In chemistry, the mass fraction of a substance within a mixture is the ratio
It is one way of expressing the composition of a mixture in a dimensionless size; mole fraction (percentage by moles, mol%) and volume fraction (percentage by volume, vol%) are others.
When the prevalences of interest are those of individual chemical elements, rather than of compounds or other substances, the term mass fraction can also refer to the ratio of the mass of an element to the total mass of a sample.
In these contexts an alternative term is mass percent composition.
The mass fraction of an element in a compound can be calculated from the compound's empirical formula[2] or its chemical formula.
[3] Percent concentration does not refer to this quantity.
This improper name persists, especially in elementary textbooks.
In biology, the unit "%" is sometimes (incorrectly) used to denote mass concentration, also called mass/volume percentage.
This is incorrect because the unit "%" can only be used for dimensionless quantities.
The very ambiguous terms percent solution and percentage solutions with no other qualifiers continue to occasionally be encountered.
In alloys, especially those of noble metals, the term fineness is used for the mass fraction of the noble metal in the alloy.
The mass fraction is independent of temperature.
The mass fraction of a component in a solution is the ratio of the mass concentration of that component ρi (density of that component in the mixture) to the density of solution
is the average molar mass of the mixture.
Replacing the expression of the molar-mass products, In a spatially non-uniform mixture, the mass fraction gradient gives rise to the phenomenon of diffusion.