How to distinguish between benzene and benzoic acid

Benzene and benzoic acid are two substances that are often confused in chemical properties and applications, and they have important applications in many fields, especially in the chemical industry. There are significant differences in structure, properties and reaction characteristics between the two, and the correct distinction between them is essential for production, safety and environmental protection. This paper will analyze how to distinguish benzene and benzoic acid from four aspects: structural analysis, physical properties, chemical properties and identification methods.

1. Structure Analysis: Differences in Molecular Structure between Benzene and Benzoic Acid

1. structural characteristics of benzene

• benzene is a colorless, odorless liquid, molecular structure by 6 carbon atoms through covalent bonds to form a plane regular hexagonal structure, interspersed with a π bond. Its molecular formula is C6H6.
• At room temperature, benzene is a liquid with a boiling point of 80.1°C and a density of 0.8765g/cm³.
• Benzene has a unique aromatic odor and is used as a solvent and synthetic raw material in many organic compounds.

1. Structural characteristics of benzoic acid

• benzoic acid is a white solid with a molecular structure consisting of a benzene ring connected to a carboxylic acid group (-COOH), and the molecular formula is C6H5COOH. In its structure, the benzene rings are linked by a carboxylic acid group (-COOH).
• The crystals of benzoic acid show different colors and shapes at different temperatures, and are white or almost white solids at room temperature.

1. structure contrast

• the molecular structure of benzene and benzoic acid both contain benzene rings, but benzoic acid is attached to an additional carboxylic acid group on the benzene ring, making it significantly different in molecular weight and physical properties.
• Benzoic acid has a larger molecular weight and a higher melting point and boiling point than benzene.

2. Physical Properties: Identification of Benzene and Benzoic Acid

1. density and state

• benzene is a colorless liquid at room temperature with a density of about 0.8765g/cm³.
• Benzoic acid is a white or off-white solid at room temperature with a density of 1.046g/cm³.

1. Solubility and Volatility

• benzene is easily soluble in organic solvents and has strong volatility.
• Benzoic acid is slightly soluble in water and easily soluble in organic solvents at room temperature, but its volatility is poor.

1. melting point and boiling point

• benzene has a melting point of 5.5°C and a boiling point of 80.1°C.
• Benzoic acid has a melting point of 50°C and a boiling point of 233°C.

1. Color and smell

• benzene is colorless and has no obvious odor.
• Benzoic acid is a white solid at room temperature, with a pungent sour taste.

3. chemistry: Reaction characteristics of benzene with benzoic acid

1. acidic reaction

• benzene itself is not acidic, but the hydroxyl group on its ring can be oxidized to form benzoic acid under specific conditions.
• Benzoic acid itself is acidic and can be neutralized with alkaline substances.

1. redox reaction

• benzene can be oxidized under acidic conditions to produce benzoic acid.
• Benzoic acid can be further oxidized under acidic conditions to form higher carbon chain phenol derivatives.

1. reactivity

• benzene has a stronger ring activation effect and can react with anhydrides and other substances.
• The carboxylic acid group of benzoic acid makes it more active in the reaction and can react with basic substances.

4. Identification Method: How to Quickly Distinguish Benzene from Benzoic Acid

1. physical identification method

• density test: Density test using graduated cylinder and water. Pour the two substances into the cylinder separately and observe the relationship between volume and density.
• Appearance identification: Benzene is a colorless liquid, while benzoic acid is a white solid, which can be initially distinguished by the naked eye.

1. chemical identification method

• acid and alkaline test: Use a glass rod to dip the liquid to be tested, insert the pH test paper rod, and observe the color change. Benzene has a pH of about 6.5, while benzoic acid has a pH of less than 4.
• oxidation reaction test under acidic conditions, benzene can be oxidized to produce benzoic acid. The specific steps are: mixing the liquid to be tested with dilute sulfuric acid, adding manganese dioxide as a catalyst, heating to boiling, and observing whether gas is generated.

1. Solubility test

• take a little of each of the two substances and add them into water respectively to observe their dissolution. Benzene is easily soluble in organic solvents, but not easily soluble in water; benzoic acid is slightly soluble in water, but easily soluble in organic solvents, soluble in water is weak.

1. **spectroscopy Analysis**

• using an infrared spectrum analyzer, the absorption peaks of benzene and benzoic acid are different and can be distinguished by comparing the spectra.

The significance of distinction in the practical application of 5.

In chemical production, benzene and benzoic acid are often used as solvents, catalysts or raw materials. For example:

• benzene: Widely used as organic solvents, such as industrial cleaning, cleaning agents, etc.
• Benzoic Acid: Used in the manufacture of drugs, pesticides or as monomers for polymer materials.

Therefore, it is very important to correctly distinguish between the two in production, storage and use, so as to avoid safety accidents or environmental pollution caused by misuse.

Through the above analysis, we can clearly see the significant differences between benzene and benzoic acid in structure, physical properties and chemical reactions. Mastering these identification methods will help to accurately distinguish these two substances in practical applications and ensure production safety and environmental protection.