Concentration

In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture.

[1] The concentration can refer to any kind of chemical mixture, but most frequently refers to solutes and solvents in solutions.

Dilution is reduction of concentration, e.g. by adding solvent to a solution.

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).

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.

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.

Concentrations are often called levels, reflecting the mental schema of levels on the vertical axis of a graph, which can be high or low (for example, "high serum levels of bilirubin" are concentrations of bilirubin in the blood serum that are greater than normal).

: The SI unit is kg/m3 (equal to g/L).

(in moles) divided by the volume of the mixture

is defined as the number of entities of a constituent

: 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.

used here is normative in German literature (see Volumenkonzentration).

Several other quantities can be used to describe the composition of a mixture.

[1] Normality is defined as the molar concentration

Since the definition of the equivalence factor depends on context (which reaction is being studied), the International Union of Pure and Applied Chemistry and National Institute of Standards and Technology discourage the use of normality.

(in moles) divided by the mass of the solvent

(not the mass of the solution): The SI unit for molality is mol/kg.

(in moles) divided by the total amount of all constituents in a mixture

However, the deprecated parts-per notation is often used to describe small mole fractions.

divided by the total amount of all other constituents in a mixture: If

However, the deprecated parts-per notation is often used to describe small mole ratios.

However, the deprecated parts-per notation is often used to describe small mass fractions.

divided by the total mass of all other constituents in a mixture: If

However, the deprecated parts-per notation is often used to describe small mass ratios.

Concentration depends on the variation of the volume of the solution with temperature, due mainly to thermal expansion.