The mass fraction of component in a mixture is . It is dimensionless, lies between zero and one, and the component mass fractions sum to one when all material is included.
For example, a mixture containing grams of solute and grams of solvent has solute mass fraction , or five percent by mass. This differs from a mole fraction, which counts amounts of substance, and from a mass-per-volume concentration. A temperature-dependent volume change does not by itself change the mass fraction of a closed sample.
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