A carboxylic acid is a compound with one alkyl group and a carboxyl group (one hydroxide group and one carbonyl group, COOH). They usually end with the suffix -oic acid.

Familiar examples are:

  • Methanoic acid, HCOOH, the compound in fire ant stings, which can cause blisters.
  • Ethanoic acid, CH3COOH, the food additive in vinegar. Alcoholic beverages can contain this when the ethanol reacts with oxygen.
  • Citric acid, (COOH)3C3OH or C6H8O7, the sour ingredient in citrus fruits and a food additive and preservative.