there be 100.0 g of the compound.
Mass
(g)
Molar
Mass
(g/mol)
Amount
(mol)
Ratio
silver
70.1
107.9
0.65
1
nitrogen
9.1
14.0
0.65
1
oxygen
20.8
16.0
1.30
2
Therefore the empirical formula is AgNO2.
Example 2: A sample of matter consists of 29.1% Na,
40.5% S, and 30.4% O. Determine the
empirical formula of this compound.
Solution: Let there be 100.0 g of the compound.
Element
Mass
(g)
Molar
Mass
(g/mol)
Amount
(mol)
sodium
29.1
23.0
1.27
1
2
sulphur
40.5
32.1
1.26
1
2
oxygen
30.4
16.0
1.90
1.5
3
Therefore the empirical formula is Na2S2O3.
Homework
1.