SQA Higher Chemistry Practice Exam

A carboxylic acid is specifically defined by the presence of the carboxyl functional group, which has the structure ─COOH. This functional group includes both a carbonyl group (C=O) and a hydroxyl group (−OH) attached to the same carbon atom. The unique properties and reactivity of carboxylic acids arise from this specific structure.

For example, the presence of the acidic hydrogen in the hydroxyl part of the carboxyl group allows carboxylic acids to donate that hydrogen ion (H⁺) in solution, giving them their acidic characteristics. This also allows them to participate in various chemical reactions, such as esterification, where they can react with alcohols to form esters.

In contrast, the other options describe different functional groups that do not define a carboxylic acid. A molecule containing a hydroxyl group does not necessarily have a carboxyl group and could refer to alcohols. A molecule with a ketone functional group contains a carbonyl group (C=O) but lacks the hydroxyl part of the ─COOH structure. A molecule with a methyl group indicates a simple carbon group (−CH₃) and does not imply the