1. EMPIRICAL FORMULA
VS.
MOLECULAR FORMULA 

2. EMPIRICAL FORMULA VS. MOLECULAR FORMULA
Empirical Formula: the simplest whole number ratio of atoms in a compound.
Molecular Formula: shows how many atoms of each element are present in a molecule or compound.

3. Empirical vs. Molecular
Identify the following as molecular or
empirical.
CH6
C2H2
C12H6
Empirical Molecular Molecular
C2H4O
C8H8S4
Empirical
Molecular

4. Calculating Empirical Formulas
 Use the following poem to remember
the steps:
"Percent to mass,
Mass to moles, Divide by small, Multiply ‘til whole"

5. Calculating Empirical Formulas
 Example #1: Find the empirical formulas for a compound with 13.5% of calcium, 10.8% oxygen, 0.675% of hydrogen.
 Step 1: If the element is given in a percent,
assume 100 g.
13.5% Ca = 13.5 g Ca
10.8% O = 10.8 g O
0.675% H = g H

6. Example #1 Continue element to moles using the molar mass.
 Step 2: Convert the mass of each
element to moles using the molar mass.

7. Example #1 Continue smallest mole value.
 Step 3: Divide each mole value by the
smallest mole value.
 Smallest mole value = 0.337

8. Example #1 Continue
 Step 4: If CLOSE, Round to the nearest whole number.
 If answer is NOT close to a whole number, you will need to multiply by a factor of 2 or 3.
If answer ends with .5, multiply by 2.
If answer ends with .3 or .6, multiply by 3.
 You MUST multiply EACH element by the factor!
 Example #1 Continue
 Ca = 1
 O = = 2
 H = = 2

9. Example #1 Continue using answers as the subscripts.
Step 5: Write Empirical Formula
using answers as the subscripts.
CaO2H2 = Ca(OH)2

10. Calculating Empirical Formulas
 Example #2: Determine the empirical formula for a compound composed of 40.00% C, 6.72% H, and 53.29% O.

11. Calculating Empirical Formulas
Example #3
57.4% Carbon
6.16% Hydrogen
9.52% Nitrogen
27.18% Oxygen

12. Calculating Molecular Formulas
Step 1: Find the molar mass of the
empirical formula.
Step 2: Divide the molecular mass by the empirical mass (big number by small number)
Step 3: Multiply answer by each subscript in the empirical formula to get molecular formula.

13. Calculating Molecular Formulas
 Example #1: What is the molecular formula of a compound whose molar mass is 60.0 g/mol and empirical formula is CH4N?

14. Calculating Molecular Formulas
 Example #2: What is the molecular formula of
CH3O if its molar mass is 62 g/mol?

15. Calculating Molecular Formulas
Example #3: Find the molecular formula for a compound with an empirical formula of C2H8N and a molecular mass of 46 grams per mole.

16. Which of the following is an empirical formula?
A. C3H6
C. CH4
B. C2H8
D. C4H10