Combustion analysis is a method used in chemistry to determine the atomic composition of a substance by burning it under controlled conditions. It helps to determine the empirical formula of the sample, which shows the type and relative numbers of atoms. However, it does not provide information about the molecular or structural formula. It is mainly used for carbon-based organic compounds, and a gas analyzer instrument is used to complete the analysis.
In chemistry, combustion analysis is a method used to determine the atomic composition of a substance. Using this method, a chemist can take an accurately measured mass of an unknown substance and burn it under controlled conditions, in order to analyze the combustion products and then determine the empirical formula of the sample. The empirical formula of a substance refers to the type of atoms that make up the substance and the relative numbers of each type of atom, expressed as the simplest possible ratio in whole numbers. For this reason, the empirical formula is sometimes referred to in organic chemistry as the simplest formula.
Although combustion analysis methods may allow a scientist to determine the empirical formula of an unknown substance, they provide no information about either the molecular formula or the structural formula of the substance. These two formulas provide additional information that cannot be ascertained by combustion analysis. The molecular formula is very similar to the empirical formula, with the exception that, in addition to showing the type and relative ratio of each type of atom, it also shows the absolute number of atoms in each molecule of the substance. The structural formula provides even more information, showing exactly how the atoms in the molecule are connected to each other.
Combustion analysis is mainly used to determine the empirical formulas of unknown carbon-based organic compounds. When the sample of the parent compound is burned, in the presence of oxygen, the carbon atoms of the sample are converted to carbon dioxide and the hydrogen atoms are converted to water. Carbon dioxide is known as carbon “oxide” because it consists of one carbon atom joined to two oxygen atoms. Water is a hydrogen oxide, as it consists of two hydrogen atoms joined to one oxygen atom. Likewise, other elements present in the original sample will be converted, during the combustion process, into oxides of the original elements.
A gas analyzer instrument used for combustion analysis typically consists of a heated combustion chamber, supplied with a flow of oxygen, and a series of traps. The flow of oxygen passes through the combustion chamber and, as the sample under analysis is burned, this flow of oxygen carries the combustion products with it. These products are in the form of gases, which are retained in the outlet traps, where they can be measured to complete the analysis.
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