Concentration
In
Etymology
Concentration-, concentratio, action or an act of coming together at a single place, bringing to a common center, was used in post-classical Latin in 1550 or earlier, similar terms attested in Italian (1589), Spanish (1589), English (1606), French (1632).[2]
Qualitative description
Often in informal, non-technical language, concentration is described in a
Concentrations are often called levels, reflecting the mental
Quantitative notation
There are four quantities that describe concentration:
Mass concentration
The mass concentration is defined as the mass of a constituent divided by the volume of the mixture :
The SI unit is kg/m3 (equal to g/L).
Molar concentration
The molar concentration is defined as the amount of a constituent (in moles) divided by the volume of the mixture :
The SI unit is mol/m3. However, more commonly the unit mol/L (= mol/dm3) is used.
Number concentration
The number concentration is defined as the number of entities of a constituent in a mixture divided by the volume of the mixture :
The SI unit is 1/m3.
Volume concentration
The volume concentration (not to be confused with volume fraction[3]) is defined as the volume of a constituent divided by the volume of the mixture :
Being dimensionless, it is expressed as a number, e.g., 0.18 or 18%; its unit is 1.
There seems to be no standard notation in the English literature. The letter used here is normative in German literature (see Volumenkonzentration).
Related quantities
Several other quantities can be used to describe the composition of a mixture. These should not be called concentrations.[1]
Normality
Normality is defined as the molar concentration divided by an equivalence factor . Since the definition of the equivalence factor depends on context (which reaction is being studied), the
Molality
The molality of a solution is defined as the amount of a constituent (in moles) divided by the mass of the solvent (not the mass of the solution):
The SI unit for molality is mol/kg.
Mole fraction
The mole fraction is defined as the amount of a constituent (in moles) divided by the total amount of all constituents in a mixture :
The SI unit is mol/mol. However, the deprecated parts-per notation is often used to describe small mole fractions.
Mole ratio
The mole ratio is defined as the amount of a constituent divided by the total amount of all other constituents in a mixture:
If is much smaller than , 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
The mass fraction is the fraction of one substance with mass to the mass of the total mixture , defined as:
The SI unit is kg/kg. However, the deprecated parts-per notation is often used to describe small mass fractions.
Mass ratio
The mass ratio is defined as the mass of a constituent divided by the total mass of all other constituents in a mixture:
If is much smaller than , 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.
Dependence on volume and temperature
Concentration depends on the variation of the volume of the solution with temperature, due mainly to thermal expansion.
Concentration type | Symbol | Definition | SI unit | other unit(s) |
---|---|---|---|---|
mass concentration | or | kg/m3 | g/100mL (= g/dL) | |
molar concentration | mol/m3 | M (= mol/L) | ||
number concentration | 1/m3 | 1/cm3 | ||
volume concentration | m3/m3 | |||
Related quantities | Symbol | Definition | SI unit | other unit(s) |
normality | mol/m3 | M (= mol/L) | ||
molality | mol/kg | m | ||
mole fraction | mol/mol | ppm, ppb, ppt | ||
mole ratio | mol/mol | ppm, ppb, ppt | ||
mass fraction | kg/kg | ppm, ppb, ppt | ||
mass ratio | kg/kg | ppm, ppb, ppt | ||
volume fraction | m3/m3 | ppm, ppb, ppt |
See also
- Dilution ratio – Change in concentration when mixing two liquids
- Dose concentration– Ratio of part of a mixture to the whole
- Serial dilution – Step-wise dilution of a substance in solution
- Wine/water mixing problem
- Standard state § Solutes
References
- ^
- ^ "concentration". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
External links
- Media related to Concentration (chemistry) at Wikimedia Commons