A common way to make carboxylic acid that is insoluble in water soluble in water is to add a base to create the carboxylate salt and water, add an acid to lower the pH of the solution, add more water and stir vigorously, or use a different carboxylic acid.
The Correct Answer and Explanation is:
Correct answer: Add a base to create the carboxylate salt and water.
Explanation:
Carboxylic acids are organic compounds that contain the –COOH functional group. While some small carboxylic acids such as formic acid or acetic acid are soluble in water, larger or more hydrophobic ones tend to be poorly soluble. This limited solubility can be overcome by converting the carboxylic acid into its salt form, which is more polar and therefore more compatible with water.
When a base is added to a carboxylic acid, a neutralization reaction occurs. The acidic proton (H⁺) from the –COOH group is removed by the base, forming water and a carboxylate anion (–COO⁻). This anion pairs with the cation from the base (often sodium or potassium), forming a carboxylate salt such as sodium acetate. The carboxylate salt is much more soluble in water due to its ionic nature. Ionic compounds tend to interact strongly with water molecules through ion-dipole interactions, which promote solubility.
For example, benzoic acid is only slightly soluble in cold water. However, when sodium hydroxide (a strong base) is added, it reacts with benzoic acid to form sodium benzoate and water. Sodium benzoate, being a salt, dissolves readily in water.
Adding an acid to lower the pH would reverse this reaction by reprotonating the carboxylate ion, regenerating the carboxylic acid and causing it to precipitate. Adding more water and stirring may not be effective if the compound is inherently hydrophobic. Using a different carboxylic acid would only help if it naturally has better solubility, which does not directly address the solubility of the original compound.
Thus, the most effective and common method to make a water-insoluble carboxylic acid soluble in water is to add a base and form the water-soluble carboxylate salt.
