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Dalam ilmu kimia, konsentrasi adalah ukuran yang menggambarkan banyaknya zat di dalam suatu campuran dibagi dengan volume total campuran tersebut. Terdapat empat macam deskripsi kuantitatif konsentrasi, yaitu konsentrasi massa, konsentrasi molar, konsentrasi jumlah, dan konsentrasi volume. Istilah konsentrasi dapat diterapkan untuk semua jenis campuran, tetapi paling sering digunakan untuk menggambarkan jumlah zat terlarut di dalam larutan.
Deskripsi kualitatif [sunting]
Often in informal, non-technical language, concentration is described in a qualitative way, through the use of adjectives such as "dilute" for solutions of relatively low concentration and "concentrated" for solutions of relatively high concentration. To concentrate a solution, one must add more solute (for example, alcohol), or reduce the amount of solvent (for example, water). By contrast, to dilute a solution, one must add more solvent, or reduce the amount of solute. Unless two substances are fully miscible there exists a concentration at which no further solute will dissolve in a solution. At this point, the solution is said to be saturated. If additional solute is added to a saturated solution, it will not dissolve, except in certain circumstances, when supersaturation may occur. Instead, phase separation will occur, leading to coexisting phases, either completely separated or mixed as a suspension. The point of saturation depends on many variables such as ambient temperature and the precise chemical nature of the solvent and solute.
Notasi kuantitatif [sunting]
There are four quantities that describe concentration:
Konsentrasi massa [sunting]
The mass concentration is defined as the mass of a constituent divided by the volume of the mixture :
The SI-unit is kg/m3.
Konsentrasi molar [sunting]
The molar concentration is defined as the amount of a constituent divided by the volume of the mixture :
The SI-unit is mol/m3. However, more commonly the unit mol/L (= mol/dm3) is used.
Konsentrasi jumlah [sunting]
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.
Konsentrasi volume [sunting]
The volume concentration (also called volume fraction) is defined as the volume of a constituent divided by the volume of all constituents of the mixture prior to mixing:
The SI-unit is m3/m3.
Related quantities [sunting]
Several other quantities can be used to describe the composition of a mixture. Note that these should not be called concentrations.
Normality is defined as the molar concentration divided by an equivalence factor . Since the definition of the equivalence factor may not be unequivocal, IUPAC and NIST discourage the use of normality.
The molality of a solution is defined as the amount of a constituent divided by the mass of the solvent (not the mass of the solution):
The SI-unit for molality is mol/kg.
Fraksi mol [sunting]
The mole fraction is defined as the amount of a constituent divided by the total amount of all constituents in a mixture :
Mole ratio [sunting]
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.
Fraksi massa [sunting]
The mass fraction is the fraction of one substance with mass to the mass of the total mixture , defined as:
Mass ratio [sunting]
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.
Dependence on volume [sunting]
Concentration depends on the variation of the volume of the solution 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)|
|Related quantities||Symbol||Definition||SI-unit||other unit(s)|
|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|