How to Distinguish Formic Acid Acetic Acid Malonic Acid

In the chemical industry, it is very important to distinguish different acidic substances for experimental operation, production safety and product purity control. Formic acid, acetic acid and malonic acid are all acidic substances, but their properties, structures and applications are different. This paper will analyze how to distinguish these three kinds of acidic substances in detail from the aspects of physical properties, chemical properties and practical application.

1. Appearance and smell

The differences in the physical properties of the three acids can help us to distinguish them. Formic acid and acetic acid are colorless liquids, while malonic acid is a colorless transparent liquid. In appearance, the color of malonic acid is closer to that of acetic acid, but on closer inspection, the transparency of malonic acid is slightly higher.

In terms of odor, all three acids have a sour taste, but the odor of malonic acid is slightly more complicated. This is because there are two carboxyl groups in the structure of malonic acid, which makes its intermolecular hydrogen bonds more, resulting in a stronger odor. The smell of formic acid and acetic acid is relatively pure. In contrast, the smell of malonic acid is more reminiscent of fresh apples, because the smell of malonic acid is similar to that of some organic substances.

2. Solubility and stability

Solubility is one of the important indicators to distinguish acidic substances. The solubility of formic acid in water is low, about 0.0018mol/100mL; the solubility of acetic acid is high, about 1.7g/10g water; the solubility of malonic acid is good, but it is easy to decompose at high temperature. The stability of malonic acid is poor, and it is easily decomposed by light, oxidant and reducing agent.

3. Acid strength

The acidity can be judged by the concentration and chemical properties of the acid. The acidity of formic acid is related to its concentration, and the solution with higher dilution is less acidic; the acidity of acetic acid is weak, but it shows strong acidity under specific conditions (such as reaction with certain metals); the acidity of malonic acid is strong, but it is easy to decompose under high temperature or strong oxidation conditions, which limits its practicality.

4. Chemical reaction properties

Formic acid, acetic acid and malonic acid exhibit different reaction characteristics in chemical reactions. When formic acid reacts with alkaline substances, salt and water will be generated; acetic acid will also generate salt and water when reacting with alkaline substances, but the reaction speed is slow; malonic acid reacts with alkaline substances to generate salts with stronger stability, and malonic acid reacts with metals (such as iron, aluminum) will produce hydrogen, and the reaction rate is faster.

Malonic acid shows different characteristics from other acids in some specific reactions. For example, when it reacts with carbonate, malonic acid reacts slowly, which is related to the connection of two carboxyl groups in its molecular structure.

5. Practical application of identification

In practical applications, these three acids can be distinguished by the following methods:

1. Appearance and color: Malonic acid is more transparent, while formic acid and acetic acid are colorless.

2. Odor: Malonic acid has a slightly more complex odor, while formic acid and acetic acid have simpler odors.

3. Solubility test: Add an equal amount of water to the water and see which acid dissolves faster.

4. Chemical reaction experiments: react with alkaline substances or metals (such as iron and aluminum) respectively, and observe the reaction rate and products.

Through the comprehensive analysis of the above properties, formic acid, acetic acid and malonic acid can be accurately separated. This is not only helpful for the correct use of these acidic substances in the laboratory, but also of great significance for the selection and control of acidic substances in industrial production.

The distinction between formic acid, acetic acid and malonic acid requires a comprehensive consideration of physical properties, chemical properties and performance in practical applications. By observing the appearance, smell, testing solubility and chemical reaction experiments, we can fully grasp the characteristics of these three acids. This is of great significance for improving experimental efficiency, ensuring production safety and optimizing process flow.