1. Unit V: The Mole Concept
V.5. Empirical and Molecular Formulae

2. Empirical Formula Empirical Formula Simplest Formula
Gives the simplest whole number ratio of elements in a compound

3. Molecular Formula Molecular Formula
Gives the ACTUAL number of each kind of atom in a molecule and compound

4. Molecular vs. Empirical

5. Molecular vs. Empirical
Molecular Formula
Empirical Formula
P4O10
C10H22
C6H18O3
C5H12O
N2O4

6. Molecular vs. Empirical
Molecular Formula
Empirical Formula
P4O10
P2O5
C10H22
C5H11
C6H18O3
C2H6O
C5H12O
N2O4
NO2

7. Finding Empirical Formulas
A sample of an unknown compound is analyzed and found to contain 8.4 g of “C” 2.1 g of “H” and 5.6 g of “O”. Find the empirical formula.

8. Finding Empirical Formulas
Element
Mass (g)
Atomic
Mass
Moles
Sm.Moles
Smallest
Ratio C H O

9. Finding Empirical Formulas
0.888 grams of a compound made up of carbon, hydrogen and oxygen are found to contain g of carbon and g of hydrogen.
Find the mass of oxygen
Find the empirical formula

10. Finding Empirical Formulas
Element
Mass (g)
Atomic
Mass
Moles
Sm.Moles
Smallest
Ratio C H O

11. Finding Empirical Formulas
A while powder used in paints has the following composition:
Ba 69.58%
C %
O 24.32%
Find the Empirical Formula

12. Finding Empirical Formulas
Element
Mass(g)
Atomic
Mass
Moles
Sm.Moles
Smallest
Ratio Ba C O

13. Multiply ALL numbers by…. to get the Smallest Ratio
WHAT HAPPENS WHEN……..
is not near a whole #
__ Moles__
smallest moles
If ends in
a decimal of
Multiply ALL numbers by…. to get the Smallest Ratio
≈ 0.5 2
≈0.33 or ≈0.66 3
≈0.25 or ≈0.75 4
≈0.2, ≈0.4, ≈0.6, ≈0.8 5

14. Empirical to Molecular Formula
A compound has a molar mass of 60.0g/mol and its empirical formula is CH2O. Find the molecular formula.
Empirical
Molecular
Formula
Mass

15. Hebden
Do Exercises 46 (d, g, & m) on pages 93 & Exercises 48 and 52 on page 95 of Hebden
Read through Tutorial 5-1: Percent Mass and Empirical Formulas (Working in Pairs)
Do the Self-Test on Tutorial 5-1