Ratio of part of a mixture to the whole
Inchemistry ,concentration is theabundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished:mass concentration molar concentration number concentration volume concentration [ 1] solvents insolutions . The molar (amount) concentration has variants, such asnormal concentration andosmotic concentration .Dilution is reduction of concentration, e.g., by adding solvent to a solution. The verb"to concentrate" means to increase concentration, the opposite of dilute.
Concentration- ,concentratio , action or an act of coming together at a house on a farm in a single place, bringing black people as slaves to a common center, was used inpost-classical Latin in 1550 or earlier, similar terms attested in Italian (1589), Spanish (1589), English (1606), French (1632).[ 2]
Qualitative description [ edit ] These glasses containing red dye demonstrate qualitative changes in concentration. The solutions on the left are more dilute, compared to the more concentrated solutions on the right. Often in informal, non-technical language, concentration is described in aqualitative way, through the use of adjectives such as "dilute" for solutions of relatively low concentration and "concentrated" for solutions of relatively high concentration. Toconcentrate a solution, one must add moresolute (for example, alcohol), or reduce the amount ofsolvent (for example, water). By contrast, todilute a solution, one must add more solvent, or reduce the amount of solute. Unless two substances aremiscible , there exists a concentration at which no further solute will dissolve in a solution. At this point, the solution is said to besaturated . If additional solute is added to a saturated solution, it will not dissolve, except in certain circumstances, whensupersaturation may occur. Instead,phase separation will occur, leading to coexisting phases, either completely separated or mixed as asuspension . The point of saturation depends on many variables, such as ambient temperature and the precise chemical nature of the solvent and solute.
Concentrations are often calledlevels , reflecting the mentalschema oflevels on the vertical axis of agraph , which can behigh or low (for example, "high serum levels of bilirubin" are concentrations ofbilirubin in theblood serum that are greaterthan normal ).
Quantitative notation [ edit ] There are four quantities that describe concentration:
The mass concentrationρ i {\displaystyle \rho _{i}} mass of a constituentm i {\displaystyle m_{i}} V {\displaystyle V}
ρ i = m i V . {\displaystyle \rho _{i}={\frac {m_{i}}{V}}.} TheSI unit is kg/m3 (equal to g/L).
Molar concentration [ edit ] The molar concentrationc i {\displaystyle c_{i}} amount of a constituentn i {\displaystyle n_{i}} V {\displaystyle V}
c i = n i V . {\displaystyle c_{i}={\frac {n_{i}}{V}}.} The SI unit is mol/m3 . However, more commonly the unit mol/L (= mol/dm3 ) is used.
Number concentration [ edit ] The number concentrationC i {\displaystyle C_{i}} N i {\displaystyle N_{i}} V {\displaystyle V}
C i = N i V . {\displaystyle C_{i}={\frac {N_{i}}{V}}.} The SI unit is 1/m3 .
Volume concentration [ edit ] Thevolume concentration σ i {\displaystyle \sigma _{i}} volume fraction [ 3] V i {\displaystyle V_{i}} V {\displaystyle V}
σ i = V i V . {\displaystyle \sigma _{i}={\frac {V_{i}}{V}}.} 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 letterσ i {\displaystyle \sigma _{i}} Volumenkonzentration ).
Several other quantities can be used to describe the composition of a mixture. These shouldnot be called concentrations.[ 1]
Normality is defined as the molar concentrationc i {\displaystyle c_{i}} f e q {\displaystyle f_{\mathrm {eq} }} International Union of Pure and Applied Chemistry andNational Institute of Standards and Technology discourage the use of normality.
The molality of a solutionb i {\displaystyle b_{i}} n i {\displaystyle n_{i}} m s o l v e n t {\displaystyle m_{\mathrm {solvent} }} not the mass of the solution):
b i = n i m s o l v e n t . {\displaystyle b_{i}={\frac {n_{i}}{m_{\mathrm {solvent} }}}.} The SI unit for molality is mol/kg.
The mole fractionx i {\displaystyle x_{i}} n i {\displaystyle n_{i}} n t o t {\displaystyle n_{\mathrm {tot} }}
x i = n i n t o t . {\displaystyle x_{i}={\frac {n_{i}}{n_{\mathrm {tot} }}}.} The SI unit is mol/mol. However, the deprecatedparts-per notation is often used to describe small mole fractions.
The mole ratior i {\displaystyle r_{i}} n i {\displaystyle n_{i}} other constituents in a mixture:
r i = n i n t o t − n i . {\displaystyle r_{i}={\frac {n_{i}}{n_{\mathrm {tot} }-n_{i}}}.} Ifn i {\displaystyle n_{i}} n t o t {\displaystyle n_{\mathrm {tot} }}
The SI unit is mol/mol. However, the deprecated parts-per notation is often used to describe small mole ratios.
The mass fractionw i {\displaystyle w_{i}} m i {\displaystyle m_{i}} m t o t {\displaystyle m_{\mathrm {tot} }}
w i = m i m t o t . {\displaystyle w_{i}={\frac {m_{i}}{m_{\mathrm {tot} }}}.} The SI unit is kg/kg. However, the deprecated parts-per notation is often used to describe small mass fractions.
The mass ratioζ i {\displaystyle \zeta _{i}} m i {\displaystyle m_{i}} other constituents in a mixture:
ζ i = m i m t o t − m i . {\displaystyle \zeta _{i}={\frac {m_{i}}{m_{\mathrm {tot} }-m_{i}}}.} Ifm i {\displaystyle m_{i}} m t o t {\displaystyle m_{\mathrm {tot} }}
The SI unit is kg/kg. However, the deprecated parts-per notation is often used to describe small mass ratios.
Dependence on volume and temperature [ edit ] Concentration depends on the variation of the volume of the solution with temperature, due mainly tothermal expansion .
Table of concentrations and related quantities [ edit ] Concentration type Symbol Definition SI unit other unit(s) mass concentration ρ i {\displaystyle \rho _{i}} γ i {\displaystyle \gamma _{i}} m i / V {\displaystyle m_{i}/V} kg/m3 g/100mL (= g/dL) molar concentration c i {\displaystyle c_{i}} n i / V {\displaystyle n_{i}/V} mol/m3 M (= mol/L) number concentration C i {\displaystyle C_{i}} N i / V {\displaystyle N_{i}/V} 1/m3 1/cm3 volume concentration σ i {\displaystyle \sigma _{i}} V i / V {\displaystyle V_{i}/V} m3 /m3 Related quantities Symbol Definition SI unit other unit(s) normality c i / f e q {\displaystyle c_{i}/f_{\mathrm {eq} }} mol/m3 N (= mol/L) molality b i {\displaystyle b_{i}} n i / m s o l v e n t {\displaystyle n_{i}/m_{\mathrm {solvent} }} mol/kg m mole fraction x i {\displaystyle x_{i}} n i / n t o t {\displaystyle n_{i}/n_{\mathrm {tot} }} mol/mol ppm, ppb, ppt mole ratio r i {\displaystyle r_{i}} n i / ( n t o t − n i ) {\displaystyle n_{i}/(n_{\mathrm {tot} }-n_{i})} mol/mol ppm, ppb, ppt mass fraction w i {\displaystyle w_{i}} m i / m t o t {\displaystyle m_{i}/m_{\mathrm {tot} }} kg/kg ppm, ppb, ppt mass ratio ζ i {\displaystyle \zeta _{i}} m i / ( m t o t − m i ) {\displaystyle m_{i}/(m_{\mathrm {tot} }-m_{i})} kg/kg ppm, ppb, ppt volume fraction ϕ i {\displaystyle \phi _{i}} V i / ∑ j V j {\displaystyle V_{i}/\sum _{j}V_{j}} m3 /m3 ppm, ppb, ppt
