Combustion Analysis
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Combustion analysis is a powerful technique for determining the simplest (or empirical) formula of a compound. A simplest formula is the lowest whole number ratio of elements that can represent the composition of a compound. The molecular formula of a compound is the whole number ratio of atoms that are actually present in a molecule. Sometimes the simplest formula is the same as the molecular formula; sometimes it is not. Consider the following two cases.

Sucrose has a molecular formula C₁₂H₂₂O₁₁. This is also its simplest formula.
Glucose has a molecular formula C₆H₁₂O₆. However, its simplest formula is CH₂O because this is the lowest whole number ratio that can represent the ratio of atoms found in this molecule.

In combustion analysis, a known mass of a compound (with an unknown formula but known elemental makeup) is burned in an excess of oxygen gas. The carbon and hydrogen present in the compounds are converted into carbon dioxide (CO₂) and water (H₂O) respectively. The masses of these products are determined experimentally (Would you like to learn more about the combustion analysis apparatus?). This information can be used to find out how much carbon and hydrogen were present in the original compound burned. Once this is known, the simplest formula of the compound can be determined. More details will be provided later.

Before you start, you will need the worksheet for this investigation.
If you don't have a copy, download and print it now. Once you have the worksheet you can
start the experiment.