Empirical & Molecular Formulas

Empirical Formula: gives the smallest whole number ratio of atoms in a compound (completely simplified) For IONIC COMPOUNDS empirical formula = chemical formula

Reviewing Ratios In 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 3:15or 1:5 8:4or 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 (H 2 O) Empirical Formula HO CH 2 O CH 3 O Molecular Formula H 2 O 2 C 2 H 4 O 2 C 3 H 9 O 3

To find EMPIRICAL FORMULA: 1.Find moles of each element 2.Divide by smallest mole 3.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 Cl 35.5g Cl 1mol Cl mol Cl 1.203g Ca 40.1g Ca 1mol Ca 0.03mol Cl Ca 0.03 Cl Find Mole 2. Divide by smallest mole Ca 0.03 Cl Ca 1 Cl 2 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: C3H4O3C3H4O3

1. Find Empirical formulaCH 2 O 2. Find EFM C: 12.0g H: 1.0g X 2 = 2.0 O: 16.0g 30.0g 3. Divide molecular mass by EFM 30.0g 180.0g =6 This means the true molecular formula is 6 times larger than the empirical 4. Multiply empirical formula by the answer from step 3 CH 2 O x6 C 6 H 12 O 6