Carboxylic acids are Brønsted–Lowry acids because they are proton (H) donors. They are the most common type of organic acid.
Carboxylic acids are typically weak acids, meaning that they only partially dissociate into Hydronium| cations and Carboxylate| anions in neutral aqueous solution. For example, at room temperature, in a 1-molar solution of acetic acid, only 0.001% of the acid are dissociated (i.e. 10 moles out of 1 mol). Electron-withdrawing substituents, such as -CF group, give stronger acids (the pK of acetic acid is 4.76 whereas trifluoroacetic acid, with a trifluoromethyl substituent, has a pK of 0.23). Electron-donating substituents give weaker acids (the pK of formic acid is 3.75 whereas acetic acid, with a methyl substituent, has a pK of 4.76)
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 -/ negative charges on the 2 oxygen atoms.