In
chemistry, concentration is the
abundance
Abundance may refer to:
In science and technology
* Abundance (economics), the opposite of scarcities
* Abundance (ecology), the relative representation of a species in a community
* Abundance (programming language), a Forth-like computer progra ...
of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: ''
mass concentration'', ''
molar concentration
Molar concentration (also called molarity, amount concentration or substance concentration) is a measure of the concentration of a chemical species, in particular of a solute in a solution, in terms of amount of substance per unit volume of sol ...
'', ''
number concentration
A number is a mathematical object used to count, measure, and label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be represented in language with number words. More universally, individual numbers ca ...
'', and ''
volume concentration
In chemistry and fluid mechanics, the volume fraction φ''i'' is defined as the volume of a constituent ''V'i'' divided by the volume of all constituents of the mixture ''V'' prior to mixing:
:\phi_i = \frac
Being dimensionless, its unit is ...
''.
The concentration can refer to any kind of chemical mixture, but most frequently refers to solutes and
solvents
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
in
solution
Solution may refer to:
* Solution (chemistry), a mixture where one substance is dissolved in another
* Solution (equation), in mathematics
** Numerical solution, in numerical analysis, approximate solutions within specified error bounds
* Solutio ...
s. The molar (amount) concentration has variants, such as
normal concentration
In chemistry, the equivalent concentration or normality (N) of a solution is defined as the molar concentration ''ci'' divided by an equivalence factor ''f''eq:
:Normality =
Definition
Normality is defined as the number of gramme or mole eq ...
and
osmotic concentration
Osmotic concentration, formerly known as osmolarity, is the measure of solute concentration, defined as the number of osmoles (Osm) of solute per litre (L) of solution (osmol/L or Osm/L). The osmolarity of a solution is usually expressed as Osm/L ...
.
Etymology
The term concentration comes from the word concentrate, from the
French
French (french: français(e), link=no) may refer to:
* Something of, from, or related to France
** French language, which originated in France, and its various dialects and accents
** French people, a nation and ethnic group identified with France ...
, from con– + center, meaning “to put at the center”.
Qualitative description
Often in informal, non-technical language, concentration is described in a
qualitative
Qualitative descriptions or distinctions are based on some quality or characteristic rather than on some quantity or measured value.
Qualitative may also refer to:
*Qualitative property, a property that can be observed but not measured numericall ...
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
In chemistry, a solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. If the attractive forces between the solve ...
(for example, alcohol), or reduce the amount of
solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
(for example, water). By contrast, to dilute a solution, one must add more solvent, or reduce the amount of solute. Unless two substances are
miscible
Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). The term is most often applied to liquids but also appli ...
, there exists a concentration at which no further solute will dissolve in a solution. At this point, the solution is said to be
saturated
Saturation, saturated, unsaturation or unsaturated may refer to:
Chemistry
* Saturation, a property of organic compounds referring to carbon-carbon bonds
**Saturated and unsaturated compounds
**Degree of unsaturation
**Saturated fat or fatty acid ...
. If additional solute is added to a saturated solution, it will not dissolve, except in certain circumstances, when
supersaturation
In physical chemistry, supersaturation occurs with a solution when the concentration of a solute exceeds the concentration specified by the value of solubility at equilibrium. Most commonly the term is applied to a solution of a solid in a liq ...
may occur. Instead,
phase separation
Phase separation is the creation of two distinct phases from a single homogeneous mixture. The most common type of phase separation is between two immiscible liquids, such as oil and water. Colloids are formed by phase separation, though n ...
will occur, leading to coexisting phases, either completely separated or mixed as a
suspension
Suspension or suspended may refer to:
Science and engineering
* Suspension (topology), in mathematics
* Suspension (dynamical systems), in mathematics
* Suspension of a ring, in mathematics
* Suspension (chemistry), small solid particles suspen ...
. 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
The word schema comes from the Greek word ('), which means ''shape'', or more generally, ''plan''. The plural is ('). In English, both ''schemas'' and ''schemata'' are used as plural forms.
Schema may refer to:
Science and technology
* SCHEMA ...
of
levels on the vertical axis of a
graph
Graph may refer to:
Mathematics
*Graph (discrete mathematics), a structure made of vertices and edges
**Graph theory, the study of such graphs and their properties
*Graph (topology), a topological space resembling a graph in the sense of discre ...
, which can be
high or low
High may refer to:
Science and technology
* Height
* High (atmospheric), a high-pressure area
* High (computability), a quality of a Turing degree, in computability theory
* High (tectonics), in geology an area where relative tectonic uplift t ...
(for example, "high serum levels of bilirubin" are concentrations of
bilirubin
Bilirubin (BR) (Latin for "red bile") is a red-orange compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. This catabolism is a necessary process in the body's clearance of waste products that arise from the ...
in the
blood serum
Serum () is the fluid and solute component of blood which does not play a role in clotting. It may be defined as blood plasma without the clotting factors, or as blood with all cells and clotting factors removed. Serum includes all proteins not ...
that are greater
than normal).
Quantitative notation
There are four quantities that describe concentration:
Mass concentration
The mass concentration
is defined as the
mass
Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different element ...
of a constituent
divided by the volume of the mixture
:
:
The
SI unit
The International System of Units, known by the international abbreviation SI in all languages and sometimes Pleonasm#Acronyms and initialisms, pleonastically as the SI system, is the modern form of the metric system and the world's most wid ...
is kg/m
3 (equal to g/L).
Molar concentration
The molar concentration
is defined as the
amount
Quantity or amount is a property that can exist as a multitude or magnitude, which illustrate discontinuity and continuity. Quantities can be compared in terms of "more", "less", or "equal", or by assigning a numerical value multiple of a uni ...
of a constituent
(in moles) divided by the volume of the mixture
:
:
The SI unit is mol/m
3. However, more commonly the unit mol/L (= mol/dm
3) 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/m
3.
Volume concentration
The volume concentration
(not to be confused with
volume fraction
In chemistry and fluid mechanics, the volume fraction φ''i'' is defined as the volume of a constituent ''V'i'' divided by the volume of all constituents of the mixture ''V'' prior to mixing:
:\phi_i = \frac
Being dimensionless, its unit is ...
) 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. Note that these should not be called concentrations.
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
International Union of Pure and Applied Chemistry
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
and
National Institute of Standards and Technology
The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into Outline of p ...
discourage the use of normality.
Molality
Not to be confused with
molarity
Molar concentration (also called molarity, amount concentration or substance concentration) is a measure of the concentration of a chemical species, in particular of a solute in a solution, in terms of amount of substance per unit volume of solu ...
.
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
In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, th ...
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
Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.
Temperature is a monotonic function of the average molecular kinetic ...
.
Table of concentrations and related quantities
See also
*
*
*
*
References
{{authority control
Analytical chemistry
Chemical properties