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 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?

Step 1 Assume a 100g sample g C 16.2 g O 71.7 g Cl

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

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

Step 4 Write the formula COCl 2

Example 2 A g sample of methyl benzoate, a compound used in perfumes, is found to contain g of carbon,.316 g of hydrogen, and g of oxygen. What is the empirical formula? C4H4OC4H4O

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 amu. Is the empirical formula we determined the molecular formula? What is the molecular formula?

Combustion Example The combustion of g of ascorbic acid produces 1.50 g of CO 2 and.405 g of H 2 O. Determine the empirical formula. Find grams of each substance Find moles of each Divide to find ratio