1. These Formulas are a Royal Pain Actually, it’s “Empirical” Formulas not “Imperial” Formulas

2. Types of Formulas Empirical Formula – Simplest ratio of atoms in a molecule Molecular Formula – Actual ratio of atoms in a molecule Structural Formula – Actual bonding pattern for molecule Examples of each type of formula – Oxalic Acid Emp: HCO 2 Molecular: H 2 C 2 O 4 Structural: O O C-C H-O O-H

3. What is the value of an empirical formula? Can be used for identification Easy and cheap to find – Emp form  ~$100 – Mol. Form  ~$10,000 to $100,000 – Structural  ~$250,000 Little equipment needed

4. How do you find an empirical formula? Take mass information (grams or %) and convert to moles using MW from pd. Table Reduce the mols of each element by dividing by the smallest* Evaluate the values – If very near to whole numbers, round off – If _.5, double all values – If _.33, triple all values – If _.25, quadruple all values

5. An example NutraSweet is 57.14% C, 6.16% H, 9.52% N, and 27.18% O. Calculate the empirical formula of NutraSweet Yuck! My dad had to use this junk when I was a kid. It’s much better now.

6. Calculating the moles of each element Convert 57.14 g of C to molesmoles 57.14 g C = XX = 4.76 mol C 12 g 1 mol Convert 6.16 g of H to moles 6.16 g H = XX = 6.16 mol H 1 g 1 mol Convert 9.52 g of N to moles 9.52 g N = X X = 0.68 mol N 14 g 1 mol Convert 27.18 g of O to moles 27.18 g O = X X = 1.70 mol O 16 g 1 mol

7. Then, divide by the smallest (We hope that works…) The smallest number of moles is 0.68 so we’ll divide each by that value – C: 4.76/0.68 = 7 C – 6.16/0.68 = 9 H – 0.68/0.68 = 1 N – 1.70/0.68 = 2.5 O Do we have whole numbers?NO! Since the oxygen has a 2.5 ratio we double all values to get whole number ratios (2.5 doubled gives 5) This gives 14 C, 18 H, 2 N, and 5 O.

8. The answer- C 14 H 18 N 2 O 5

9. Your turn A compound has the following mass profile: – 43.4% Na – 11.3% C – 45.3% O Is this sodium carbonate or sodium oxalate? Please note that the world is inside a chemical flask.