Empirical & Molecular Formulas

Empirical Formula: gives the smallest whole number ratio of atoms in a compound (completely simplified)

For IONIC COMPOUNDSempirical formula = chemical formula

Reviewing RatiosIn a classroom with 15 total kids, there are 3 kids with blue eyes, 8 kids with brown eyes, and 4 kids with green eyes. Find the following:

1)The ratio of blue eyed kids to kids in the class

2)The ratio of brown eyed kids to green eyed kids

3:15 or 1:5

8:4 or 2:1

Molecular Formula: gives the actual number of atoms for each element in a compound

Sometimes, the empirical formula is also the molecular formula (H2O)

Empirical Formula• HO• CH2O

• CH3O

Molecular Formula

• H2O2

• C2H4O2

• C3H9O3

To find EMPIRICAL FORMULA:1.Find moles of each element2.Divide by smallest mole3.Multiply to make whole (if still decimal- look at it

as if it was a fraction. For example, .33 is 1/3 so can multiply by 3)

2.128g Cl35.5g Cl1mol Cl

0.0599mol Cl1.203g Ca

40.1g Ca1mol Ca

0.03mol Cl

Ca0.03Cl0.0599

1. Find Mole

2. Divide by smallest mole

Ca0.03Cl0.05990.030.03

Ca1Cl2

3. Multiply to make whole (don’t need to here, since both are whole numbers

Since percent compositions are given, assume you have 100.0g of sample. The grams of each element will be the same as the percent Try on your own!

Answer: C3H4O3

1. Find Empirical formula CH2O

2. Find EFM C: 12.0gH: 1.0g X 2 = 2.0O: 16.0g

30.0g

3. Divide molecular mass by EFM

30.0g180.0g

= 6This means the true molecular formula is 6 times larger than the empirical

4. Multiply empirical formula by the answer from step 3

CH2Ox6 x6 x6C6H12O6