1. Empirical & Molecular Formulas

2. #1 find the empirical formula
40% carbon; 6.7% hydrogen; 53.3% oxygen
Remember:
Assume 100 g
Use molar mass to find moles of each element
Divide by smallest number of moles
Multiply if necessary to get to two whole numbers
CH2O

3. #3 empirical – don’t erase yet!
30.4% nitrogen; 69.6% oxygen
NO2

4. #3, continued (molecular)
If the compound in question 3 has a molar mass of 92 g/mol, what is the molecular formula?
Remember:
Find the mass of the empirical formula
Divide the mass of the molecular formula (given) by the mass of the empirical formula to get the multiplier
Multiply each subscript by the multiplier to get the molecular formula
N2O4

5. #7
A compound with the following composition has a molar mass of g/mol: 39.97% carbon; 13.41% hydrogen; 46.62% nitrogen. Find the molecular formula.
C2H8N2

6. #8 polarity
In a bond between phosphorous and chlorine, where do the electrons spend the most time?
Near chlorine

7. #9 polarity Determine if the following bonds are polar or nonpolar:
C – H
C – O
S – F
S – Cl
N – O nonpolar (3.1 – 3.5)
C – H nonpolar (2.6 – 2.2)
C – O polar (2.6 – 3.5)
S – F polar (2.6 – 4.0)
S – Cl polar (2.6 – 3.2)

8. #2 empirical
92.3% carbon; 7.7% hydrogen CH

9. #4
7.19% phosphorous; 92.81% bromine
PBr5

10. #5
70.0% iron; 30.0% oxygen
Fe2O3

11. #6
Naphthalene is a carbon and hydrogen containing compound often used in moth balls. The empirical formula is C5H4 and its molar mass is g/mol. Find the molecular formula.
C10H8