Concentration

Concentration

Overview
In chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

, 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. The term concentration can be applied to any kind of chemical mixture, but most frequently it refers to solute
Solute
Solute may refer to:* Solute, UMIK or UBOOK desolving in a substance,forming INT/INTY* Solute , a group of Paleozoic echinoderms...

s in homogeneous solution
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...

s.

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.
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Encyclopedia
In chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

, 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. The term concentration can be applied to any kind of chemical mixture, but most frequently it refers to solute
Solute
Solute may refer to:* Solute, UMIK or UBOOK desolving in a substance,forming INT/INTY* Solute , a group of Paleozoic echinoderms...

s in homogeneous solution
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...

s.

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
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...

 (for example, alcohol), or reduce the amount of solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...

 (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
Saturation (chemistry)
In chemistry, saturation has six different meanings, all based on reaching a maximum capacity...

. If additional solute is added to a saturated solution, it will not dissolve (except in certain circumstances, when supersaturation
Supersaturation
The term supersaturation refers to a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances...

 may occur). Instead, phase separation will occur, leading to coexisting phases (either completely separated or mixed as a suspension
Suspension (chemistry)
In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometer. The internal phase is dispersed throughout the external phase through mechanical agitation, with the use of certain...

. The point of saturation depends on many variables such as ambient temperature and the precise chemical nature of the solvent and solute.

Mass concentration


The mass concentration is defined as the mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

 of a constituent divided by the volume of the mixture :


The SI-unit
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

 is kg/m3.

Molar concentration


The molar concentration is defined as the amount
Amount of substance
Amount of substance is a standards-defined quantity that measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons, and other particles. It is sometimes referred to as chemical amount. The International System of Units defines the amount of substance to be...

 of a constituent divided by the volume of the mixture :


The SI-unit
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

 is mol/m3. However, more commonly the unit mol/L 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
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

 is 1/m3.

Volume concentration


The volume concentration (also called volume fraction) is defined as the volume of a constituent divided by the volume of all consituents of the mixture prior to mixing:


The SI-unit
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

 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


Normality is defined as the molar concentration divided by an equivalence factor . Since the definition of the equivalence factor may not be unequivocal, IUPAC and NIST discourage the use of normality.

Molality


The molality of a solution is defined as the amount
Amount of substance
Amount of substance is a standards-defined quantity that measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons, and other particles. It is sometimes referred to as chemical amount. The International System of Units defines the amount of substance to be...

 of a constituent divided by the mass of the solvent (not the mass of the solution):


The SI-unit
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

 for molality is mol/kg.

Mole fraction


The mole fraction is defined as the amount
Amount of substance
Amount of substance is a standards-defined quantity that measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons, and other particles. It is sometimes referred to as chemical amount. The International System of Units defines the amount of substance to be...

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


The SI-unit
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

 is mol/mol. However, the deprecated parts-per notation
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, they are pure numbers with no associated units of measurement...

 is often used to describe small mole fractions.

Mole ratio


The mole ratio is defined as the amount
Amount of substance
Amount of substance is a standards-defined quantity that measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons, and other particles. It is sometimes referred to as chemical amount. The International System of Units defines the amount of substance to be...

 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
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

 is mol/mol. However, the deprecated parts-per notation
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, they are pure numbers with no associated units of measurement...

 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
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

 is kg/kg. However, the deprecated parts-per notation
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, they are pure numbers with no associated units of measurement...

 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
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

 is kg/kg. However, the deprecated parts-per notation
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, they are pure numbers with no associated units of measurement...

 is often used to describe small mass ratios.

Dependence on volume


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

Table of concentrations and related quantities

Concentration type Symbol Definition SI-unit other unit(s)
mass concentration or kg/m3 g/100mL (=g/dL)
molar concentration mol/m3 M (=mol/L)
number concentration 1/m3 1/cm3
volume concentration m3/m3
Related quantities Symbol Definition SI-unit other unit(s)
normality mol/m3 M (=mol/L)
molality mol/kg
mole fraction mol/mol ppm, ppb, ppt
mole ratio mol/mol ppm, ppb, ppt
mass fraction kg/kg ppm, ppb, ppt
mass ratio kg/kg ppm, ppb, ppt

See also

  • Serial dilution
    Serial dilution
    A serial dilution is the stepwise dilution of a substance in solution. Usually the dilution factor at each step is constant, resulting in a geometric progression of the concentration in a logarithmic fashion. A ten-fold serial dilution could be 1 M, 0.1 M, 0.01 M, 0.001 M.....

  • Practical examples of 1 and 2 normal acids in biochemistry