The concentration characterizes the composition of a mixture with respect to the volume of the mixture. There are mass, amount, number and volume concentrations. Related and within the scope of this tag are normality, molality, mole fraction/ratio, mass fraction/ratio.

The concentration characterizes the composition of a mixture with respect to the volume of the mixture. It is a group of four quantities: mass, amount, number and volume concentration. It is also usually used as the short form for amount (of substance) concentration.

Related and within the scope of this tag are normality, molality, mole fraction/ratio, mass fraction/ratio.

Mass concentration

  • Mass of a constituent divided by the volume of the mixture.
  • Symbol: $\rho, \gamma$
  • SI Unit: $\rho_i = \frac{m_i}{V} = \mathrm{\frac{kg}{m^3}}$
  • Common units: $\mathrm{\frac{g}{L}}$

Amount concentration

  • Amount of a constituent divided by the volume of the mixture. For entities $B$ it is often denoted as $[B]$
  • Synonyms amount-of-substance concentration, substance concentration, molar concentration, molarity
  • Symbol: $c$
  • SI Unit: $\phi_i = \frac{n_i}{V} = \mathrm{\frac{mol}{m^3}}$
  • Common units: $\mathrm{\frac{mol}{L}}=\mathrm{\frac{mmol}{mL}}=\mathrm{\frac{mol}{dm^3}}$ (Often denoted as $M$)

Number concentration

  • Number of entities of a constituent in a mixture divided by the volume of the mixture.
  • Symbol: $C, n$
  • SI Unit:$\phi_i = \frac{N_i}{V} = \mathrm{m^{-3}}$

Volume concentration

  • Volume of a constituent of a mixture divided by the sum of volumes of all constituents prior to mixing.
  • Synonym: volume fraction
  • Symbol: $\phi$
  • SI Umit: (dimensionless) $\phi_i = \frac{V_i}{V} = \mathrm{1}$
  • Common Units: $\mathrm{\frac{L}{L}}$, or expressed as numbers $0.5$ or $50\%$

Related Normality

  • Entity corresponding to the transfer of a $\ce{H+}$ ion in a neutralization reaction, of an electron in a redox reaction, or to a magnitude of charge number equal to 1 in ions.
  • Examples: $\ce{\frac12 H2SO4, \frac15 KMnO4, \frac13 Fe^{3+}}$
  • Synonyms: equivalent concentration, equivalent entity
  • IUPAC discourages the use of this

Related Molality

  • Amount of entities of a solute divided by the mass of the solvent
  • Symbol: $m, b$
  • SI Unit: $b_i = \frac{n_i}{m_{\mathrm{solvent}}} = \mathrm{\frac{mol}{kg}}$

Related Mole fraction

  • Amount of a constituent divided by the total amount of all constituents in the mixture.
  • Synonym: Amount fraction
  • Symbol: $x$ ($y$ for gaseous mixtures)
  • SI Unit: (dimensionless) $x_i = \frac{n_i}{n} = \mathrm{1}$
  • Common units: $\mathrm{\frac{mol}{mol}}$. parts per million/billion/trillion (ppm/b/t)
  • Mole ratio: $r_i = \frac{n_i}{n - n_i}$

Related Number fraction

  • the number of entities of one constituent divided by the total number of entities in the mixture.
  • equal to mole fraction

Related Mass fraction

  • Mass of a constituent divided by the total mass of all constituents in the mixture.
  • Symbol: $w$
  • SI Umit: (dimensionless) $w_i = \frac{m_i}{m} = \mathrm{1}$
  • Common units: $\mathrm{\frac{kg}{kg}}$. parts per million/billion/trillion (ppm/b/t)
  • Mass ratio: $\zeta_i = \frac{m_i}{m - m_i}$

Further reading

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