Combustion Analysis Calculator
Convert combustion products into elemental moles and arrive at empirical formulas for unknown organic compounds.
Leave blank to estimate oxygen by difference.
How to Use This Calculator
Run the combustion experiment
Burn a known mass of sample and capture the CO2 and H2O produced using absorption tubes.
Weigh the products
Measure the mass gain of CO2 and H2O traps, and record the original sample mass.
Enter the measurements
Provide the masses here, including any directly measured oxygen if available.
Interpret the empirical formula
The resulting whole number ratios give the empirical composition of the compound.
Formula
nC = m(CO2) / M(CO2)
nH = 2 × m(H2O) / M(H2O)
nO = [m(sample) - mC - mH] / M(O)
Convert the mole ratios to whole numbers to obtain the empirical formula. Include measured oxygen mass if available.
Example
For 5.86 g CO2, 2.68 g H2O, and 4.50 g sample: nC = 0.133 mol, nH = 0.298 mol, nO = 0.042 mol, giving C3H7O empirical composition.
Full Description
Combustion analysis oxidizes a compound completely, translating carbon to CO2 and hydrogen to H2O. Measuring these products provides the elemental composition.
The empirical formula is obtained by converting the elemental masses to moles, normalizing to the smallest amount, and reporting the ratios as whole numbers.
Frequently Asked Questions
What if oxygen is not present in the compound?
The calculator will return zero moles of oxygen if the difference mass is negligible, leading to a formula without oxygen.
Can I include nitrogen or halogens?
Standard combustion analysis requires trapping those species separately. This tool focuses on C, H, and O only.
How do I convert to molecular formula?
Compare the empirical formula mass to the molar mass from other experiments. Multiply the empirical formula as needed.
Why might oxygen mass be negative?
Analytical error can cause the difference to be slightly negative. Use the optional oxygen input or re-run the measurements.
Does combusting in excess oxygen matter?
Yes. Ensure excess oxygen is supplied so all carbon and hydrogen are fully oxidized and captured.