Chemical Difficult Questions, Questions & Answers

In the preparation experiment of ethyl acetate, in the small test tube in which the product is collected, the catheter cannot contact the liquid level, let alone extend below the liquid level. The analysis of the test center is that if it penetrates below the liquid level, it will hinder the export of the product. There is a difference with the expression of anti-reverse, is there a problem with this statement?

Opinion 1: According to the three effects of saturated sodium carbonate solution, there is no problem.

Point 2: Does not hinder exporting.

Editorial opinion:

1. Regarding the location of the catheter port

Several versions of middle school chemistry textbooks I have seen show that the catheter port is not inserted below the liquid level in small test tubes. However, there are also previous publications of "Middle School Chemistry Experiments Daquan" (P384) in which the catheter port is inserted below the liquid level. Personally, I think it is more reasonable for the catheter not to be inserted below the liquid level. The reasons are as follows:

1. When not inserted below the liquid level, there is no inversion phenomenon because the catheter port is not in contact with the liquid level. If inserted below the liquid level, there is a risk of inversion.
2. When not inserted below the liquid level, the liquid or gas can flow out smoothly from the conduit. If inserted below the liquid level, a closed system is formed, and the pressure in the system must be greater than the external environment, which poses certain safety risks.
3. When not inserted below the liquid level, the gas (air) derived from the catheter port can take away some of the heat. If inserted below the liquid level, the heat is absorbed by the solution in the small test tube, which increases the temperature of the solution and accelerates the volatilization of the product.

Second, the problem of reverse suction

Personally, I believe that whether the phenomenon of reverse suction can be produced in the experiment may also be related to the heat source and heating method of heating:

1. About heat sources: There are currently two heating methods in different versions of textbooks, one is direct heating, and the other is water bath heating. During direct heating, the temperature rises quickly, the temperature is higher, and the experimental time is short, resulting in a large water-soluble gas component in the evaporated gas, which is easy to cause inversion; while the water bath heats up slowly, the temperature is low, and the evaporated gas has less water-soluble components, which is not easy to cause inversion.
2. About the heating method: water bath heating, the heating is gentle, generally does not occur when the temperature is high and low, but when directly heated, the heating is fast, and the flame will also be affected by the ambient air flow, causing the flame to swaying. The temperature of the test tube may fluctuate, which is more likely to cause inversion.

III. Comparison of the preparation of ethyl acetate and butyl acetate

High school chemistry has two more important esters (ethyl acetate and butyl acetate) preparation experiments, we can analyze and compare from the following aspects:

Among them, due to the different temperature conditions required for the two reactions, the heating methods of the two experiments are also different. The preparation temperature of ethyl acetate can be controlled at about 100 ° C, and water bath heating is used to make it evenly heated; the preparation temperature of butyl acetate needs to be about 115~ 125 ° C, and water bath heating cannot be used. In order to prevent dehydration and carbonization at high temperature, hot air bath is used for heating.

The difference in the purification methods of the two experimental products is related to the difference in the comparison of the boiling points of the raw materials and products required for the preparation of ethyl acetate and butyl acetate. The boiling point of ethyl acetate is lower than that of the reactants and can be distilled and purified while reacting; the boiling point of butyl acetate is higher than that of the reactants, and can only be prepared by continuous condensation and reflux, and then the product can be purified.