Massafraktioksi

Massafraktioksi, or mass fraction, is a dimensionless quantity used to describe the composition of a mixture. It represents the portion of the total mass that is made up by a given component.

Definition and notation

The mass fraction of component i is defined as w_i = m_i / m_total, where m_i is the mass of component i and m_total is the total mass of the mixture. The mass fractions of all components sum to 1 (or 100% when expressed as a percentage). In practice, w_i is often written simply as w_i, and mass percent is 100 times the mass fraction.

Relation to other concentration measures

Mass fraction is related to molar fraction x_i by the equation w_i = (x_i M_i) / sum_j (x_j M_j), where M_i is the molar mass of component i. Conversely, x_i = (w_i / M_i) / sum_j (w_j / M_j). Mass fraction is independent of the amount of sample and is particularly useful for expressing the composition of solid, liquid, and gaseous mixtures.

Applications

Mass fraction is widely used in chemical engineering, materials science, environmental science, and pharmaceutics to characterize mixtures such as alloys, solutions, and fuels. It supports calculations of properties that depend on composition, such as phase behavior, quality control, and material design.

Examples

In a solution containing 2 g of solute and 98 g of solvent, the mass fraction of solute is w_solute = 0.02 and of solvent is w_solvent = 0.98. Expressed as a percentage, these are 2% and 98%, respectively.

Limitations

Mass fraction provides a mass-based view of composition and does not directly convey concentration per volume or the number of moles. For such information, molar fraction or molarity may be more appropriate.