1. E MPIRICAL AND M OLECULAR F ORMULA

2. E MPIRICAL F ORMULAS An empirical formula indicates the simplest whole-number ratio for a molecule

3. C ALCULATING EMPIRICAL FORMULAS Step 1: Convert grams to moles Step 2: Divide all numbers by the smallest value Step 3: Use whole number ratio as subscripts **You just need the mass of each element**

4. E MPIRICAL FORMULA EXAMPLE What is the empirical formula for 2.50 g of a compound containing 0.900g of Calcium and 1.60 g of Chlorine?

5. Determine the empirical formula of a compound containing 2.644 g of gold and 0.476 g of chlorine.

6. D ETERMINING EMPIRICAL F ORMULA F ROM % C OMPOSITION Step 1: Assume 100 g, change % to grams Step 2: Convert moles to grams Step 3: Divide all numbers by the smallest Step 4: Use the # of moles as subscripts

7. E MPIRICAL FORMULA EXAMPLE Find the empirical formula of a substance composed of 40.00% C, 6.67% H and 53.33% O.

8. W HAT IS THE EMPIRICAL FORMULA OF A COMPOUND THAT IS 25.9% NITROGEN AND 74.1% OXYGEN ?

9. M OLECULAR F ORMULAS A molecular formula tells exactly how many atoms of each element are in a molecule. It is a whole number multiple of the empirical formula.

10. E MPIRICAL /M OLECULAR F ORMULA Using ratios- think whole numbers Empirical FormulaMolecular Formula An empirical formula indicates the simplest whole-number ratio for a molecule **Not common** CH 2 A molecular formula tells exactly how many atoms of each element are in a molecule. Is a multiple of the empirical formula C 2 H 4 C 5 H 10

11. D ETERMINING M OLECULAR F ORMULA F ROM E MPIRICAL F ORMULA Step 1: Divide the molar mass of the compound (given in the problem) by the molar mass of the empirical formula Step 2: Multiply each subscript by the answer to Step 2 **You need the actual molar mass of the compound**

12. M OLECULAR F ORMULA E XAMPLE Find the molecular formula of a compound with empirical formula of CH 2 O and molar mass of 180.18g.

13. F INDING THE MOLECULAR FORMULA FROM THE PERCENT COMPOSITION Step 1: Find empirical formula Step 2: Divide the molar mass of the compound (given in the problem) by the molar mass of the empirical formula Step 3: Multiply each subscript by the answer to Step 2

14. M OLECULAR F ORMULA E XAMPLE What is the formula of a gas whose molar mass is 30.0 grams and whose composition is 20.0 % H and 80.0% C?

15. A compound has an empirical formula of CH and a molar mass of 78 g/mol. What is its molecular formula.

16. A brown gas has the empirical formula of NO 2. Its experimental molar mass is 46 g/mol. What is its molecular formula?