The solubility of benzoic acid in water is 3.4 grams per liter (g/L). This indicates that at a standard temperature, approximately 3.4 grams of benzoic acid can dissolve in one liter of water to form a saturated solution.
Understanding Benzoic Acid and its Solubility
Benzoic acid is a simple aromatic carboxylic acid, widely known for its various applications, particularly as a food preservative. Its solubility in water is a crucial property that affects its use in different chemical and industrial processes. Solubility refers to the maximum amount of a substance (solute) that can dissolve in a given amount of solvent at a specific temperature. For benzoic acid, its relatively low solubility in water compared to its significant solubility in organic solvents is a characteristic trait.Key Properties of Benzoic Acid
To provide a clearer picture, here are some essential properties of benzoic acid:| Property | Value |
|---|---|
| CAS Reg. No. | 65-85-0 |
| Molar mass | 122.12 g/mol |
| Appearance | White crystals |
| Melting point | 122 ºC |
| Water solubility | 3.4 g/L |
Factors Influencing Benzoic Acid Solubility
While the stated solubility of 3.4 g/L refers to its solubility in pure water at typical room temperature, several factors can significantly influence how much benzoic acid dissolves.Temperature
The solubility of benzoic acid, like most solids, increases with rising temperature. For instance, while it is sparingly soluble in cold water, its solubility dramatically improves in hot water. This property is often utilized in its purification through recrystallization, where it is dissolved in hot water and then allowed to cool, causing pure benzoic acid crystals to precipitate out.pH
The most significant factor affecting benzoic acid's solubility in water is the pH of the solution. Benzoic acid is a weak acid, meaning it partially dissociates in water into a benzoate ion and a proton.- Acidic Conditions (Low pH): In acidic solutions (low pH), the equilibrium shifts towards the undissociated benzoic acid molecule. Since the undissociated form is less polar, its solubility in water is lower.
- Alkaline Conditions (High pH): In alkaline (basic) solutions (high pH), the benzoic acid readily deprotonates to form the benzoate ion (C₆H₅COO⁻). The benzoate ion is charged and much more polar than the neutral benzoic acid molecule, making it highly soluble in water. This is why benzoic acid and its salts (like sodium benzoate) are often used as preservatives, as they become much more soluble and effective at higher pH values.
Practical Applications and Considerations
Understanding the solubility of benzoic acid is critical for its various applications. For example:- Food Preservation: Benzoic acid and its salts are widely used as food preservatives (E210, E211, E212, E213) to inhibit the growth of mold, yeast, and some bacteria. Their effectiveness is highly dependent on the pH of the food product, as they are most active in their undissociated, less soluble form at acidic pH levels (typically below pH 4.5).
- Chemical Synthesis: In organic chemistry, its solubility properties dictate solvent choices for reactions involving benzoic acid, ensuring efficient mixing and reaction kinetics.
- Pharmaceutical Formulations: When incorporated into pharmaceutical products, the solubility characteristics influence formulation design, bioavailability, and drug delivery.
