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Molar concentrationIn chemistry, '''molar concentration''' (also called '''molarity''', '''amount concentration''' or '''substance concentration''') is a measure of the concentration of a solute in a solution, or of any molecule|molecular, ionic, or atomic Chemical species|species in a given volume. However, in thermodynamics the use of molar concentration is often not very convenient, because the volume of most solutions slightly depends on temperature due to thermal expansion. This problem is usually resolved by introducing temperature correction coefficient|factors, or by using a temperature-independent measure of concentration such as molality.Notation and terminology
Molar concentration is sometimes denoted by ''c'', but more often by simply placing square brackets around the chemical formula or element symbol.Definition
Molar concentration or '''molarity''' ''c'' is defined as amount of substance|amount of solute per unit volume of solution, or per unit volume available to the species:
- .
Here, ''n'' is the amount of the solute,[ ''N'' is the number of molecules present in the volume ''V'', the ratio ''N''/''V'' is the number concentration ''C'', and ''N''A is the Avogadro constant, approximately 6.022 Mole (unit)|mol−1.
]Units
The SI Units of measurement|units for molar concentration are Mole (unit)|mol/Metre|m3. However, most chemical literature traditionally uses Mole (unit)|mol/Decimetre|dm3, which is the same as Mole (unit)|mol/Litre|L. These traditional units are often denoted by a capital letter M (pronounced "molar"), sometimes preceded by an SI prefix, as in:
- Mole (unit)|mol/Metre|m3 = 10-3 Mole (unit)|mol/Decimetre|dm3 = 10-3 Mole (unit)|mol/Litre|L = 10-3 M = 1 mM .
This way, words "millimolar" and "micromolar" refer to mM and μM (10-3 Mole (unit)|mol/Litre|L and 10-6 Mole (unit)|mol/Litre|L) respectively.
Examples
Most proteins are present in the bacteria such as ''E. coli'' at 60 copies or fewer. The volume of a bacterium is 10−15 liter|L, which gives us ''c'' = ''N''/ = 10−7 M = 100 nM. (Here, nM is "nanomolar", ''i.e.'' 10-9 moles per liter).
Consider 2 grams of Sodium chloride|NaCl dissolved in 15 milliliter|mL of water. As 58 grams of NaCl is 1 mole of formula units (since the molar mass of NaCl is 58 g/mol), and 1 milliliter is 0.001 liter, this gives ''c'' = (2/58 Mole (unit)|mol)/(0.015 L) = 2.3 M.
See also
- Molar solution
- Concentration#Normality|Normality
- Osmolarity
- Molecular weight
References
External links
- Experiment to determine the molar concentration of vinegar by titration
- Concentration Calculator and Concentration Converter
Category:Amount of substance
Category:Analytical chemistry
Category:Solutions
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