Combustion Analysis

When a compound containing carbon and hydrogen is subject to combustion with oxygen in a special combustion apparatus all the carbon is converted to CO₂ and the hydrogen to H₂O (Figure 1). The amount of carbon produced can be determined by measuring the amount of CO₂ produced. This is trapped by the sodium hydroxide, and thus we can monitor the mass of CO₂ produced by determining the increase in mass of the CO₂ trap. Likewise, we can determine the amount of H produced by the amount of H₂O trapped by the magnesium perchlorate.

Figure 1 : Combustion analysis apparatus

One of the most common ways to determine the elemental composition of an unknown hydrocarbon is an analytical procedure called combustion analysis. A small, carefully weighed sample of an unknown compound that may contain carbon, hydrogen, nitrogen, and/or sulfur is burned in an oxygen atmosphere,Other elements, such as metals, can be determined by other methods. and the quantities of the resulting gaseous products (CO₂, H₂O, N₂, and SO₂, respectively) are determined by one of several possible methods. One procedure used in combustion analysis is outlined schematically in Figure 1 and a typical combustion analysis is illustrated in Examples 1 and 2.

Figure 1: Steps for Obtaining an Empirical Formula from Combustion Analysis. (CC BY-NC-SA; anonymous by request)