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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. Steps. Assume a 100g sample . Change each mass into moles
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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
Steps • Assume a 100g sample. • Change each mass into moles • Divide each mole through by the smallest to obtain a ratio • Write the formula
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?
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?
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
The molecular weight of methyl benzoate is 136.0 amu. Is the empirical formula we determined the molecular formula? • What is the molecular formula?
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
Magnessium is burned in excess oxygen gas to form magnessium oxide. If 1.75g of Mg is initially burned and the mass of the oxide formed is found to be 2.90g, what is the formula of the magnessium oxide?