Mole Fraction

x_1 = \frac{n_1}{n_1 + n_2}

Worked example: 1 mol solute + 9 mol solvent → x1 = 0.1. Press Try an example to run it live, then adjust anything.

Enter your known values, leave one input blank, and solves for the missing one. Tap a variable’s symbol to see what it means, with a typical value. Change any unit and the answer follows.

Where Mole Fraction fits

Missing an input?

In this toolkit

Ways to express concentration6 formulas

Here the solver did the work. Could you?

Partial pressures →

Grade 12Grade 12 Chemistry

Test your skills in the Exam Room: new numbers every attempt. Free lessons for students, no sign-up, just pure learning.

See your Report Card

Learning zone

Mole Fraction explained

The mole fraction asks the simplest possible concentration question: of every mole of particles in the mixture, what share belongs to component 1? Dissolve 1.00 mol of ethylene glycol in 9.00 mol of water and x₁ = 1.00/(1.00 + 9.00) = 0.100: no units, no temperature dependence, and all the mole fractions in a mixture always sum to exactly 1.

This makes x the natural currency of vapor-pressure laws: Raoult's law and Dalton's law are both written in mole fractions, and gas mixtures are routinely quoted this way. Dry air is x ≈ 0.78 nitrogen and 0.21 oxygen. Solving the definition backwards for n₁ or n₂ requires x strictly between 0 and 1, since a pure component (x = 1) carries no information about how much solvent could be present.

Mole Fraction formula

x_1 = \frac{n_1}{n_1 + n_2}

Where

$x_1$ = Mole fraction of solute
$n_1$ = Amount of solute (mol)
$n_2$ = Amount of solvent (mol)

In this toolkit

Ways to express concentration

6 formulasMolarity, molality, mass percent, mole fraction, normality and the dilution equation — six answers to “how much solute is in there?”

Revised 16 October 2026

Cite this page

formula.expert. (2026, October 16). Mole Fraction Formula & Calculator. https://formula.expert/solvers/mole-fraction

https://formula.expert/solvers/mole-fraction