Concentration (chemistry)

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According to DIN 1310 , the concentration is a content that is based on the volume of the mixture . The concentration therefore indicates how much of a substance (the solvate under consideration ) is present in a comparison volume of the mixture (solvate and solvent ). Solvate and solvent, various states of matter have and the mixture can be polyphase; then solvate and solvent can even be made 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 themselves be mixtures. The concentration of a substance in the mixture is temperature-dependent due to different expansion coefficients .

Very low concentrations are referred to as 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 information:

  • The amount of substance concentration 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 molar concentration; Here the molar unit of mole relates to equivalent particles, i.e. to virtual fragments of real particles, in order to take their chemical valency into account, unit of measure l mol / l, out of date val / l.
  • The mass concentration : Defined as the mass of the solvate per volume of the 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 share, which is related to the sum of the volumes of all shares.
  • The particle density or particle concentration : Defined as the number of particles or particles per volume of the mixture, unit 1 / l.

These terms for related quantities as quotients of mass, volume, amount of substance or number of particles of a substance in relation to the volume of the mixture in which the substance is, follow the standard DIN 5485 naming principles for physical quantities; Word compositions with adjectives and basic words.

Often the term concentration is not used properly in the sense of a general content specification , so that it remains unclear whether substance concentration, mass concentration or volume concentration or even a proportion is meant. An example of this is when in biochemistry occasionally a concentration is 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 . A solution of 1% (m / V) therefore contains 10 g / l (mostly of a solid), even if the density after the dissolution process is usually greater than 1 g / ml.

Individual evidence

  1. Entry on concentration. In: Römpp Online . Georg Thieme Verlag, accessed on November 1, 2014.
  2. Entry on concentration . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.C01222 Version: 2.3.
  3. ^ Entry Spiegel on, accessed on November 3, 2016.
  4. Entry on equivalent entity . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.E02192 Version: 2.3.