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Empirical Formulas

Empirical Formulas. Empirical formula tells the relative number of atoms of each element in a compound Mole concept provides a way of calculating the empirical formula Also called the simplest formula. Example.

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Empirical Formulas

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  1. Empirical Formulas

  2. Empirical formula tells the relative number of atoms of each element in a compound • Mole concept provides a way of calculating the empirical formula • Also called the simplest formula

  3. Example • Phosgene, a poison gas used during World War I, contains 12.1 percent C, 16.2 percent O, and 71.7 percent Cl. What is the empirical formula of phosgene?

  4. Step 1 • Assume a 100g sample. • 12.1 g C • 16.2 g O • 71.7 g Cl

  5. Step 2 • Change each mass into moles • 1.01 mol C • 1.01 mol O • 2.02 mol Cl

  6. Step 3 • Divide each mole through by the smallest to obtain a ratio • 1 C: 1O: 2Cl

  7. Step 4 • Write the formula • COCl2

  8. Example 2 • A 5.325 g sample of methyl benzoate, a compound used in perfumes, is found to contain 3.758 g of carbon, .316 g of hydrogen, and 1.251 g of oxygen. What is the empirical formula? • C4H4O

  9. Molecular Formula • The empirical formula may or may not be the true molecular formula • To obtain the molecular formula, we must know the molecular weight

  10. The molecular weight of methyl benzoate is 136.0 amu. Is the empirical formula we determined the molecular formula? • What is the molecular formula?

  11. Combustion Example • The combustion of 1.000 g of ascorbic acid produces 1.50 g of CO2 and .405 g of H2O. Determine the empirical formula. • Find grams of each substance • Find moles of each • Divide to find ratio

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