1. Empirical and Molecular Formulas
“Sistine Madonna,” Rafael Sanzio, Italian.

2. What is a Molecular Formula?
The formula of a compound that uses subscripts to show how many atoms of each element is in a molecule of the compound. Ex: C6H12O6 Ex: CO2 Ex: N2H4

3. What is an Empirical Formula?
A molecular formula whose subscripts have been reduced to the smallest whole number ratio.
Ex: C6H12O6 becomes:
CH2O
Ex: CO2 becomes:
CO2
Ex: N2H4 becomes:
NH2

4. How do you determine the empirical formula of a compound?
Convert all grams or percents to moles.
Divide all of the moles by the smallest of the number of moles to determine the mole ratios.
Use the mole ratios (as whole numbers*) as subscripts in the empirical formula.
*Multiply all mole ratios by 2 if one of the mole ratios ends in .5 .

5. Example
A compound is composed of 4.00 g of calcium and g of bromine. What is its empirical formula?

6. Example
A compound contains 48.63% carbon, 8.18% hydrogen, and % oxygen. What is its empirical formula?

7. What do you need to determine the molecular formula of a compound?
The empirical formula of the compound.
The molar mass of the compound.

8. Example 1
The empirical formula for a compound is P2O5. Its molar mass is g/mol. What is its molecular formula?

9. 3 Easy, Painfree steps to solve
1. Determine the molar mass of the empirical formula.

10. 3 Easy, Painfree steps to solve
2. Divide molar mass of molecular formula by molar mass of empirical formula.

11. 3 Easy, Painfree steps to solve
3. Multiply subscript of empirical formula by factor determined in step 2.

12. Example 2
A compound is composed of g of carbon, 1.20 g of hydrogen, and 9.60 g of oxygen. The molar mass of the compound is 180. g/mol. Find the molecular formula of the compound.