Combustion Analysis Calculator
Use this combustion analysis calculator to convert carbon dioxide and water combustion data into an empirical formula, and optionally scale it to a molecular formula.
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What This Combustion Analysis Calculator Helps You Do
This page helps you move from experimental combustion data to a chemical formula without doing the entire stoichiometry chain by hand. It covers both the standard hydrocarbon workflow and the CHO mass-balance workflow used in introductory and analytical chemistry.
The result panel shows the empirical formula first and then checks whether a supplied molar mass supports a molecular formula. That makes it easier to audit lab work instead of accepting a black-box answer.
How to Calculate Combustion Analysis Calculator
- Enter the combustion products: Supply the measured masses of carbon dioxide and water from the experiment.
- Choose the compound family: Use hydrocarbon mode when the unknown contains only C and H, or CHO mode when oxygen is also present.
- Reduce the mole ratios: Convert each element to moles and divide by the smallest value to obtain empirical subscripts.
- Scale to a molecular formula when possible: If you know the molar mass, compare it with the empirical-formula mass and multiply the subscripts by the nearest whole-number factor.
Combustion Analysis Calculator Formula
| Variable | Meaning | Unit |
|---|---|---|
| m(CO2) | Mass of carbon dioxide produced | g |
| m(H2O) | Mass of water produced | g |
| m(sample) | Original sample mass for CHO compounds | g |
| n(C), n(H), n(O) | Moles of each element in the unknown | mol |
| M | Molar mass used to scale empirical to molecular formula | g/mol |
Use the worked examples below to check how the formula behaves with real values. If the result looks unexpected, verify the unit assumptions and the meaning of each variable before interpreting the answer.
Worked Examples
- CO2: 1.760 g
- H2O: 0.720 g
- Molar mass: 42.08 g/mol
Result: Empirical formula CH2; molecular formula C3H6.
The combustion data show a 1:2 carbon-to-hydrogen ratio, and the molar mass scales the empirical unit by 3.
- Sample mass: 1.800 g
- CO2: 2.640 g
- H2O: 1.080 g
- Molar mass: 180.16 g/mol
Result: Empirical formula CH2O; molecular formula C6H12O6.
Oxygen is recovered by mass balance after carbon and hydrogen are assigned from the combustion products.
- CO2: 2.201 g
- H2O: 0.450 g
Result: Empirical formula CH.
A 1:1 elemental ratio points to a highly unsaturated hydrocarbon family.
- Sample mass: 0.900 g
- CO2: 1.320 g
- H2O: 0.540 g
Result: Empirical formula CH2O.
Without a molar mass, the empirical formula is still enough to describe the simplest whole-number composition.
How to Interpret Your Results
| Range | Meaning | Action |
|---|---|---|
| Clean whole-number ratios | The measured data are internally consistent. | Use the empirical formula directly or scale it with molar mass. |
| Ratios near fractions | Experimental rounding or moisture handling may be affecting the result. | Check whether doubling or tripling the ratio set produces stable whole numbers. |
| Negative oxygen mass in CHO mode | The sample mass is too small for the reported combustion products. | Recheck the measurements and the assumption that the compound contains only C, H, and O. |
Frequently Asked Questions
References
Last reviewed: March 2026