1. 1 Chapter 7 Chemistry Empirical Formulas/molecular formulas LOOK AT: Pages 245-249

2. Empirical vs Molecular Formula C2H6C2H6 CH 3 Empirical formula - Smallest whole number ratio of atoms in a compound Molecular formula true or actual ratio of the atoms in a compound.

3. 3 Types of Formulas The formulas for compounds and molecules can be expressed as an empirical formula and as a molecular formula. Empirical Molecular CHC 2 H 2 CHC 6 H 6 CO 2 CH 2 OC 5 H 10 O 5

4. Calculating Empirical Formula 1. Given: mass or percent of each element. If percent, just change % to g. 2. Convert grams to moles. 3. Divide ALL mole ANSWERS by the smallest number moles. By doing this, you find the subscripts. You may have to round to a whole number….the number can only be off by a little. 4. If any of your subscripts turn out to be.25,.50, or.75, you will need to multiply by 2, 3, or 4 to get a whole number.

5. Practice Find the empirical formula of a compound that contains 75.0 % Carbon and 25.0% Hydrogen. Find the empirical formula for a sample of 25.9% N and 74.1% O. 5

6. practice A typical charcoal briquette that is used in making a BBQ fire is composed of 43.2 g of Carbon. When the Charcoal lump is burned, it combines with oxygen and the resulting compound has a mass of 159.0 g. What is the empirical formula of the compound? 6

7. Empirical formulas of hydrates EX: A 5.00 g sample of a hydrate Copper (II) Nitrate is heated and 3.90 g of the anhydrous salt remains. Calculate the empirical formula of the hydrate. Name the hydrate. 7

8. Finding molecular formula from the empirical formula 1.Find the molar mass of the empirical formula 2.Divide the molar mass of the empirical formula by the molar mass of the molecular formula(will be given in the problem)--- you should get a whole number. 3.Take this number and multiply it to each subscript in the Empirical Formula. 4.The new formula is the molecular formula. 8

9. Molecular Formula The empirical formula for ethylene is CH 2. Find the molecular formula if the molecular mass is 28.1 g/mol?

10. 10 Practice A compound has a molar mass of 176.0 and an empirical formula of C 3 H 4 O 3. What is the molecular formula?