Determines empirical and molecular formulas from combustion analysis data of organic compounds containing carbon, hydrogen, and oxygen.
Empirical Formula
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Molecular Formula
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Empirical Formula Weight
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Carbon %
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Hydrogen %
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Oxygen %
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Combustion analysis is a quantitative analytical technique used to determine the empirical formula of organic compounds containing carbon, hydrogen, and oxygen. The compound is burned completely, and the masses of CO₂ and H₂O produced are measured.
First, calculate moles of carbon from CO₂ mass and moles of hydrogen from H₂O mass. For CHO compounds, find oxygen by difference. Then determine the simplest whole number ratio of C:H:O to get the empirical formula.
The empirical formula shows the simplest whole number ratio of atoms. The molecular formula shows the actual number of atoms in a molecule and is a whole number multiple of the empirical formula.
Divide the known molecular weight by the empirical formula weight to get a whole number multiplier. Multiply all subscripts in the empirical formula by this number to get the molecular formula.
Complete combustion occurs (all carbon becomes CO₂, all hydrogen becomes H₂O), no side reactions happen, and for CHO compounds, any oxygen present comes from the original compound, not from combustion air.
In CHO compounds, oxygen atoms in the original compound don't appear in the combustion products (CO₂ and H₂O). The oxygen percentage is calculated as 100% minus the carbon and hydrogen percentages.