1. Percent Composition - The percent composition of a component in a compound is the percent of the total mass of the compound that is due to that component.

2. 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.

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

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

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

6. 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

7. 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

8. 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

9. WWWWe Do Calculate the percentage mass contribution of phosphorus in phosphoric acid H 3 PO 4

10. 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 mass from % composition

11. 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 mass from % composition

12. 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 mass from % composition

13. 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 mass from % composition

14. 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 mass from % composition

15. Glucose contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass What is the empirical formula What is the molecular formula WWWWe Do