Mole fraction calculator

What mole fraction tells you

IUPAC defines amount fraction, also called mole fraction, as one constituent's amount divided by the total amount of all constituents. It has no unit: mol divided by mol gives a ratio. Multiplying that fraction by 100 gives mol%.

Each component needs its own molar mass. Dividing every mass by the same value would merely reproduce mass fractions. The grams to moles calculator checks a single component; this mixture tool performs that conversion for every entry and then uses their shared total.

Worked example: equal moles, unequal masses

Enter 18.015 g H₂O and 46.069 g C₂H₆O. With the atomic weights used here, each entry represents 1 mol. Total amount is 2 mol, so each component's mole fraction is 0.5, or 50 mol%.

The mixture's total mass is 64.084 g. Water's mass fraction is 18.015 ÷ 64.084, about 0.281115, or 28.1115% by mass. Equal molecule counts do not require equal masses when the molecules have different molar masses. The example button supplies these illustrative values; it does not imply a recommended mixture.

The mean molar mass on this component basis is total grams divided by total moles: 64.084 ÷ 2 = 32.042 g/mol. This is a mixture average, not the molar mass of a newly formed compound.

Choose the components before choosing the numbers

1. Include the solvent. Omitting water or another solvent changes the denominator and makes the remaining fractions describe only a subset.
2. Use component masses. The mass of a prepared solution includes other material. Separate its composition before entering it as a pure component.
3. Keep the chemical basis consistent. Entered NaCl counts as NaCl formula units here. The tool does not estimate Na⁺ and Cl⁻ populations, ion pairing or chemical equilibria.
4. List each component once. Combine repeated amounts first. Because a formula does not distinguish isomers, entries with identical atom counts are rejected rather than silently treated as different substances.

Hydrate notation is accepted by the formula parser, but its mass remains attached to the entered formula unit. The calculator does not redistribute waters of crystallization into a solvent row. Use the actual species or component basis your problem specifies.

Mole fraction, mass fraction and molarity

Mole fraction compares moles with total moles. Mass fraction compares grams with total grams. Molarity compares moles with final solution volume, so a volume is necessary for that calculation. Neither a mole fraction nor a mass fraction alone supplies mol/L. Use the separate molarity calculator when final solution volume is known.

Zero mass is permitted for an absent component, but at least one component must have a positive mass. Changing a row's mass unit clears its number to avoid changing its meaning accidentally. Results show six significant figures; copied results retain up to eight. Measurements and atomic-weight uncertainties are not propagated.

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