Combustion Analysis Calculator

Combustion analysis is a lab technique chemists use to determine the chemical formula of an unknown organic compound by burning it and measuring the combustion products. Enter your sample mass, CO₂ produced, and H₂O produced into the Combustion Analysis Calculator, then select your compound type (C, H, O or hydrocarbon) to get the empirical formula, along with carbon, hydrogen, and oxygen percentages. Add an optional molecular weight to also calculate the full molecular formula.

g

Mass of organic compound sample before combustion

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Mass of carbon dioxide produced

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Mass of water produced

g/mol

If known, used to determine molecular formula

Results

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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Frequently Asked Questions

What is combustion analysis?

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.

How do you find the empirical formula from combustion analysis?

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.

What's the difference between empirical and molecular formulas?

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.

How do you find the molecular formula from 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.

What assumptions are made in combustion analysis?

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.

Why might oxygen percentage be calculated by difference?

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.