1. Percent Composition: Is the percentage of the total mass due to each element within a compound

4. To calculate the percent composition of a component in a compound: 1.Find the molar mass of the compound by adding up the masses of each atom in the compound.

5. 2. Calculate the mass due to the component in the compound for which you are solving by adding up the mass of these atoms.

6. 3. Divide the mass due to the component by the total molar mass of the compound and multiply by 100.

7. Calculate the percent composition of carbon in each of the following: CO 2

8. Calculate the percentage mass contribution of Oxygen in glucose C 6 H 12 O 6 Step One find the molecular mass of the molecule 6 carbons 6 x 12 72 12 hydrogens 12 x 1 12 6 Oxygens 6 x 16 96 Total 180 Step two circle the mass contribution of the element required (oxygen) 6 carbons 6 x 12 72 12 hydrogens 12 x 1 12 6 Oxygens 6 x 16 96 Total 180 Step three find the percentage contribution % = Mass contribution of element x 100 Total molecular mass of molecule % = 96 x 100 180 53.33 % of the mass of a glucose molecule is caused by oxygen

9. Step two circle the mass contribution of the element required (oxygen) 6 carbons 6 x 12 72 12 hydrogens 12 x 1 12 6 Oxygens 6 x 16 96 Total 180

10. Step three find the % contribution % = Mass contribution of element x 100 Total molecular mass of molecule % = 96 x 100 180 53.33 % of the mass of a glucose molecule is caused by oxygen

11. Calculate the percentage mass contribution of phosphorus in phosphoric acid H 3 PO 4

12. A compound is found to contain 65.5% carbon, 5.5% hydrogen, and 29.0% oxygen Find the empirical formula of the compound For these question you simply work backwards Calculating molecular formula from % composition

13. For these question you simply work backwards Step 1 Divide the % by RAM to find ratio 65.5/12 5.46 5.5/1 5.5 29.0/16 1.81 Calculating molecular formula from % composition

14. This give us the ratio C =5.46 H = 5.5 O= 1.81 Step 2 divide by the lowest number C =3.01 H =3.03 O =1 The empirical formula is C 3 H 3 O 1 Calculating molecular formula from % composition

15. If the molar mass of the compound is 110 grams/mole, what’s the molecular formula? Step 3 Find the molecular mass of the empirical formula The molecular mass of C 3 H 3 O would be 55g/mol to find the molecular formula Calculating molecular formula from % composition

16. Step 4 use the formula Formula x (Molar mass/ empirical mass) C 3 H 3 O x 110/55 C 3 H 3 O x 2 C 6 H 6 O 2 Calculating molecular formula from % composition

17. Glucose has a molecular mass of 180 and contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass What is the empirical formula? What is the molecular formula?

18. Write & Respond

19. A compound composed of: 63.55% iron (Fe) and 36.45% oxygen (O) by mass and a molecular mass of 173.6. What is the empirical formula and the molecular formula Step 1 To find molar ratio divide given percentages of masses by the individual atomic masses 63.55/55.6 iron (Fe) = 1.143 36.45/16 oxygen (O) = 2.276

20. A compound composed of: 63.55% iron (Fe) and 36.45% oxygen (O) by mass and a molecular mass of 173.6. What is the empirical formula and the molecular formula Step 2 Divide ratios by the lowest value Fe 1.143/1.143 =1 O 2.276/1.143 = 1.99 FeO 2

21. A compound composed of: 63.55% iron (Fe) and 36.45% oxygen (O) by mass and a molecular mass of 173.6. What is the empirical formula and the molecular formula Step 4 use the formula ratio Formula x (Molar mass/ empirical mass) FeO2 x 173.6/87.8 = FeO2 X 2 Fe 2 O 4