What if my compound contains no oxygen?

Leave the oxygen field at 0 or the tool will calculate it automatically. If C% + H% equals ~100%, the compound contains only carbon and hydrogen.

Why does the tool need the sample mass?

The sample mass lets the calculator find the oxygen content by subtracting the mass of C and H. Without it, oxygen cannot be determined from CO2 and H2O alone.

What is the difference between empirical and molecular formula?

The empirical formula shows the simplest whole-number ratio of atoms. The molecular formula is a whole-number multiple of it (e.g., empirical CH2O → molecular C6H12O6 for glucose).

Why are my ratios not whole numbers?

Experimental mass measurements always carry error. The tool rounds ratios to the nearest 0.1 and then to the nearest integer. If results look off, check whether your collected masses are reasonable.

Can I use milligrams instead of grams?

Yes — as long as all three mass values use the same unit, the mole ratios are identical.

Empirical Formula from Combustion Analysis

Name: Empirical Formula from Combustion Analysis
Availability: InStock
Author: Nham Vu

Enter sample mass plus masses of CO2 and H2O produced to get the empirical formula and elemental percentages.

Combustion Data

All masses in the same unit (g or mg).

Sample mass

Mass of CO₂ produced

Mass of H₂O produced

Compound contains nitrogen

Enter combustion data on the left to see the empirical formula.

Empirical Formula

Simplest whole-number atomic ratio

Mole Breakdown

Element	Mass (g)	Moles	Ratio	%

Elemental Composition

Step-by-Step

Summary

Enter sample mass plus masses of CO2 and H2O produced to get the empirical formula and elemental percentages.

How it works

Enter the mass of your organic sample in grams.
Enter the mass of CO2 collected from combustion.
Enter the mass of H2O collected from combustion.
The calculator finds moles of C (from CO2) and H (from H2O).
Oxygen mass is determined by subtraction from the sample mass.
Mole ratios are reduced to the smallest whole-number empirical formula.

Use cases

Determine the empirical formula of an unknown organic compound in a lab.
Check combustion analysis data in organic chemistry coursework.
Verify elemental composition percentages against experimental results.
Identify the simplest C/H/O ratio before calculating the molecular formula.
Support analytical chemistry assignments and exam preparation.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu