Mass fraction In chemistry, the mass fraction is the ratio of one substance with mass to the mass of the total mixture , defined asThe sum of all the mass fractions is equal to 1:Mass fraction can also be expressed, with a denominator of 100, as percentage by weight (wt%). 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. For elemental analysis, mass fraction (or "mass percent composition") can also refer to the ratio of the mass of one element to the total mass of a compound. It can be calculated for any compound using its empirical formula. or its chemical formula Dimensionless Ratio Wikipedia http://dbpedia.org/page/Mass_fraction_(chemistry) ODM2 Units Type Controlled Vocabulary ODM2 Working Group A vocabulary for describing the type of the Unit or the more general quantity that the Unit represents.