Empirical Formula – Notes

The
smallest

Circle the formulas below which are empirical formulas (remember – you are looking for
compounds with the simplest whole number ratio of atoms).
C2H6
CaCl2

is the simplest possible formula. It gives the
ratio of atoms in a substance.
KMnO4
H2O2
H2F2
P4H10
C6H6
Al2O3
Na2S2O3
C6H12O6
H3PO4
C4H10
There are 3 steps to follow if you want to find an empirical formula:
1.
2.
3.
 Example 1:
Calculate the empirical formula for a compound having 37.70% sodium, 22.95% silicon, and 39.35%
oxygen by mass.
 Example 2:
What is the empirical formula for a compound having 43.67% Phosphorous and 56.33% oxygen?
Empirical Formula – Practice
What is the empirical formula of the compounds below?
1. 52.7% potassium, 47.3% chlorine
2. 22.1% aluminum, 25.4% phosphorous, 52.5% oxygen
3. 13% magnesium, 87% bromine
Molecular Formula – Notes

______________________ __________________________ are formulas which describe the TRUE
molecule of a substance.

Molecular formulas tell you the ____________________________ of each element in a compound.

There are 3 steps to follow:
1. Calculate the _______________________________ (look in your notes)
2. ____________________________________________________
3. _______________________________________ by your ____________ to get the true molecular
formula.

Example 1
The empirical formula of a compound is NO2. Its molecular mass is 92g/mol. What is the molecular
formula?

Example 2
A compound is found to contain 75% carbon and 25% hydrogen. The molecular mass is 32g. What is
the molecular formula?
Molecular Formula – Practice
1. The empirical formula of a compound is CH2. Its molecular mass is 70 g/mol. What is the
molecular formula?
2. A compound is found to be 40.0% carbon, 6.7% hydrogen and 53.5% oxygen. Its molecular mass
is 60 g/mol. What is its molecular formula?
3. The molar mass of a compound is 92 g/mol. Analysis of a sample of the compound indicates that
is contains 0.606 g N and 1.390 g O. Find its molecular formula.