Identify the following compounds as Acid, Base or Neutral. a. Benzocaine: (2 points) b. Biphenyl: (2 points) c. Trans-cinnamic acid: (2 points)
The Correct Answer and Explanation is :
a. Benzocaine: Base
Benzocaine is a weak base. It is an ester of the amino acid para-aminobenzoic acid, with an amine group in its structure. The presence of the amine group (–NH2) contributes basic properties, as amines tend to accept protons (H+) in a solution. The nitrogen atom in the amine group has a lone pair of electrons, allowing it to accept a proton, hence acting as a base. The ester group does not significantly alter this basicity. However, since benzocaine is a weak base, its ability to accept protons is limited, making it a weak base in aqueous solutions.
b. Biphenyl: Neutral
Biphenyl is a neutral compound. It consists of two benzene rings connected by a single bond, and its structure does not contain any functional groups that would impart acidic or basic properties. Benzene rings are relatively non-polar and do not have groups that would either donate or accept protons in a typical acid-base reaction. As a result, biphenyl does not exhibit acidic or basic behavior in water and is classified as neutral.
c. Trans-cinnamic acid: Acid
Trans-cinnamic acid is an organic acid. The carboxyl group (–COOH) in cinnamic acid is the defining feature of its acidic behavior. The carboxyl group can donate a proton (H+) due to the presence of the electron-withdrawing carbonyl group (C=O) adjacent to the hydroxyl group (–OH), making it a weak acid. In water, cinnamic acid dissociates partially, releasing H+ ions and acting as an acid. Its acidity is moderate compared to strong acids like HCl, but it is definitely more acidic than a neutral compound like biphenyl or a base like benzocaine.
Summary:
- Benzocaine is a weak base due to the presence of an amine group.
- Biphenyl is neutral because it lacks functional groups that would donate or accept protons.
- Trans-cinnamic acid is an acid because it contains a carboxyl group that can donate a proton.