1. Calculating Percent Composition From Formula % Composition: % by mass of each element in compound % Composition: % by mass of each element in compound molar mass element x 100% molar mass element x 100% total molar mass compound

2. Calc. % Composition Continued 1) Find total molar mass of element 2) Divide by molar mass of compound 3) Multiply by 100 Hint: The percentage of all elements should add up to = 100%.

3. Calculating % Composition Find % composition for each element in CaCO 3 Ca: 40.08g Ca__ x 100% = 40.04% Ca: 40.08g Ca__ x 100% = 40.04% 100.09g CaCO 3 100.09g CaCO 3 C: 12.01g C x 100 %= 12.00% C: 12.01g C x 100 %= 12.00% 100.09g CaCO 3 100.09g CaCO 3 O: 48.00g O x 100%= 47.96% O: 48.00g O x 100%= 47.96% 100.09g CaCO 3 100.09g CaCO 3

4. Calculating % Composition From Data mass element in cmpd. x 100% mass element in cmpd. x 100% molar mass compound molar mass compound Ex: A 3.60g sample of a compound contains 1.70g of oxygen. What is the percent compostion of oxygen in the compound? _____1.70g O______ x 100 = 47.2 %O 3.60g compound 3.60g compound

5. What is the percent nitrogen in a 11.2g sample that contains 9.48g N?

6. Empirical Formula- lowest whole number ratio of elements in a compound Empirical Formula- lowest whole number ratio of elements in a compound Molecular formula- actual# of elements in a compound as it appears in nature Molecular formula- actual# of elements in a compound as it appears in nature Molecular and empirical formulas may or may not be the same Molecular and empirical formulas may or may not be the same

7. Examples Empirical/Molecular Formulas Empirical Empirical CO 2 CO 2 HO HO C 2 H 4 O C 2 H 4 O Molecular CO 2 H 2 O 2 C 4 H 8 O 2

8. To find empirical formula: 1. Change % comp. to g 1. Change % comp. to g 2. Change g to mol 2. Change g to mol 3. Divide by lowest number of moles 3. Divide by lowest number of moles 4. Round or Multiply to get whole numbers 4. Round or Multiply to get whole numbers 5. #’s become subscripts 5. #’s become subscripts Tips for #4:.2 or lower, round down.2 or lower, round down.8 or above round up.5 X by 2.3 X 3.25,.75 X 4

9. What is the empirical formula of a compound that is 25.9 % N & 74.1%O? What is the empirical formula of a compound that is 25.9 % N & 74.1%O? 25.9g N x 14.01g= 1.85 mol ÷ 1.85= 1 x 2=2 1 mol 1 mol 74.1g O x 16.00g= 4.63 mol ÷ 1.85= 2.5x 2=5 1 mol 1 mol N 2 O 5 N 2 O 5

10. To find Molecular Formula 1.Calculate mass of empirical formula 2. Divide molecular mass/empirical mass 3. Multiply subscripts in empirical formula by number calculated in step 2

11. Calculate molecular formula of compound whose molar mass is 216.03g/mol with an empirical formula of N 2 O 5. Calculate molecular formula of compound whose molar mass is 216.03g/mol with an empirical formula of N 2 O 5.

12. A compound is composed of 40.68% C, 5.08% H & 54.24%O. It has a molecular mass of 118.1g/mol. Find the empirical & molecular formula. A compound is composed of 40.68% C, 5.08% H & 54.24%O. It has a molecular mass of 118.1g/mol. Find the empirical & molecular formula.