= Mass fraction
{title2=$w_i=m_i/\sum_j m_j$}
The <mass fraction> of component $i$ in a <mixture> is $w_i=m_i/\sum_jm_j$. 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 $5$ grams of solute and $95$ grams of solvent has solute mass fraction $0.05$, 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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