NCEA Level 2 Organic Chemistry 2025 – 400 Free Practice Questions to Pass the Exam

The compound that is considered a carboxylic acid is CH3COOH, commonly known as acetic acid. This classification stems from its functional group, which is characterized by the presence of the carboxyl group (-COOH). The carboxyl group is composed of a carbon atom that is double bonded to an oxygen atom (carbonyl) and also single bonded to a hydroxyl group (-OH). This unique structure gives carboxylic acids their distinctive properties, such as being able to donate a proton (H+) in an aqueous solution, thus exhibiting acidic behavior.

The other compounds do not possess the carboxyl functional group. CH3OH is methanol, an alcohol, which contains a hydroxyl group (-OH) attached to a carbon atom but lacks the carbonyl part vital for carboxylic acids. CH3CH2NH2 is ethylamine, an amine with a nitrogen atom instead of a carboxyl group, and CH4 is methane, which is a simple hydrocarbon without any functional groups related to acids. Thus, CH3COOH is the only compound among the options given that fits the definition of a carboxylic acid.