# Combustion Analysis Calculator

Determine the empirical formula of an organic compound from combustion analysis data. Enter CO₂ and H₂O masses to find C, H, O composition.

## What this calculates

Determine the empirical formula of an organic compound from combustion analysis data. Enter the sample mass and the masses of CO₂ and H₂O produced to calculate the elemental composition and empirical formula.

## Inputs

- **Sample Mass** (g) — min 0.001 — Mass of the organic compound sample combusted.
- **CO₂ Produced** (g) — min 0 — Mass of carbon dioxide produced during combustion.
- **H₂O Produced** (g) — min 0 — Mass of water produced during combustion.
- **Contains Nitrogen?** — Toggle on if the compound contains nitrogen.
- **N₂ Produced** (g) — min 0 — Mass of nitrogen gas produced. Only used if compound contains nitrogen.

## Outputs

- **Mass of Carbon** (g) — Mass of carbon in the sample.
- **Mass of Hydrogen** (g) — Mass of hydrogen in the sample.
- **Mass of Oxygen** (g) — Mass of oxygen in the sample (by difference).
- **Empirical Formula** — formatted as text — The simplest whole-number ratio of atoms.
- **Molecular Formula Hint** — formatted as text — Approximate empirical formula weight for determining molecular formula.

## Details

Combustion analysis is a classical technique for determining the elemental composition of organic compounds. A known mass of the compound is burned completely in excess oxygen, and the masses of CO₂ and H₂O produced are measured.

How It Works

- All carbon in the compound is converted to CO₂. Moles of C = moles of CO₂ = mass(CO₂) / 44.01.

- All hydrogen is converted to H₂O. Moles of H = 2 × moles of H₂O = 2 × mass(H₂O) / 18.015.

- If nitrogen is present, it is collected as N₂. Moles of N = 2 × moles of N₂.

- Oxygen is determined by difference: mass(O) = sample mass − mass(C) − mass(H) − mass(N).

- The mole ratios are reduced to the simplest whole numbers to give the empirical formula.

From Empirical to Molecular Formula

The empirical formula gives the simplest ratio of atoms. To find the molecular formula, you need the actual molecular weight (from mass spectrometry or other methods). Molecular formula = n × empirical formula, where n = molecular weight / empirical formula weight.

## Frequently Asked Questions

**Q: What compounds can be analyzed by combustion analysis?**

A: Combustion analysis works for compounds containing carbon and hydrogen, and optionally oxygen, nitrogen, and sulfur. The compound must burn completely in excess oxygen. It is the standard method for organic compounds (CHO, CHON, CHOS).

**Q: How is oxygen content determined?**

A: Oxygen is determined by difference: mass of O = sample mass - mass of C - mass of H - mass of N. This means oxygen content depends on the accuracy of all other measurements. If the compound contains other elements (like S or halogens), those must be accounted for separately.

**Q: Why might the ratios not come out to whole numbers?**

A: Experimental error can cause slight deviations. The calculator tries multipliers from 1 to 6 to find the best whole-number ratios. Sometimes the true ratio involves fractions like 1.5 or 2.5, requiring multiplication by 2 to get whole numbers (e.g., CH₂.5 becomes C₂H₅).

**Q: How do I get the molecular formula from the empirical formula?**

A: Divide the known molecular weight by the empirical formula weight to get n. The molecular formula is the empirical formula multiplied by n. For example, if the empirical formula is CH₂O (weight 30.03) and the molecular weight is 180.16, then n = 6, giving C₆H₁₂O₆ (glucose).

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Source: https://vastcalc.com/calculators/chemistry/combustion-analysis
Category: Chemistry
Last updated: 2026-04-21