In chemical organic experiments, why can adding broken porcelain pieces prevent boiling?

Pure liquids lack a vaporizing core, and the thermal hysteresis phenomenon of heating beyond the boiling point and still not boiling - after adding a little impurity (essentially bringing in tiny bubbles), the boiling hysteresis is broken and boiling is produced. The bubbles in the liquid play the role of vaporizing the nucleus during boiling, and when there is a lack of bubbles in the liquid, it does not boil even if the temperature reaches and exceeds the boiling point, forming a superheated liquid. Superheated liquids are unstable, and if the external ambient temperature of the superheated liquid drops sharply or invades the bubbles, it will form a violent boiling accompanied by a popping sound, this phenomenon is called boiling The result of boiling is to bring the temperature of the liquid back to the boiling point Boiling is sometimes dangerous.

The principle of adding broken porcelain tiles to the liquid is the same as adding impurities, mainly through the pores to condense water vapor, so that the bubbles float out to prevent boiling.

When boiling, because the bottom temperature of the experimental vessel is very high, the water (liquid) in contact with it will immediately evaporate into water vapor, so there will be a large number of bubbles, so that the boiling will be bursting, and the liquid will continue to tumble, so it is easy to overflow the items of chemical reaction, and the reaction effect will be weakened or harmful to the human body. Add broken porcelain because it is relatively heavy, the boiling water vapor will slow down its gushing speed when it encounters the porcelain piece, and in this process, the water vapor cools and turns into water, so that the gas is reduced, and the boiling situation disappears accordingly.

During reheating, bubbles form in the boiling water. In general, bubbles are very large because they contain a lot of energy. Add crushed stone blocks to make the bubbles smaller.

When a porous object is added, such as zeolite crushed porcelain pieces, the bubbles produced when the liquid boils become small and uniform through the small pores without causing a boiling.

After adding the porcelain tiles, it is heated more evenly.

Prevent overboiling

The bubbles or impurities in the liquid play the role of vaporizing the nucleus during boiling. (Only when there is a vaporized nucleus in the liquid, the liquid above the boiling point can vaporize around the vaporized nucleus to form bubbles, which is called liquid boiling.) When there is a lack of bubbles or impurities in the liquid, it does not boil even if the temperature reaches and exceeds the boiling point, forming a superheated liquid.

Superheated liquids are unstable, if the external ambient temperature of superheated liquids drops suddenly and sharply or invades bubbles or impurities, it will form a violent boiling, accompanied by a popping sound, this phenomenon is called boiling The result of boiling is to bring the temperature of the liquid back to the boiling point. Boiling is sometimes dangerous, and bubbles or impurities in the liquid should be added to prevent it from occurring.

There are many occasions and types that are easy to cause boiling, and there are two kinds of rough classification:

1) "Burst boiling" caused by heat of dissolution + heat of vaporization: If water is poured into concentrated sulfuric acid during misoperation, the heat released when the two are miscible meets the heat of vaporization of the water, but it is not evenly exported, resulting in "burst boiling";

2) "Burst boiling" caused by the heat of vaporization: such as "burst boiling" caused by cold water dripping into hot oil;

To prevent overboiling, place a few pieces of broken porcelain or a few pieces of zeolite at the bottom of the round-bottom flask. Zeolite contains gases in its microporous structure, which forms a gasification center.

In middle school, if you understand it this way, for the broken porcelain tiles added in A, if it does not have a catalytic effect, then it is meaningless to add it. Therefore, broken porcelain pieces can only play a catalytic role.

For zeolite in C, it may or may not be catalytic. Because zeolite can also resist storm boiling, at least manganese dioxide is more like a catalyst.

Strictly speaking, this title does not show that the broken porcelain piece in A plays a catalytic role.

Because there is no comparative experiment to show that the decomposition rate of the broken porcelain tiles is faster than that of the unbroken porcelain tiles.

The same does not mean that the zeolite in c has a catalytic effect.

Judging by the number and time of the occurrence of reaction products, if there are many products and the flame is strong, it proves that the objects in the device have the role of catalysts, and the essence of catalysts should be to accelerate the rate of chemical reactions.

For this question, you just need to remember that adding broken porcelain and MNO2 can play a catalytic role, and the specific reason is that you will know when you are admitted to university and study molecular chemistry.

Due to the porous silicate nature of zeolite, there is a certain amount of air in the small pores, which is often used for anti-storm boiling. When heated, the air inside the small hole escapes, which acts as a vaporizing nucleus, and small bubbles are easily formed on its corners.

Broken porcelain pieces are also porous silicates, which can be used as zeolite, which can provide a vaporization center for liquid boiling, which is due to the fact that zeolite contains many capillaries, in which there is gas, when heated and boiled, the gas is heated and escaped, providing a vaporization center, thereby preventing overboiling. Therefore, many porous materials can be used as zeolite, such as broken porcelain pieces.

Broken porcelain is an irregularly shaped solid, there are many edges and corners on it, bubbles are formed at different edges and corners, it avoids the bubbles concentrated in one place, and large bubbles will be formed in one place, and when heating the liquid, there is the formation of large bubbles, so when heating the liquid, the broken porcelain pieces are added to disperse the formation of bubbles and can prevent the boiling.

Because there are many small holes in the broken porcelain piece, it can carry air bubbles in the liquid. When heated, it prevents boiling.