How this calculation works
Convert element masses to moles and ratios to the smallest amount. Search bounded integer multipliers, reduce by a common divisor and choose the smallest fitting atom count under the entered mass-percentage tolerance.
Element moles = element mass / atomic weight; search small whole-number ratios and compare fitted mass percentagesA worked example
Mass percentages C 40, H 6.7 and O 53.3 fit the empirical candidate CH2O under the illustrated tolerance. A molecular mass near 180.156 g/mol supports six empirical units, giving C6H12O6.
Good to know
A bounded composition fit is not chemical identification or structural proof. Alternative formulas can fit. Uses rounded conventional atomic weights; no charge, isotopic composition, purity or hydration inference.
Reference: OpenStax: empirical and molecular formulas (opens in a new tab) ↗
Mass percentages are not atom percentages
Different elements have different atomic weights. Equal masses therefore do not mean equal atom counts. Dividing by each atomic weight moves the measured composition onto a mole-ratio basis.
Percentage mode checks that the entries total 100 within the stated input tolerance. Mass mode accepts a common arbitrary mass scale because multiplying every entry by the same factor leaves the ratios unchanged.
The colligative solution properties calculator adds calculate ideal freezing depression and boiling elevation from molality and entered particle factors, keeping solvent mass distinct from solution mass. The limiting reactant theoretical yield calculator adds check element balance, convert pure reactant masses to available reaction extent and calculate theoretical products, leftovers and measured percent yield.
A candidate must reproduce the measured composition
Rounding each raw mole ratio immediately can erase a fractional relationship. The bounded search instead tries multipliers and checks the resulting formula against the original mass percentages.
The reported residual is the maximum percentage-point difference across elements. A numerical fit does not establish uniqueness; the method favors a simple fitting candidate rather than claiming exhaustive chemical identification.
Molecular mass supplies a separate constraint
An empirical formula states the smallest modeled atom ratio. A molecular formula can be an integer multiple of that ratio, so a separately measured molecular mass can constrain the multiplier.
Its tolerance is relative percent, unlike the composition residual measured in percentage points. If no whole multiple matches, the page reports inconsistency rather than forcing an arbitrary molecular formula.
Use the result with the next measurement
The colligative solution properties calculator requires a supplied molar mass. A composition candidate alone does not establish the actual molecular mass or the effective particle count in solution.
A bounded composition fit is not chemical identification or structural proof. Alternative formulas can fit. Uses rounded conventional atomic weights; no charge, isotopic composition, purity or hydration inference.
A few questions, answered
Does the fitted formula identify a compound?
No, composition alone does not determine structure or identity.
What is the search limit?
Multipliers 1–12 and at most 1,000 atoms of any element.
Are the two tolerances the same?
No, composition uses percentage points; molecular mass uses relative percent.