Phenylephrine, an organic substance with molecular formula C9H13NO2, is used as a nasal decongenstant in over-thecounter medications. The molecular structure of phenylephrine is shown below using the usual shortcut organic structure. (a) Would you expect a solution of phenylephrine to be acidic, neutral, or basic?

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Identify the functional groups present in the molecular structure of phenylephrine. Look for groups that can donate or accept protons (H+).

Notice the presence of an amine group (NH2) in the structure. Amines are known to be basic because they can accept a proton.

Consider the presence of any other functional groups that might influence the acidity or basicity of the molecule. In this case, the structure does not contain any strongly acidic groups like carboxylic acids.

Evaluate the overall structure to determine if there are any other factors that might affect the pH of the solution. The presence of the aromatic ring does not significantly affect the basicity of the amine group.

Conclude that the solution of phenylephrine is expected to be basic due to the presence of the amine group, which can accept protons and increase the pH of the solution.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Acid-Base Chemistry

Acid-base chemistry involves the study of substances that can donate protons (acids) or accept protons (bases). The pH scale measures the acidity or basicity of a solution, with values below 7 indicating acidity, 7 being neutral, and above 7 indicating basicity. Understanding the nature of a compound's functional groups is crucial in predicting its behavior in solution.

Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. In phenylephrine, the presence of an amine group (-NH2) and a hydroxyl group (-OH) suggests potential for both basic and acidic behavior, influencing the overall acidity or basicity of the compound in solution.

Ionization of Phenylephrine

The ionization of phenylephrine in solution is determined by its ability to donate or accept protons. The amine group can accept protons, making the compound more basic, while the hydroxyl group can donate protons, contributing to acidity. The balance between these interactions will dictate whether the solution is acidic, neutral, or basic.

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Textbook Question

The following diagrams represent aqueous solutions of three acids, HX, HY, and HZ. The water molecules have been omitted for clarity, and the hydrated proton is represented as H+ rather than H3O+.(b) Which acid would have the smallest aciddissociation constant, Ka?

Textbook Question

Each of the three molecules shown here contains an OH group, but one molecule acts as a base, one as an acid, and the third is neither acid nor base. (c) Which one is neither acidic nor basic?

Textbook Question

Phenylephrine, an organic substance with molecular formula C9H13NO2, is used as a nasal decongenstant in over-thecounter medications. The molecular structure of phenylephrine is shown below using the usual shortcut organic structure. (c) Would you expect a solution of phenylephrine hydrochloride to be acidic, neutral, or basic?

Textbook Question

Consider the molecular models shown here, where X represents a halogen atom. (a) If X is the same atom in both molecules, which molecule will be more acidic?

Textbook Question

Consider the molecular models shown here, where X represents a halogen atom. (b) Does the acidity of each molecule increase or decrease as the electronegativity of the atom X increases?