Combustion Analysis
Determine the empirical formula and molecular formula of any C, H, O organic compound or hydrocarbon from combustion data (CO₂ and H₂O masses). Free online chemistry calculator with step-by-step breakdowns and charts.
About This Calculator
The Combustion Analysis Calculator determines the empirical formula and molecular formula of organic compounds from combustion data. Whether you are a chemistry student, researcher, or lab professional, this tool simplifies the quantitative analysis of carbon, hydrogen, and oxygen in unknown compounds.
In complete combustion, all carbon in the sample is converted to carbon dioxide (CO₂) and all hydrogen is converted to water (H₂O). The mass of carbon is calculated from the CO₂ mass using the ratio of atomic masses: mC = mCO₂ × 12.011 / 44.009. Similarly, the mass of hydrogen is found from H₂O: mH = mH₂O × 2 × 1.008 / 18.015. For C, H, O compounds, the oxygen mass is obtained by difference: mO = msample − mC − mH. Each mass is then converted to moles, and the simplest whole-number mole ratio gives the empirical formula.
If the molar mass is also provided, the calculator determines the molecular formula by computing the ratio n = molar mass / empirical formula mass and multiplying the empirical formula subscripts by n. This is essential for identifying unknown organic compounds in analytical chemistry.
Regional Notes
Combustion analysis is a universal laboratory technique taught in chemistry curricula worldwide. The calculation methodology is identical across all regions (India, US, UK, EU) since it is based on fundamental atomic masses and stoichiometric principles. The calculator uses standard IUPAC atomic masses (C=12.011, H=1.008, O=15.999 g/mol) accepted internationally.
Frequently Asked Questions
What is combustion analysis in chemistry?
Combustion analysis is a quantitative laboratory technique used to determine the empirical formula of an unknown organic compound. A weighed sample is burned completely in excess oxygen, and the masses of the combustion products (CO₂ and H₂O) are measured. From these masses, the amounts of carbon, hydrogen, and oxygen in the original sample are calculated, leading to the empirical formula.
How do you find the empirical formula from combustion analysis?
To find the empirical formula: (1) Calculate the mass of carbon from the CO₂ mass using the ratio of atomic masses (mass C = CO₂ mass × 12.011 / 44.009). (2) Calculate the mass of hydrogen from the H₂O mass (mass H = H₂O mass × 2 × 1.008 / 18.015). (3) For C, H, O compounds, find the oxygen mass by subtracting C and H masses from the sample mass. (4) Convert each mass to moles by dividing by the atomic mass. (5) Divide each mole value by the smallest mole value to get the simplest whole-number ratio.
What is the difference between empirical formula and molecular formula?
The empirical formula shows the simplest whole-number ratio of atoms in a compound (e.g., CH₂O), while the molecular formula shows the actual number of atoms in one molecule (e.g., C₃H₆O₃). To find the molecular formula, divide the compound's molar mass by the empirical formula mass, then multiply the empirical formula subscripts by this ratio.
Is the combustion analysis calculator free to use?
Yes, this combustion analysis calculator is completely free to use with no registration or subscription required. Simply enter your sample mass, CO₂ mass, and H₂O mass to get instant results.
Do I need to provide the molar mass to use this calculator?
No, the molar mass is optional. Without it, the calculator will determine the empirical formula and the empirical formula mass. If you also provide the molecular (molar) mass, the calculator will additionally determine the molecular formula.
What is the difference between a C, H, O compound and a hydrocarbon?
A hydrocarbon contains only carbon and hydrogen atoms. A C, H, O compound contains carbon, hydrogen, and oxygen atoms. When analyzing a hydrocarbon, the oxygen mass is not calculated since there is no oxygen in the sample. For C, H, O compounds, the oxygen mass is found by subtracting the carbon and hydrogen masses from the total sample mass.
How accurate are the results from combustion analysis?
Combustion analysis is highly accurate when performed correctly. Modern combustion analyzers can measure elemental composition to within ±0.1-0.3%. The accuracy depends on the purity of the sample, completeness of combustion, and precision of the mass measurements. Our calculator uses standard atomic masses (C=12.011, H=1.008, O=15.999) and the accepted stoichiometric ratios.
Can I share my combustion analysis results?
Yes, all input values are saved in the URL as query parameters. You can copy the URL from your browser's address bar to share your exact calculation with classmates, teachers, or colleagues. When they open the link, the calculator will auto-fill the values and compute the results automatically.