Benzoic acid Properties Melting point: 121-125 °C (lit) Boiling point: 249 °C (lit) Density: 4.21 (vs air) Vapor density: 10 mm Hg at 132 °C Vapor pressure: 2131 Refractive index Flash point: 250 °F Storage temp: Store at RT Solubility: soluble; clear; colorless (95% ethanol, 1g/3mL) Solid solubility: 4.19 (at 25°C) Pka: 2.5-3.5 (H2O, 20°C saturated solution) Form: White to yellow-beige to orange Color: Slightly soluble Water solubility: 0.34 g/100 mL JECFA Number: 850 Merck BRN: 636131 Henrys Law Constant: 7.02 x 10^-8 atm·m^3/mol Stability: Stable CAS DataBase Reference: 85-09-0 NIST Chambala Rule: 1091
The Correct Answer and Explanation is:
The properties of Benzoic Acid are summarized below, along with an explanation:
Key Properties:
- Melting Point: 121 to 125 °C (literature value)
- Boiling Point: 249 °C (literature value)
- Density (compared to air): 4.21
- Vapor Density: 10 mm Hg at 132 °C
- Vapor Pressure: 2131 (units not specified, likely in Pascal or mm Hg at given conditions)
- Refractive Index: Not provided explicitly
- Flash Point: 250 °F
- Storage Temperature: Store at room temperature
- Ethanol Solubility: Soluble; forms a clear, colorless solution with 95 percent ethanol at 1g per 3mL
- Solid Solubility: 4.19 at 25 °C (likely grams per 100mL in a specified solvent)
- pKa: Between 2.5 to 3.5 in water at 20 °C using a saturated solution
- Physical Form: White to yellow-beige to orange solid
- Color: Slightly soluble in water
- Water Solubility: 0.34 grams per 100mL
- JECFA Number: 850
- Merck BRN: 636131
- Henry’s Law Constant: 7.02 x 10⁻⁸ atm·m³/mol
- Stability: Stable under normal conditions
- CAS Number: 85-09-0
- NIST Reference (Chambala Rule): 1091
Explanation:
Benzoic acid is a widely used organic compound and serves as a fundamental carboxylic acid in both laboratory and industrial applications. Its relatively low melting point of 121 to 125 °C allows it to be easily purified by recrystallization. The boiling point of 249 °C indicates its thermal stability, making it suitable for moderate heating without decomposition.
The compound is only slightly soluble in water (0.34 g/100 mL), but much more soluble in organic solvents like ethanol. This property is important for extraction and purification processes. Its pKa between 2.5 to 3.5 reflects its weak acidic nature, common for carboxylic acids, allowing it to participate in acid-base reactions.
The vapor density and vapor pressure indicate moderate volatility under heating. The flash point of 250 °F highlights the temperature at which vapors can ignite, informing safety protocols.
It exists in solid form, ranging from white to beige or orange, depending on purity or storage conditions. The Henry’s Law constant suggests very low volatility from aqueous solutions, which is beneficial in environmental contexts as it limits air contamination.
Overall, benzoic acid’s stability, moderate acidity, and solubility profile make it valuable in food preservation, pharmaceuticals, and as an intermediate in organic synthesis.
