1. Empirical Formulas Definition Ex:
A formula that gives the simplest whole number ratio of the different atoms in a compound.
H2O2 = hydrogen peroxide
HO = empirical formula for hydrogen peroxide
C6H12O6 = Glucose
Empirical Formula? =
Definition
Ex:

2. Empirical Formula Calculation
Empirical formulas are determined from % composition.
The % composition by mass of a compound is 56.6% K, 8.7% C, and 34.7% O. Find it’s empirical formula
Example:

3. Empirical Formulas Steps Assume 100g of the compound. (Change % to g)
K = ______g
C = ______g
O = ______g
Convert g to moles.
(HINT: Use dimensional analysis)

4. Empirical Formulas K = 1.45mol Show your DA! C = .72mol O = 2.17mol
3. Divide all moles by the smallest mole value.
K = 1.45mol/.72mol = 2.0
C = .72mol/.72mol = 1.0
O = 2.17mol/.72mol = 3.0
Show your DA!

5. Solve the following:
A compound is 80% C and 20% H. What is the empirical formula? (Follow the steps).
A compound was analyzed and found to contain 13.5g Ca, 10.8g O and .675g H. What is the empirical formula for the compound?

6. Solve the following:
A compound is 20.8% Magnesium, 42.7% Arsenic, and 36.5% O. What is the empirical formula?
Write the name of the compound!

7. Molecular Formulas Definition Example:
Show the types and numbers of atoms in a compound. (H2O2)
Same as the empirical formula or a whole # multiple of it.
C6H12O6 = molecular formula of glucose.
CH2O= empirical formula of glucose (or any sugar)
H2O = empirical and molecular formula of water
Definition
Example:

8. Molecular Formulas Need (or need to be able to calculate): Needed:
Empirical Formula (you may need to find this )
Formula Mass or Molar Mass of Molecular Compound (must be given)
Needed:

9. Molecular Formulas
The empirical formula of a compound is P2O5 and it has a formula mass of g. What is the molecular formula of the compound?
Solve

10. Molecular Formulas- Steps
Molar mass of the molecular compound.
g (from problem)
Empirical formula of the compound.
P2O5 (from problem)
Molar mass of the empirical formula.
2(Mass of P) + 5(Mass of O) = g
Molar mass of molecular formula (must be the one given)/ molar mass of empirical formula (always the same or smaller #)
g / g =2.0000
Multiply subscripts in empirical formula by answer above
2(P2O5 ) = P4O10

11. Remember!
By definition, the molecular formula is the same as or a whole number multiple of the empirical formula…
If your number did not come out perfect- CHECK YOUR MATH!

12. Solve the following:
A compound has 7.6g Nitrogen, 17.4g Oxygen, and a molar mass of 138g. What is the empirical formula?
What is the molecular formula?
Write the name of the compound!