Editing Carboxylic acid (section)

===Acidity===
Carboxylic acids are [[Brønsted–Lowry acid–base theory|Brønsted–Lowry acids]] because they are proton (H<sup>+</sup>) donors. They are the most common type of [[organic acid]].{{cn|date=May 2025}}

Carboxylic acids are typically [[weak acid]]s, meaning that they only partially [[Dissociation (chemistry)|dissociate]] into [[Hydronium|{{chem2|[H3O]+}}]] [[cation]]s and [[Carboxylate|{{chem2|R\sCO2−}}]] [[anion]]s in neutral [[Water (molecule)|aqueous]] solution. For example, at room temperature, in a 1-[[molarity|molar]] solution of [[acetic acid]], only 0.001% of the acid are dissociated (i.e. 10<sup>−5</sup> moles out of 1&nbsp;mol). Electron-withdrawing substituents such as [[Trifluoromethyl group|trifluoromethyl]] ({{chem2|\sCF3}}) give stronger acids (the p''K''<sub>a</sub> of acetic acid is 4.76 whereas trifluoroacetic acid, with a [[Trifluoromethyl group|trifluoromethyl substituent]], has a p''K''<sub>a</sub> of 0.23). Electron-donating substituents give weaker acids (the p''K''<sub>a</sub> of formic acid is 3.75 whereas acetic acid, with a [[Methyl group|methyl substituent]], has a p''K''<sub>a</sub> of 4.76){{cn|date=May 2025}}
{|class = "wikitable"
! Carboxylic acid<ref>{{cite book | editor-last= Haynes |editor-first=William M. | year = 2011 | title = CRC Handbook of Chemistry and Physics | edition = 92nd | publisher = [[CRC Press]] | isbn = 978-1439855119|pages=5–94 to 5–98|title-link=CRC Handbook of Chemistry and Physics}}</ref>
! [[Acid dissociation constant|p''K''<sub>a</sub>]]
|-
|[[Formic acid]] ({{chem2|HCO2H}}) || 3.75
|-
|[[Chloroformic acid]] ({{chem2|ClCO2H}}) || 0.27<ref name=metabolites>{{cite web | url = https://hmdb.ca/metabolites/HMDB0250109 | title = Chlorocarbonic acid | work =  Human Metabolome Database }}</ref>
|-
|[[Acetic acid]] ({{chem2|CH3CO2H}})|| 4.76
|-
|[[Glycine]] ({{chem2|NH2CH2CO2H}})||2.34
|-
|[[Fluoroacetic acid]] ({{chem2|FCH2CO2H}}) || 2.586
|-
|[[Difluoroacetic acid]] ({{chem2|F2CHCO2H}})|| 1.33
|-
|[[Trifluoroacetic acid]] ({{chem2|CF3CO2H}})|| 0.23
|-
|[[Chloroacetic acid]] ({{chem2|ClCH2CO2H}})|| 2.86
|-
|[[Dichloroacetic acid]] ({{chem2|Cl2CHCO2H}})|| 1.29
|-
|[[Trichloroacetic acid]] ({{chem2|CCl3CO2H}})|| 0.65
|-
|[[Benzoic acid]] ({{chem2|C6H5\sCO2H}})||4.2
|-
|[[2-Nitrobenzoic acid]] (''ortho''-{{chem2|C6H4(NO2)CO2H}})||2.16
|-
|[[Oxalic acid]] ({{chem2|HO\sC(\dO)\sC(\dO)\sOH}}) (first dissociation)
| 1.27
|-
|[[Oxalic acid#Acid-base properties|Hydrogen oxalate]] ({{chem2|HO\sC(\dO)\sCO2−}}) (second dissociation of oxalic acid)
|4.14
|-
|}
[[Deprotonation]] of carboxylic acids gives carboxylate anions; these are [[resonance stabilized]], because the negative charge is delocalized over the two oxygen atoms, increasing the stability of the anion. Each of the carbon–oxygen bonds in the carboxylate anion has a partial double-bond character. The carbonyl carbon's partial positive charge is also weakened by the −<sup>1</sup>/<sub>2</sub> negative charges on the 2 oxygen atoms.{{cn|date=May 2025}}