Question Video: Recognizing Carboxylic Acid Esterification from the Reagents, Conditions, and Results of a Chemical Test Chemistry

An unknown liquid is combined with ethanol and a few drops of sulfuric acid. The mixture is heated with a Bunsen burner flame. The resulting reaction produces a compound that smells like pineapples. What is the formula of the unknown liquid? [A] RCH₃ [B] RCH₂OH [C] RCOOH [D] RCHO [E] RCOCH₃

02:53

Video Transcript

An unknown liquid is combined with ethanol and a few drops of sulfuric acid. The mixture is heated with a Bunsen burner flame. The resulting reaction produces a compound that smells like pineapples. What is the formula of the unknown liquid? (A) RCH3, (B) RCH2OH, (C) RCOOH, (D) RCHO, or (E) RCOCH3.

The question is describing a particular experiment. In this experiment, an unknown liquid is combined with ethanol, an alcohol, and a few drops of sulfuric acid. The mixture is then heated to produce a compound that has a pineapple-like scent. We need to use this information to determine the formula of the unknown liquid. Let’s start by considering the product. There are many organic compounds that have characteristic scents, but one class of organic compounds typically has a fruity or floral scent. This class of organic compounds is known as esters.

The experimental setup described is known as the ester test. The ester test is performed to determine if an organic sample contains a carboxylic acid. A carboxylic acid is a molecule which contains a carboxyl group. When a carboxylic acid is reacted with an alcohol in the presence of an acid catalyst and heat, as is the case during an ester test, the hydroxy group of the carboxylic acid is replaced by the alkoxy portion of the alcohol. This produces an ester — which typically smells sweet, fruity, or floral — and water. As the ester test described in the question produced a fruity smelling compound when a substance was reacted with an alcohol in the presence of an acid catalyst and heat, we can conclude that the unknown liquid is a carboxylic acid.

Looking at the generic structure of a carboxylic acid given in the reaction equation, we can determine that the formula of a generic carboxylic acid must contain an R group, one carbon atom, two oxygen atoms, and one hydrogen atom. This matches the formula shown in answer choice (C). Thus, an unknown liquid that produces a compound that smells like pineapples upon being heated with ethanol and a few drops of sulfuric acid has a formula of RCOOH, or answer choice (C).

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.