Differentiating acetaldehyde by chemical method

In the chemical industry, the identification and differentiation of substances is a basic and important task. As an important organic compound, acetaldehyde (CH3CHO) is often confused with other similar molecules (such as formaldehyde, formaldehyde, ethanol). This article will analyze in detail how to identify the difference between acetaldehyde and other substances through chemical reactions and reagents from the perspective of chemical methods.

Overview of 1. identification methods

chemical identification is an important means to identify the species of substances through their unique chemical reaction characteristics. For the identification of acetaldehyde, a variety of methods such as color change, physical properties and chemical reactions can be used. The following are several common chemical identification methods:

1. Coverage identification method

covering type identification method distinguishes the characteristic reaction of substances from other substances by selective reaction. For the identification of acetaldehyde, the following steps can be used:

• reagent selection use bromine water or acidic potassium permanganate solution.
• Operation steps:

1. the sample to be tested is mixed with the reagent.
2. Observation phenomenon: if the solution fades, it may be acetaldehyde; if bubbles or solution color changes, it may be other substances.

• Theoretical basis: Acetaldehyde molecule contains aldehyde group (CHO). Under acidic conditions, aldehyde group is easy to react with bromine water to generate unstable intermediates, which eventually leads to fading. Other substances (such as formaldehyde, formaldehyde) may react with reagents in different ways, or the reaction is not complete, and the fading cannot be completed.

2. Layering and color change method

when acetaldehyde is mixed with water, two layers of liquid are formed due to the different intermolecular forces. By observing the delamination and color change, it can assist in the identification of acetaldehyde.

• Operation steps:

1. the sample to be tested is mixed with water.
2. Stir until let stand.
3. Observe the layering: the upper layer is colorless transparent liquid, and the lower layer may be light yellow or colorless.

• Theoretical basis the density of acetaldehyde is slightly lower than that of water, so it will float in the water layer; while the density of other substances such as formaldehyde and formaldehyde may be similar, and other methods should be combined for identification.

3. Oxidation test

as a highly reductive aldehyde compound, acetaldehyde can be further identified by oxidation tests.

• Reagent selection biuret reagent.
• Operation steps:

1. the sample to be tested is mixed with the biuret reagent.
2. Add water to swell and let stand.
3. Observe the color change: if it appears purple, it is acetaldehyde.

• Theoretical basis: Aldehyde compounds have reducibility, which can make the addition reaction of CN-ion of biuret reagent to generate purple complex.

2. reagent selection and operation steps

the key to the identification of acetaldehyde is to select the appropriate reagent. The following reagents are commonly used identification reagents:

1. acidic potassium permanganate solution: Used for oxidation test, capable of strong oxidation reaction with aldehyde group to generate soluble ions.
2. bromine water: Used for covering type identification, auxiliary identification through fading phenomenon.
3. Biuret reagent: Used to detect the presence of aldehyde groups and assist in identification by color change.

3. Precautions and error analysis

in the process of chemical identification, the following points should be paid attention:

1. scope of use of reagents: Some reagents are only suitable for specific substance ranges and should not be confused.
2. Operation Specification: Avoid residual contamination of reagents and ensure the accuracy of experimental operations.
3. Environmental Control chemical experiments need to be carried out in a sterile and non-toxic environment to avoid other impurities interfering with the results.

4. Conclusion

through the chemical method to identify acetaldehyde, can effectively distinguish its similar substances. The selection of suitable reagents and operation steps is the key to the identification work. Acidic potassium permanganate solution and bromine water are commonly used reagents, which can be identified by color change and fading phenomenon. The biuret reagent further confirms the presence of an aldehyde group by a purple reaction. Through the comprehensive use of a variety of chemical identification methods, the accuracy and reliability of substance identification can be improved. In practical application, the most suitable identification method should be selected according to the specific situation.