Combustion analysis

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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 has been determined the empirical formula or a partial empirical formula of the original compound can be calculated.

1 History
2 Combustion train
3 Calculation of empirical formula
- 3.1 Example
4 References

[edit] History

The method was invented by Joseph Louis Gay-Lussac. Justus von Liebig studied the method while working with Gay-Lussac between 1822 and 1824 and improved the method in the following years to a level that it could used as standard procedure for organic analysis.^[1]

[edit] Combustion train

A combustion train is an analytical tool for the determination of elemental composition of a chemical compound. With knowledge of elemental composition a chemical formula can be derived. The combustion train allows the determination of carbon and hydrogen in a succession of steps:

combustion of the sample at high temperatures with copper oxide as the oxidizing agent
collection of the resulting gas in an anhydrous agent (magnesium perchlorate or calcium chloride) traps generated water
collection of the remainder gas in a strong base (for instance potassium hydroxide) traps the generated carbon dioxide.

Analytical determination of the amounts of water and carbon dioxide from a known amount of sample gives the empirical formula.

[edit] Calculation of empirical formula

For every hydrogen atom in the compound 1/2 equivalent of water is produced. For every carbon atom in the compound 1 equivalent of carbon dioxide is produced

[edit] Example

Given 0.025 moles of water and 0.012 moles of carbon dioxide we can determine that there are four hydrogens for each carbon in the original compound. The compound is likely methane.