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In
chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. T ...

chemistry
, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: ''
mass concentrationMass concentration or mascon may refer to: * Mass concentration (chemistry), the mass of a constituent divided by the volume of a mixture, this formula is generally learned in year 8 * Mass concentration (astronomy), a region of a planet or moon's cr ...
'', ''
molar concentration Molar concentration (also called molarity, amount concentration or substance concentration) is a measure of the concentration In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compoun ...
'', ''
number concentrationThe number density (symbol: ''n'' or ''ρ''N) is an intensive quantity used to describe the degree of concentration In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds ...
'', and ''
volume concentrationIn chemistry, 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 quantity, dimensionless, its unit ...
''. The concentration can refer to any kind of chemical mixture, but most frequently refers to solutes and solvents in
solution Solution may refer to: * Solution (chemistry) Image:SaltInWaterSolutionLiquid.jpg, upMaking a saline water solution by dissolving Salt, table salt (sodium chloride, NaCl) in water. The salt is the solute and the water the solvent. In chemistry ...
s. The molar (amount) concentration has variants such as
normal concentrationIn chemistry, the equivalent concentration or normality of a solution is defined as the molar concentration ''ci'' divided by an equivalence factor ''f''eq: :Normality = Unit symbol N The unit symbol "N" is used to denote "eq/L" (equivalent per ...
and
osmotic concentration Osmotic concentration, formerly known as osmolarity, is the measure of solute upMaking a table salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), sa ...
.


Etymology

The term concentration comes from the word concentrate, from the
French
French
concentrer, from con– + center, meaning “to put at the center”.


Qualitative description

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 upMaking a table salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as a crystallinity, crystalline mineral is known ...
(for example, alcohol), or reduce the amount of
solvent A solvent (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the ...

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
miscible Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration In chemistry Chemistry is the study of the properties and behavior of . It is a that covers ...
, 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 Supersaturation occurs with a chemical solution when the concentration of a solute exceeds the concentration specified by the value equilibrium solubility Solubility is the property of a solid, liquid or gaseous chemical substance called ''s ...
may occur. Instead,
phase separation Phase separation is the creation of two distinct Phase (matter), 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 separati ...

phase separation
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 suspende ...
. 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 discret ...

graph
, which can be
high or low
high or low
(for example, "high serum levels of bilirubin" are concentrations of
bilirubin Bilirubin (BR) is a yellow compound that occurs in the normal catabolic Catabolism () is the set of metabolic pathways that breaks down molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecule ...

bilirubin
in the
blood serum Serum () is the fluid and solute component of blood Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The re ...
that are greater than normal).


Quantitative notation

There are four quantities that describe concentration:


Mass concentration

The mass concentration \rho_i is defined as the
mass Mass is the quantity Quantity 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 ...
of a constituent m_i divided by the volume of the mixture V: :\rho_i = \frac . The
SI unit The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system The metric system is a that succeeded the decimal ...
is kg/m3 (equal to g/L).


Molar concentration

The molar concentration c_i is defined as the
amount Quantity or amount is a property that can exist as a multitude Multitude is a term for a group of people who cannot be classed under any other distinct category, except for their shared fact of existence. The term has a history of use reaching ba ...
of a constituent n_i (in moles) divided by the volume of the mixture V: :c_i = \frac . The
SI unit The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system The metric system is a that succeeded the decimal ...
is mol/m3. However, more commonly the unit mol/L (= mol/dm3) is used.


Number concentration

The number concentration C_i is defined as the number of entities of a constituent N_i in a mixture divided by the volume of the mixture V: :C_i = \frac. The
SI unit The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system The metric system is a that succeeded the decimal ...
is 1/m3.


Volume concentration

The volume concentration \sigma_i (not to be confused with
volume fractionIn chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo ...
) is defined as the volume of a constituent V_i divided by the volume of the mixture V: :\sigma_i = \frac . 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 \sigma_i 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 c_i divided by an equivalence factor f_\mathrm. Since the definition of the equivalence factor depends on context (which reaction is being studied),
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering OrganizationsNational Adhering Organizations in chemistry are the organizations that work as the authoritative power over chemist ...
and
NIST The National Institute of Standards and Technology (NIST) is a physical sciences Physical science is a branch of natural science that studies abiotic component, non-living systems, in contrast to life science. It in turn has many branches, e ...

NIST
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 In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types ...
) The molality of a solution b_i is defined as the
amount Quantity or amount is a property that can exist as a multitude Multitude is a term for a group of people who cannot be classed under any other distinct category, except for their shared fact of existence. The term has a history of use reaching ba ...
of a constituent n_i (in moles) divided by the mass of the solvent m_\mathrm (not the mass of the solution): :b_i = \frac. The
SI unit The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system The metric system is a that succeeded the decimal ...
for molality is mol/kg.


Mole fraction

The mole fraction x_i is defined as the
amount Quantity or amount is a property that can exist as a multitude Multitude is a term for a group of people who cannot be classed under any other distinct category, except for their shared fact of existence. The term has a history of use reaching ba ...
of a constituent n_i (in moles) divided by the total amount of all constituents in a mixture n_\mathrm: :x_i = \frac . The
SI unit The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system The metric system is a that succeeded the decimal ...
is mol/mol. However, the deprecated
parts-per notation In science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of Testability, testable explanations and predictio ...
is often used to describe small mole fractions.


Mole ratio

The mole ratio r_i is defined as the
amount Quantity or amount is a property that can exist as a multitude Multitude is a term for a group of people who cannot be classed under any other distinct category, except for their shared fact of existence. The term has a history of use reaching ba ...
of a constituent n_i divided by the total amount of all ''other'' constituents in a mixture: :r_i = \frac. If n_i is much smaller than n_\mathrm, the mole ratio is almost identical to the mole fraction. The
SI unit The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system The metric system is a that succeeded the decimal ...
is mol/mol. However, the deprecated
parts-per notation In science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of Testability, testable explanations and predictio ...
is often used to describe small mole ratios.


Mass fraction

The mass fraction w_i is the fraction of one substance with mass m_i to the mass of the total mixture m_\mathrm, defined as: :w_i = \frac . The
SI unit The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system The metric system is a that succeeded the decimal ...
is kg/kg. However, the deprecated
parts-per notation In science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of Testability, testable explanations and predictio ...
is often used to describe small mass fractions.


Mass ratio

The mass ratio \zeta_i is defined as the mass of a constituent m_i divided by the total mass of all ''other'' constituents in a mixture: :\zeta_i = \frac. If m_i is much smaller than m_\mathrm, the mass ratio is almost identical to the mass fraction. The
SI unit The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system The metric system is a that succeeded the decimal ...
is kg/kg. However, the deprecated
parts-per notation In science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of Testability, testable explanations and predictio ...
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.


Table of concentrations and related quantities


See also

* * * *


References

{{authority control Analytical chemistry Chemical properties