Editing Concentration (section)

==Quantitative notation==

There are four quantities that describe concentration:

===Mass concentration===
{{main|Mass concentration (chemistry)}}

The mass concentration <math>\rho_i</math> is defined as the [[mass]] of a constituent <math>m_i</math> divided by the volume of the mixture <math>V</math>:

:<math>\rho_i = \frac {m_i}{V}.</math>

The [[International System of Units|SI unit]] is kg/m<sup>3</sup> (equal to g/L).

===Molar concentration===
{{main|Molar concentration}}

The molar concentration <math>c_i</math> is defined as the [[amount of substance|amount]] of a constituent <math>n_i</math> (in moles) divided by the volume of the mixture <math>V</math>:

:<math>c_i = \frac {n_i}{V}.</math>

The SI unit is mol/m<sup>3</sup>. However, more commonly the unit mol/L (= mol/dm<sup>3</sup>) is used.

===Number concentration===
{{main|Number concentration}}

The number concentration <math>C_i</math> is defined as the number of entities of a constituent <math>N_i</math> in a mixture divided by the volume of the mixture <math>V</math>:

:<math>C_i = \frac{N_i}{V}.</math>

The SI unit is 1/m<sup>3</sup>.

===Volume concentration===

The '''volume concentration''' <math>\sigma_i</math> (not to be confused with [[volume fraction]]<ref name="goldbook2">{{GoldBookRef | file = V06643 | title = volume fraction}}</ref>) is defined as the volume of a constituent <math>V_i</math> divided by the volume of the mixture <math>V</math>:

:<math>\sigma_i = \frac {V_i}{V}.</math>

Being dimensionless, it is expressed as a number, e.g., 0.18 or 18%.

There seems to be no standard notation in the English literature. The letter <math>\sigma_i</math> used here is normative in German literature (see [[:de:Volumenkonzentration|Volumenkonzentration]]).