Combustion analysis Combustion analysis is a method used in both organic chemistry and analytical chemistry to determine the elemental composition (more precisely empirical formula) of a pure organic compound by combusting the sample under conditions where the resulting combustion products can be quantitatively analyzed. Once the number of moles of each combustion product (in this case, carbon dioxide and water) has been determined the empirical formula of the original compound can be calculated. Note – in this activity you will determine the moles of carbon and the moles of hydrogen in the original sample from the moles of carbon dioxide and water produced respectively. The moles of the other component of the unknown sample must be determined through subtraction.

Use grams of CO2 to get grams of C 1 mol CO2 44.021 g CO2 1.86 g CO2 × 1 mol C 12.011 g C × × 1 mol CO2 1 mol C 0.507 g carbon Use grams of H2O to get grams of H 1 mol H2O 2 mol H 1.008 g H 0.76 g H2O × × × 18.015 g H2O 1 mol H2O 1 mol H 0.085 g hydrogen

Calculate grams of O through subtraction 1.27 g sample - 0.507 g carbon - 0.085 g hydrogen 0.678 g oxygen Convert to grams of C, H, and O to moles of C, H, and O Divide through by smallest moles to get empirical formula Determine molecular formula from molar mass and empirical mass