Concentration Information
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration.[1] The term concentration can be applied to any kind of chemical mixture, but most frequently it refers to solutes in homogeneous solutions.
Contents |
Qualitative description
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 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 either coexisting phases or a suspension. The point of saturation depends on many variables such as ambient temperature and the precise chemical nature of the solvent and solute.
Quantitative notation
There are four quantities that describe concentration:
Mass concentration
Main article: Mass concentration (chemistry)The mass concentration ρi is defined as the mass of a constituent mi divided by the volume of the mixture V:
The SI-unit is kg/m3.
Molar concentration
Main article: Molar concentrationThe molar concentration ci is defined as the amount of a constituent ni divided by the volume of the mixture V:
The SI-unit is mol/m3. However, more commonly the unit mol/L is used.
Number concentration
Main article: Number concentrationThe number concentration Ci is defined as the number of entities of a constituent Ni in a mixture divided by the volume of the mixture V:
The SI-unit is 1/m3.
Volume concentration
Main article: Volume concentrationThe volume concentration φi (also called volume fraction) is defined as the volume of a constituent Vi divided by the volume of all consituents of the mixture V prior to mixing:
The SI-unit is m3/m3.
Related Quantities
Several other quantities can be used to describe the composition of a mixture. Note that these should not be called concentrations.
Normality
Main article: Normality (chemistry)Normality is defined as the molar concentration ci divided by an equivalence factor feq. Since the definition of the equivalence factor may not be unequivocal, IUPAC and NIST discourage the use of normality.
Molality
Main article: MolalityThe molality of a solution mi is defined as the amount of a constituent ni divided by the mass of the solvent msolvent (not the mass of the solution):
The SI-unit for molality is mol/kg.
Mole fraction
Main article: Mole fractionThe mole fraction xi is defined as the amount of a constituent ni divided by the total amount of all constituents in a mixture ntot:
The SI-unit is mol/mol. However, the deprecated parts-per notation is often used to describe small mole fractions.
Mole ratio
Main article: Mixing ratioThe mole ratio ri is defined as the amount of a constituent ni divided by the total amount of all other constituents in a mixture:
If ni is much smaller than ntot, 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 article: Mass fraction (chemistry)The mass fraction wi is the fraction of one substance with mass mi to the mass of the total mixture mtot, defined as:
The SI-unit is kg/kg. However, the deprecated parts-per notation is often used to describe small mass fractions.
Mass ratio
Main article: Mixing ratioThe mass ratio ζi is defined as the mass of a constituent mi divided by the total mass of all other constituents in a mixture:
If mi is much smaller than mtot, 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.
Table of concentrations and related quantities
| Concentration type | Symbol | Definition | SI-unit | other unit(s) |
|---|---|---|---|---|
| mass concentration | ρi or γi | mi / V | kg/m3 | g/100mL (=g/dL) |
| molar concentration | ci | ni / V | mol/m3 | M (=mol/L) |
| number concentration | Ci | Ni / V | 1/m3 | 1/cm3 |
| volume concentration | φi | Vi / V | m3/m3 | |
| Related quantities | Symbol | Definition | SI-unit | other unit(s) |
| normality | ci / feq | mol/m3 | M (=mol/L) | |
| molality | mi | ni / msolvent | mol/kg | |
| mole fraction | xi | ni / ntot | mol/mol | ppm, ppb, ppt |
| mole ratio | ri | ni / (ntot − ni) | mol/mol | ppm, ppb, ppt |
| mass fraction | wi | mi / mtot | kg/kg | ppm, ppb, ppt |
| mass ratio | ζi | mi / (mtot − mi) | kg/kg | ppm, ppb, ppt |
See also
- Serial dilution
- Practical examples of 1 and 2 normal acids in biochemistry
References
- ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "concentration".
|
||||||||||||||
Categories: Analytical chemistry | Chemical properties
|
)
500px x 500px | 32.50kB
[source page]
on e Bay on Amazon on Amazon in addition to The Tonight Show Ed Mc Mahon emceed a number of television game shows including Concentration in 1969
Sun, 05 Sep 2010 18:23:47 GMT+00:00
Science 2.0 But in the initial work, the concentration of the structures in the solution was low, so the overall efficiency of the device the amount of electricity ...