Concentration

According to DIN 1310, the concentration is a content information which is related to the volume of the mixture. The concentration thus indicates how much of a substance (the solvate under consideration) is present in a reference volume of the mixture (solvate and solvent). Solvate and solvent can have different states of aggregation and thus the mixture can be multiphase; then solvate and solvent can even be of the same substance. In addition to the solvate under consideration, for which the concentration is given, other solvates may also be present. The solvent and the solvate can therefore themselves be mixtures. The concentration of a substance in the mixture is temperature-dependent due to different expansion coefficients.

Very low concentrations are called traces (for differentiation see trace element).

In medicine there is also the term level for the concentration of a substance in the blood (whole blood level), plasma (plasma level) or serum (serum level).

Concentration data:

• The concentration of the amount of substance or molarity (to be confused with molality): amount of substance of the solvate per volume of the mixture, unit of measurement mol/l.
• The equivalent concentration or normality is a special form of the substance quantity concentration; here the substance quantity unit mole refers to equivalent particles, i.e. to virtual fractions of real particles, in order to take into account their chemical valency, unit of measurement mol/l, outdated val/l.
• Mass concentration: Defined as mass of solvate per volume of mixture, unit g/l.
• The volume concentration: defined as the volume of the solvate per volume of the mixture, unit l/l; not equivalent to the volume fraction, which is related to the sum of the volumes of all fractions.
• The particle density or particle concentration: Defined as the number of particles or particulates per volume of the mixture, unit 1/l.

These designations for related quantities as quotients of mass, volume, quantity of substance or number of particles of a substance related to the volume of the mixture in which the substance is contained follow the standard DIN 5485 Naming principles for physical quantities; word combinations with property and basic words.

Often the term concentration is not used appropriately in the sense of a general indication of content, so that it remains unclear whether substance quantity concentration, mass concentration or volume concentration or even a proportion is meant. An example of this is when In biochemistry, a concentration is occasionally given in the form of a mass fraction in liquids with the percentage % (m/V), whereby a density of 1 g/ml is assumed for the volume as an approximation. A solution of 1 % (m/V) thus contains 10 g/l (mostly of a solid), even if the density after the dissolution process is mostly greater than 1 g/ml.