A carboxylic acid is an organic compound containing the carboxyl group (–COOH). It matters because it is the parent of a whole family of acid derivatives and because it is a weak acid: it gives up the hydroxyl proton only partially in water. Its acidity is explained by the fact that the resulting conjugate base, the carboxylate ion, is stabilised by resonance delocalisation of the negative charge over both oxygen atoms.

羧酸是含有羧基(–COOH)的有机化合物。它之所以重要,是因为它是一整类酸衍生物的母体,并且是一种弱酸:在水中只部分给出羟基质子。其酸性可由如下事实解释:所生成的共轭碱(羧酸根离子)因负电荷在两个氧原子上的共振离域而被稳定。