Concentration
In chemistry, concentration is the measure
of how much of a given substance there is
mixed with another substance. This can apply
to any sort of chemical mixture, but most fre-
quently the concept is limited to homogen-
eous solutions, where it refers to the amount
of solute in the solvent.
To concentrate a solution, one must add
more solute, or reduce the amount of solvent
(for instance, by selective evaporation). 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 fur-
ther solute will dissolve in a solution. At this
point, the solution is said to be saturated. If
additional solute is added to a saturated solu-
tion, it will not dissolve (except in certain cir-
cumstances, when supersaturation may oc-
cur). Instead, phase separation will occur,
leading to either coexisting phases or a sus-
pension. The point of saturation depends on
many variables such as ambient temperature
and the precise chemical nature of the
solvent and solute.
Analytical concentration includes all the
forms of that substance in the solution.
Qualitative description
These glasses containing red dye demon-
strate 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 concen-
tration and of others like "concentrated" for
solutions of relatively high concentration.
Those terms relate the amount of a substance
in a mixture to the observable intensity of ef-
fects or properties caused by that substance.
For example, a practical rule is that the more
concentrated a chromatic solution is, the
more intensely colored it is (usually).
Quantitative notation
For scientific or technical applications, a
qualitative account of concentration is almost
never sufficient;