Overview
The composition mode walks through mass → moles → ratios → integerisation → empirical formula. Molecular mode checks whether a target molar mass matches the empirical unit within tolerance. Combustion mode converts CO₂ and H₂O masses into CHO ratios, while Hydrate mode estimates xH₂O from mass loss.
Download the whole trail as CSV or grab a shareable URL via Ctrl+S / Ctrl+L. Integerisation tolerance, maximum multiplier k, GCD reduction, Hill ordering, and custom atomic weights help align the tool with lab data or course conventions.
Static example before you compute: a 40.0% C, 6.7% H, 53.3% O composition is treated as a 100 g sample, converted to mole ratios, and read as the empirical formula CH2O. The result table below should show the same stages after the calculator runs.
Calculator
Integerisation & atomic weight settings
Results
How it's calculated
FAQ
Can I combine percent and gram data in Composition mode?
Absolutely. Percent inputs are converted using the standard 100 g assumption, while gram inputs stay untouched. Each conversion step is logged so the class can follow the algebra.
What if oxygen from combustion becomes negative?
The app flags a warning and keeps the intermediate ratios so you can revisit the measurements or include other hetero atoms such as N, S, or Cl.
Do share links capture my settings?
Yes. Shared URLs embed tolerance, max k, the GCD toggle, element ordering, and any custom atomic weights, ensuring reproducible results.
Which composition data should I enter first?
Start with the measured element percentages or masses. If you have combustion data, enter CO2 and H2O values carefully before adding molar mass for a molecular-formula check.
Why can another formula calculator give a different final formula?
Differences usually come from atomic weights, rounding tolerance, oxygen-by-difference handling, or the allowed multiplier from empirical to molecular formula. Compare the mole ratios before comparing only the final formula.
Empirical and molecular formula notes
Choose the input basis
Percent composition assumes a 100 g sample. Mass composition uses the grams you enter directly. Combustion mode derives carbon and hydrogen from CO2 and H2O, then treats oxygen by difference when appropriate.
Convert to mole ratios
The key step is dividing each element amount by atomic weight, then scaling ratios to small whole numbers. Review the step log when a ratio is close to a half, third, or quarter.
Molecular formula check
When molar mass is supplied, the empirical formula mass is multiplied to match the molecular formula. If the multiplier is not near an integer, revisit measurements and tolerances.
Common mistakes
Do not mix percent and gram rows unless you intend that basis. Do not assume oxygen-by-difference is valid when the sample contains additional unentered elements.
Result interpretation
Use the empirical formula as the simplest ratio. Use the molecular formula only when the molar mass is reliable enough to support the multiplier.