Chemistry / Chem 0501 · Procedure · 60–90 seconds
Combustion Analysis
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Combustion analysis burns a weighed sample of a carbon- and hydrogen-containing compound completely, then weighs the carbon dioxide and water produced to determine the sample's percent composition.
Burning a 0.00126-g polyethylene sample yields 0.00394 g CO2 and 0.00161 g H2O. Every carbon atom in the sample ends up in CO2, and every hydrogen atom ends up in H2O, so the masses of carbon and hydrogen in the original sample can be recovered from these two product masses using their known mole ratios, then compared back to the 0.00126-g starting mass to find the sample's percent composition.
The oxygen content of an oxygen-containing sample cannot be read directly from the CO2 and H2O masses — it must be found by subtracting the recovered carbon and hydrogen mass from the total sample mass.
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