Mole Fraction
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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 of solute
- = Amount of solute
- = Amount of solvent
- Mole fraction of solute — Raoult's Law, Partial Pressure from Mole Fraction
- Amount of solute — Molarity (C = n/V), Molality (b = n/m)
- Amount of solvent — Ideal Gas Law, Moles from Mass (n = m/M)