Combustion Analysis Calculator
Free Combustion analysis Calculator for chemical reactions. Enter variables to compute results with formulas and detailed steps.
Reviewed by Manoj Kumar, Mathematics Educator
Formula
Moles C = mass CO2 / 44.01 | Moles H = 2 * mass H2O / 18.015
Combustion analysis burns an organic sample in excess O2. Each mole of CO2 contains one mole of C, and each mole of H2O contains two moles of H. Mass of O is found by difference. Mole ratios give the empirical formula.
Worked Examples
Example 1: Combustion of an Unknown Hydrocarbon
Problem:0.500 g of an organic compound produces 1.467 g CO2 and 0.600 g H2O. Find the empirical formula.
Solution:Moles CO2 = 1.467/44.01 = 0.03334 mol = moles C\nMoles H2O = 0.600/18.015 = 0.03331 mol, moles H = 0.06662\nMass C = 0.03334 * 12.011 = 0.4003 g\nMass H = 0.06662 * 1.008 = 0.0671 g\nMass O = 0.500 - 0.4003 - 0.0671 = 0.0326 g\nMoles O = 0.0326/15.999 = 0.00204\nRatio C:H:O = 16.3:32.6:1 = ~16:33:1
Result:Empirical formula determination from C, H, O ratios
Example 2: Simple Combustion - Ethanol
Problem:1.000 g sample produces 1.913 g CO2 and 1.174 g H2O.
Solution:Moles CO2 = 1.913/44.01 = 0.04347 mol C\nMoles H2O = 1.174/18.015 = 0.06517 mol, H = 0.1303 mol\nMass C = 0.5222 g, Mass H = 0.1314 g\nMass O = 1.000 - 0.5222 - 0.1314 = 0.3464 g\nC:H:O ratio = 2:6:1 => C2H6O
Result:Empirical formula: C2H6O (ethanol)
Frequently Asked Questions
What is combustion analysis in chemistry?
Combustion analysis is an analytical technique used to determine the empirical formula of an organic compound by burning it in excess oxygen and measuring the masses of combustion products. Carbon in the sample becomes CO2, hydrogen becomes H2O, and nitrogen becomes N2. By weighing these products, you can calculate the moles of each element in the original sample. Any remaining mass is attributed to oxygen. This technique was developed by Justus von Liebig in the 1830s and remains a standard method for elemental analysis of organic compounds.
How do you find oxygen content from combustion analysis?
Oxygen content is determined by difference. First, calculate the mass of carbon from CO2 and the mass of hydrogen from H2O. If nitrogen is present, calculate its mass from N2. Subtract all these masses from the total sample mass to find the mass of oxygen. This indirect method is necessary because oxygen from the sample mixes with the excess oxygen used for combustion, making it impossible to measure directly. If the sum of C, H, and N masses exceeds the sample mass, recheck your calculations as this indicates an error.
What are common sources of error in combustion analysis?
Common errors include incomplete combustion leaving unburned carbon (soot), moisture contamination of the sample or absorption tubes, air leaks in the apparatus allowing atmospheric gases to interfere, and incomplete absorption of CO2 or H2O by the traps. Halogen-containing compounds can produce HCl or other acids that interfere with water measurement. Sulfur compounds produce SO2 which must be trapped separately. Modern automated analyzers minimize these errors but require careful calibration with standard compounds of known composition.
References
Reviewed by Manoj Kumar, Mathematics Educator · Editorial policy