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 use “Copy URL” to copy a shareable URL. 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
Frequently asked questions
Can I mix percent and gram entries?
No. Use one input basis for every row. Percentages use a 100 g assumption; grams use the masses you enter.
What if combustion gives a negative oxygen mass?
Check the C/H/O assumption and the measurements. A negative mass-balance result does not confirm a formula; a true zero can be valid for a sample without oxygen.
What does a share link reproduce?
It restores the valid calculation snapshot: inputs and settings are recalculated. A candidate remains a candidate rather than becoming a confirmed formula.
What if the hydrate water number is not an integer?
Review the raw x and the tolerance. Fractional hydrates can exist, so this integer-hydrate model leaves the formula unconfirmed when x is not within tolerance of an integer.
Is a molecular formula always determined?
No. The target molar mass must match an integer multiple of the empirical mass within the selected tolerance. A formula does not identify a structure or substance name.
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.