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% Composition, Empirical Formulas, & Molecular Formulas

% Composition, Empirical Formulas, & Molecular Formulas. Chapter 9 sections 3 & 4. % Composition. % = (part / whole ) x 100 When calculating the % composition, you are calculating the % of each element in a compound. % Composition. Calculate the % Composition of MgO. Mg = 24.31g O = 16.00g

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% Composition, Empirical Formulas, & Molecular Formulas

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  1. % Composition, Empirical Formulas, & Molecular Formulas Chapter 9 sections 3 & 4

  2. % Composition • % = (part / whole ) x 100 • When calculating the % composition, you are calculating the % of each element in a compound

  3. % Composition • Calculate the % Composition of MgO Mg = 24.31g O = 16.00g Total = 40.31g / 40.31 / 40.31 X 100 X 100 = 60.31 % Mg = 39.69% O

  4. % Composition • Calculate the % Composition of iron (III) oxide • % Fe = 69.94% • % O = 30.06%

  5. Empirical & Molecular Formulas • Empirical formula – the smallest whole number ratio of elements • Molecular formula – the true number of elements in a compound

  6. Empirical Formula • What is the empirical formula for H2O2? • HO • What is the empirical formula for C6H12O6? • CH2O

  7. Steps for Calculating the Empirical Formula • List your givens • Change % to grams • Change grams to moles • Divide everything by the smallest number of moles • Write your formula

  8. Empirical Formula Problem • Calculate the empirical formula of a compound containing 40.05 % S and 59.95 % O. 1 mol S = 32.07 g S 1 mol O = 16.00 g O 1.249 mol 3.747 mol / / 1.249 mol = 1 1.249 mol = 3 40.05 g S x 59.95 g O x SO3

  9. Empirical Formula Problem • Calculate the empirical formula for a compound containing 48.64 g C, 8.16 g H, and 43.20 g O. • C3H6O2

  10. Steps for Calculating Molecular Formula • Calculate the empirical formula • Get the molecular mass of the empirical formula that you just determined • Divide the experimentally determined molecular mass (given) by the molecular mass of the empirical formula • You will get a whole number • Multiply everything in the empirical formula by this number

  11. Molecular Formula Problem • Calculate the molecular formula of a compound containing 40.68%C, 5.08%H, and 54.25%O with an experimentally determined molecular weight of 118.1 g/mol

  12. Molecular Formula Problem 40.68g C x 1 mol C = 3.387 / 3.387 = (1)2 = 2 12.01 g C 5.08g H x 1 mol H = 5.04 / 3.387 = (1.5)2= 3 1.01 g H 54.25 g Ox 1 mol O = 3.390 / 3.387 = (1)2 = 2 16.00 g O C2H3O2

  13. Molecular Formula Problem • C2H3O2 • Molecular Mass = 59.04 • EDMM / EFMM = 118.1 / 59.04 = 2 • Molecular Formula • C4H6O4

  14. Molecular Formula Problem • Calculate the molecular formula of a compound containing 57.84 g C, 3.64 g H, and 38.52 g O with an experimentally determined molecular mass of 249.21 g/mol • C12H9O6

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