Editing Molar concentration (section)

==Definition==
Molar concentration or molarity is most commonly expressed in units of moles of [[solute]] per litre of [[Solution (chemistry)|solution]].<ref>{{Cite book|title=Introductory chemistry essentials|last=Tro, Nivaldo J.|date=6 January 2014|isbn=9780321919052|edition= Fifth|location=Boston|pages=457|oclc=857356651}}</ref> For use in broader applications, it is defined as [[amount of substance]] of solute per unit volume of solution, or per unit volume available to the species, represented by lowercase <math>c</math>:<ref name="GoldBook">{{GoldBookRef|title=amount concentration, ''c''|file=A00295}}</ref>

:<math>c = \frac{n}{V} = \frac{N}{N_\text{A}\,V} = \frac{C}{N_\text{A}}.</math>

Here, <math>n</math> is the amount of the solute in moles,<ref name=kaufman/> <math>N</math> is the number of [[particle number|constituent particle]]s present in volume <math>V</math> (in litres) of the solution, and <math>N_\text{A}</math> is the [[Avogadro constant]], since 2019 defined as exactly {{physconst|NA|ref=no}}. The ratio <math>\frac{N}{V}</math> is the [[number density]] <math>C</math>.

In [[thermodynamics]], the use of molar concentration is often not 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]].<ref name=kaufman>{{Cite book| author = Kaufman, Myron| title = Principles of thermodynamics| page = 213| publisher = CRC Press| year = 2002| isbn = 0-8247-0692-7}}</ref>

The [[wikt: reciprocal|reciprocal]] quantity represents the dilution (volume) which can appear in Ostwald's [[law of dilution]].

===Formality or analytical concentration===
{{anchor|Formal}}<!--[[Formal concentration]] redirects here --><!--[[Analytical concentration]] redirects here -->
If a molecule or salt dissociates in solution, the concentration refers to the original chemical formula in solution, the molar concentration is sometimes called '''formal concentration''' or '''formality''' (''F''<sub>A</sub>) or '''analytical concentration''' (''c''<sub>A</sub>). For example, if a sodium carbonate solution ({{chem2|Na2CO3}}) has a formal concentration of ''c''({{chem2|Na2CO3}}) = 1&nbsp;mol/L, the molar concentrations are ''c''({{chem2|Na+}}) = 2&nbsp;mol/L and ''c''({{chem2|CO3(2−)}}) = 1&nbsp;mol/L because the salt dissociates into these ions.<ref name="Harvey_2020">{{Cite web |title=2.2: Concentration |last=Harvey |first=David |work=Chemistry LibreTexts |date=2020-06-15 |access-date=2021-12-15 |url= https://chem.libretexts.org/Courses/BethuneCookman_University/B-CU%3A_CH-345_Quantitative_Analysis/Book%3A_Analytical_Chemistry_2.1_(Harvey)/02%3A_Basic_Tools_of_Analytical_Chemistry/2.02%3A_Concentration}}</ref>