Semmelweis Chemistry Entrance Practice Exam

Acetic acid is characterized by the presence of a carboxyl group, which is a functional group characterized by a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group (–COOH). This particular arrangement of atoms gives acetic acid its acidic properties, as the hydrogen atom from the hydroxyl group can dissociate in solution, releasing hydrogen ions (H⁺) and leading to the acid's characteristic behavior.

The carboxyl group is essential for the properties of acetic acid, influencing its reactivity and interactions with other molecules. For instance, the presence of this group allows acetic acid to participate in reactions typical of acids, such as esterification, where it can react with alcohols to form esters.

The other functional groups listed do not represent the structure or properties of acetic acid. Aldehydes contain a carbonyl group bonded to at least one hydrogen, alcohols have a hydroxyl group bonded to a carbon, and amines feature nitrogen atoms bonded to carbon atoms. Thus, while all of these groups are important in organic chemistry, it is the carboxyl group that is definitive for acetic acid and explains both its structure and acidic nature.