How to distinguish between propionic acid and acetic acid

In the chemical industry, the identification of chemical substances is very important. Among them, propionic acid and acetic acid are often confused as common organic acids. This article will analyze in detail how to distinguish these two substances from multiple perspectives to help readers better understand and apply them.

1. Molecular Structure Differences

The molecular formulas of propionic acid and acetic acid are C3H4O3 and C2H4O2, respectively, and their molecular weights are 72 and 60, respectively. The molecular structure of propionic acid has a carboxylic acid group and a hydroxyl group, while the molecular structure of acetic acid has only one carboxylic acid group. This structural difference leads to many differences in their properties.

In the molecule of propionic acid, the hydroxyl group replaces the second carbon of the carboxylic acid group in acetic acid, making propionic acid more acidic than acetic acid. The position and number of hydroxyl groups in the molecular structure of propionic acid also affect their physical and chemical properties.

2. physical property differences

1. different boiling points The boiling point of propionic acid is 141°C, while the boiling point of acetic acid is 78°C. This significant temperature difference can help to distinguish between the two by means of heating or evaporation. Propionic acid requires a higher temperature to separate its molecules, while acetic acid evaporates easily at lower temperatures.

2. density difference Propionic acid has a slightly higher density than water (about 1.046g/cm³), while acetic acid has a slightly lower density than water (about 0.962g/cm³). These two substances can be distinguished by measuring the density of the solution, especially in mixtures involving water.

3. chemical differences

1. Acid strength Propionic acid is more acidic than acetic acid, which can be identified by the rate of reaction with the metal. In the table of metal activity order, propionic acid is more acidic than acetic acid, so the rate of metal reaction with propionic acid is faster.

2. Different reaction products In the hydrolysis reaction of propionic acid, ethanol, acetaldehyde and acetic acid can be produced. The hydrolysis of acetic acid produces ethanol and acetic acid. The products of these two reactions are different and can be used as a basis for distinction.

4. Application Areas Differences

1. industrial production Propionic acid and acetic acid have different applications in industrial production. Propionic acid is commonly used to produce ethyl acetate, acetone and other organic compounds, while acetic acid is mainly used to produce ethanol and ethyl acetate.

2. Daily Life In daily life, acetic acid is often used in fruit wine production and food preservation, while propionic acid is mainly used in pharmaceutical synthesis and the production of some special materials.

Conclusion

Through the above analysis, we can draw the main method to distinguish between propionic acid and acetic acid: first observe their molecular structure, the molecular formula of propionic acid is more complex; distinguish by boiling point and density; judge according to the strength of acidity and reaction products. Mastering these methods can help us accurately distinguish these two substances in practical applications, thereby making better use of their properties and uses.