Editing Concentration (section)

==Related quantities==

Several other quantities can be used to describe the composition of a mixture. These should '''not''' be called concentrations.<ref name="goldbook" />

===Normality===
{{main|Normality (chemistry)}}

Normality is defined as the molar concentration <math>c_i</math> divided by an equivalence factor <math>f_\mathrm{eq}</math>. Since the definition of the equivalence factor depends on context (which reaction is being studied), the [[IUPAC|International Union of Pure and Applied Chemistry]] and [[NIST|National Institute of Standards and Technology]] discourage the use of normality.

===Molality===
{{main|Molality}}{{Distinguish|Molarity}}
The molality of a solution <math>b_i</math> is defined as the amount of a constituent <math>n_i</math> (in moles) divided by the mass of the solvent <math>m_\mathrm{solvent}</math> ('''not''' the mass of the solution):

:<math>b_i = \frac{n_i}{m_\mathrm{solvent}}.</math>

The SI unit for molality is mol/kg.

===Mole fraction===
{{main|Mole fraction}}

The mole fraction <math>x_i</math> is defined as the amount of a constituent <math>n_i</math> (in moles) divided by the total amount of all constituents in a mixture <math>n_\mathrm{tot}</math>:

:<math>x_i = \frac {n_i}{n_\mathrm{tot}}.</math>

The SI unit is mol/mol. However, the deprecated [[parts-per notation]] is often used to describe small mole fractions.

===Mole ratio===
{{main|Mixing ratio}}

The mole ratio <math>r_i</math> is defined as the amount of a constituent <math>n_i</math> divided by the total amount of all ''other'' constituents in a mixture:

:<math>r_i = \frac{n_i}{n_\mathrm{tot}-n_i}.</math>

If <math>n_i</math> is much smaller than <math>n_\mathrm{tot}</math>, the mole ratio is almost identical to the mole fraction.

The SI unit is mol/mol. However, the deprecated parts-per notation is often used to describe small mole ratios.

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

The mass fraction <math>w_i</math> is the fraction of one substance with mass <math>m_i</math> to the mass of the total mixture <math>m_\mathrm{tot}</math>, defined as:

:<math>w_i = \frac {m_i}{m_\mathrm{tot}}.</math>

The SI unit is kg/kg. However, the deprecated parts-per notation is often used to describe small mass fractions.

===Mass ratio===
{{main|Mixing ratio}}

The mass ratio <math>\zeta_i</math> is defined as the mass of a constituent <math>m_i</math> divided by the total mass of all ''other'' constituents in a mixture:

:<math>\zeta_i = \frac{m_i}{m_\mathrm{tot}-m_i}.</math>

If <math>m_i</math> is much smaller than <math>m_\mathrm{tot}</math>, the mass ratio is almost identical to the mass fraction.

The SI unit is kg/kg. However, the deprecated parts-per notation is often used to describe small mass ratios.