Will sodium benzoate be more soluble in water than benzoic acid
The Correct Answer and Explanation is:
Correct Answer: Yes, sodium benzoate is more soluble in water than benzoic acid.
Explanation
The solubility of a compound in water is largely influenced by its polarity and ability to form hydrogen bonds or ionic interactions with water molecules. Sodium benzoate and benzoic acid are related compounds, but their structural differences significantly affect their solubility.
Benzoic acid (C₆H₅COOH) is a weak organic acid consisting of a benzene ring attached to a carboxylic acid group. While it can form some hydrogen bonds with water, its large non-polar benzene ring limits overall polarity, reducing its water solubility. In aqueous solution, only a small portion of benzoic acid ionizes to form benzoate ions and hydrogen ions, especially in acidic conditions. The unionized form of benzoic acid is only sparingly soluble in water, with solubility around 0.34 g per 100 mL at room temperature.
In contrast, sodium benzoate (C₆H₅COONa) is the sodium salt of benzoic acid. It consists of a benzoate anion and a sodium cation. Salts like sodium benzoate dissociate fully in water into ions, which are highly polar and interact strongly with the polar water molecules through ion-dipole interactions. This makes sodium benzoate significantly more soluble in water, with solubility exceeding 60 g per 100 mL at room temperature.
Additionally, pH plays an important role. In neutral to basic conditions, benzoic acid is deprotonated to form benzoate, which increases solubility. But sodium benzoate is already in the ionized form, making it readily soluble even without pH adjustments.
In summary, sodium benzoate is much more water-soluble than benzoic acid due to its ionic nature and the ability of its dissociated ions to interact favorably with water. This property makes sodium benzoate a common preservative in food and pharmaceutical products where high aqueous solubility is essential.
