1. Wake-up
Determine the empirical formula for the following: 28.4% Copper and 71.6% Bromine

2. What are Molecular Formulas? How to calculate molecular formulas?

3. Empirical Formula
A chemical formula that shows the lowest whole number ratio of all atoms in a compound

4. Molecular Formula
A chemical formula that shows the total number and kinds of atoms in a molecule

5. Compound A is Empirical Formula Compound B is Molecular Formula
Recall from yesterday
Compound A is Empirical Formula
Compound B is Molecular Formula

6. How to find Molecular Formulas?
1. Write down what you know.
The simplest formula for butane is C2H5 and its molecular mass is 60g/mol. What is the molecular formula of butane?
Empirical formula = C2H5
Molar Mass = 60g/mol

7. How to find Molecular Formulas?
Calculate/Find the Empirical Formula
(if needed)
The simplest formula for butane is C2H5 and its molecular mass is 60g/mol. What is the molecular formula of butane?
C2H5

8. How to find Molecular Formulas?
3. Calculate the empirical formula mass (efm) using the empirical formula
C = 2 x = 24.02
H = 5 x 1.00 = 5
Empirical Formula Mass =
29.02

9. How to find Molecular Formulas?
4. Divide the molar mass (that is provided in the problem) by the empirical formula mass
The simplest formula for butane is C2H5 and its molecular mass is 60g/mol. What is the molecular formula of butane?
60g/mol
29.02g =
2 mole

10. How to find Molecular Formulas?
5. Multiply the empirical formula subscripts by the whole number you found in step 4 to get the molecular formula.
C2H5
C4H10 2 x =

11. Example #1
The simplest formula for vitamin C is C3H4O3. Experimental data indicates that the molecular mass of vitamin C is about 180 g/mol. What is the molecular formula of vitamin C?

12. Example #2
A compound contains 18.8% sodium, 29% chlorine, and 52.2% oxygen, by mass. If the molar mass of the compound in g/mol, determine the empirical and molecular formulas.

13. Example #3
Caffeine has an elemental analysis of 49.48% carbon, 5.190% hydrogen, 16.47% oxygen, and 28.85% nitrogen. It has a molar mass of g/mol. What is the molecular formula of caffeine?

14. What are Molecular Formulas? How to calculate molecular formulas?