EMPIRICAL VS.
MOLECULAR
Empirical formula
• Is the simplest form of a formula
• Is written in the lowest possible
ratio
• E.g., CH2O or CH
• Will be reduced. May or may not
exist in this form in the real world.
Molecular formula
• Is the true formula or actual ratio
of the atoms in a compound.
• E.g., C2H4O2 or C6H6
• Will not be reduced. Formula
describes a substance as it
actually exists.
Empirical or Molecular?
• Na2O
empirical & molecular
___________________
• C3H6
molecular
___________________
• K2SO4
empirical & molecular
___________________
• C6H12O6
molecular
___________________
Keep in mind that for some compounds, its
empirical formula can also be its molecular formula.
Which pair has the same empirical
formula?
• Na2O and Na2O2
• C6H12O6 and CH2O
• C3H6 and C5H12
• C6H6 and C5H5
Calculating an Empirical Formula
1. Determine the mass of each element.
2. Convert the mass of each to moles. 
3. Find the mole to mole ratios of each element
by dividing the number of moles of each element
by the smallest number of moles.
4. If the ratio is not a whole number, multiply each
ratio by a factor to make them all whole
numbers.
5. Write the formula using the mole ratio as the
subscript for the formula.
Find the empirical formula of 69.5% O &
30.5% N.
• Step 1: Divide % or grams by its atomic mass
to get moles of each element.
69.5 g O 1 mol O
15.999 g O
30.5 g N 1 mol N
14.007 g N
= 4.344 mole O
= 2.177 mole N
Find the empirical formula of 69.5% O &
30.5% N.
• Step 2: Divide smallest mole number in each
element to get ratio of that element.
4.344 mole O
2.177 mole
=2O
2.177 mole N
=1N
2.177 mole
Find the empirical formula of 69.5% O &
30.5% N.
• *This answer becomes the subscript for
that element; round to nearest whole
number if .8 or higher or lower than .2.
Answer = NO2
Independent Practice:
1. Analysis of a compound shows that it contains 10.88g of
calcium and 19.07g of chlorine. Determine the empirical
formula of this compound.
Independent Practice:
2. One of the most commonly used white pigments in paint
is a compound of titanium and oxygen that contains 5.99 g
titanium by mass and 4.01 g oxygen by mass. Determine
the empirical formula and name for this compound.
Independent Practice:
3. Used in the production of nylon, adipic acid is an
organic compound composed of 49.31% C, 43.79% O, and
the rest is hydrogen. Determine the empirical formula of
adipic acid.
Calculating Molecular Formulas
• The molecular formula will have
the same ratio as the empirical
formula.
• To determine a molecular formula,
we will multiply the empirical
formula by a whole number factor
(WNF).
Calculating Molecular Formulas
1. Empirical Formula = P2O5
Molar Mass= 283.88 g/mol
What is the molecular formula of this compound?
empirical mass = 141.943 g/mol
WNF =
283.88 g/mol
141.943 g/mol
(P2O5)2  P4O10
=2
2. Nitrogen and oxygen form multiple
molecular compounds together. One of these
compounds is used to fuel space shuttles and
has the empirical formula NO2. If the molar
mass of this compound is 92.02 g/ mol, what is
the molecular formula?
• 3.Butane is commonly used in lighters. It is
composed of 17.37% hydrogen and 82.63%
carbon . It has a molar mass of 58.17 g/mol. What
is the molecular formula of butane?
**Fix typo in your packet, please.
4. Vitamin C is 40.91% C, 4.587% H, and
the remaining is oxygen. If the molar mass
of Vitamin C is about 180 g/mol, determine
the empirical and molecular formula.
Complete pages 20-21 for Homework!!!!