
shows the smallest whole-number ratio of
the atoms in the compound, NOT the
actual number of atoms in the compound

CH only means it is a 1:1 ratio between
carbon and hydrogen
 could be C2H2 (ecetylene), or C6H6
(benzene), or C8H8 (styrene)

a molecular formula is the same as, or a multiple
of, the empirical formula
 it is based on the actual number of atoms of each
type in the compound, NOT just the ratio
 the following all have same empirical formula
(CH2O at a 1-2-1 ratio) but different molecular
formulas



C2H4O2 is the molecular formula of ethanoic acid
CH2O is the molecular formula of methanol
C6H12O6 is the molecular formula of glucose
Compound
Water
Hydrogen Peroxide
Glucose
Methane
Ethane
Octane
Molecular Formula
Empirical Formula
H 2O
H2O2
C6H12O6
CH4
C2H 6
H2O
HO
CH2O
CH4
CH3
C4 H 9
C8H18

A compound is found to contain 16g of C and 4g
of H. What is the empirical formula?
1mol C
= 1.33 mole C
12.01 g C
 4gHx
1mol H = 4 mole H
1.01 g H
 a formula is not just the ratio of atoms, it is also the
ratio of moles
 this leaves a ratio of C1.33H4 which is not a possible
formula

16 g C x
1.33 is too far off from 1
 divide both by the lowest number (1.33)
to see the ratio

1.33/1.33 = 1
 4/1.33 = 3
 empirical formula is CH3


Calculate the empirical formula of a compound
composed of 38.67g C, 16.22g H, and 45.11g N.



38.67 g C x
1mol C
= 3.220 mole C
12.01 g C
16.22 g H x
1mol H = 16.09 mole H
1.01 g H
45.11 g N x 1mol N
= 3.219 mole N
14.01 g N



3.220 mole C
16.09 mole H
3.219 mole N
• C3.22H16.09N3.219
If we divide all of these by the smallest
number (3.219), it will give us whole numbers and
therefore the empirical formula

C1H5N1 is the empirical formula