Suppose you have a sample of benzoic acid dissolved in water.
b. Now assume that aqueous NaOH is added to the benzoic acid solution until pH 12 is reached. Draw the structure of the major organic species present.

Verified step by step guidance

1. Identify the chemical structure of benzoic acid. Benzoic acid is an aromatic carboxylic acid with the formula C₆H₅COOH. The carboxylic acid group (-COOH) is the functional group responsible for its acidic properties.
2. Understand the reaction between benzoic acid and NaOH. Benzoic acid reacts with a strong base like NaOH in a neutralization reaction. The hydroxide ion (OH⁻) from NaOH deprotonates the carboxylic acid group (-COOH), forming water (H₂O) and the conjugate base of benzoic acid, which is the benzoate ion (C₆H₅COO⁻).
3. Recognize the effect of pH 12. At pH 12, the solution is strongly basic, meaning that essentially all of the benzoic acid will have been converted to its conjugate base, the benzoate ion (C₆H₅COO⁻). This is because the pKa of benzoic acid is approximately 4.2, and at pH 12, the environment is far above the pKa, favoring the deprotonated form.
4. Draw the structure of the major organic species. The major organic species present at pH 12 is the benzoate ion. Its structure consists of a benzene ring (C₆H₅) attached to a carboxylate group (-COO⁻), where the hydrogen atom from the carboxylic acid group has been removed.
5. Summarize the reaction and the resulting species. The reaction can be summarized as: C₆H₅COOH + OH⁻ → C₆H₅COO⁻ + H₂O. The major organic species present at pH 12 is the benzoate ion (C₆H₅COO⁻).

Key Concepts

Benzoic Acid

Benzoic acid is a simple aromatic carboxylic acid with the formula C6H5COOH. It is characterized by a benzene ring attached to a carboxyl group (-COOH). In aqueous solutions, benzoic acid can partially dissociate to form benzoate ions (C6H5COO-) and hydrogen ions (H+), depending on the pH of the solution.

pH and Acid-Base Reactions

pH is a measure of the acidity or basicity of a solution, with lower values indicating higher acidity. When NaOH, a strong base, is added to benzoic acid, it reacts to neutralize the acid, forming water and benzoate ions. At pH 12, the solution is highly basic, leading to the complete deprotonation of benzoic acid, resulting in the predominant presence of benzoate ions.

Organic Species in Aqueous Solutions

In aqueous solutions, the major organic species present depend on the pH and the nature of the solute. At pH 12, benzoic acid is fully deprotonated, and the major species is the benzoate ion (C6H5COO-). Understanding the structure of these species is crucial for predicting their behavior in chemical reactions and their interactions in biological systems.