What is the main ingredient of a small packet of desiccant that is often placed in a mooncake box?

There are generally three kinds:

1。Quicklime desiccant.

The main component of quicklime desiccant is calcium oxide, and its water absorption capacity is achieved through chemical reaction, so water absorption is irreversible. Regardless of the humidity of the external environment, it can maintain a moisture absorption capacity greater than 35% of its own weight, which is more suitable for low temperature storage, has an excellent drying and moisture absorption effect, and is lower. It can be widely used in food, clothing, tea, leather, shoemaking, electrical appliances and other industries.

2。Silica gel desiccant.

This desiccant is a different variety of silica gel packaged in moisture permeable sachets, the main raw material silica gel is a high microporous structure of hydrous silica, non-toxic, tasteless, odorless, chemically stable, with strong hygroscopic performance. Therefore, it is widely used in the storage and transportation of instruments, meters, equipment, leather, luggage, footwear, textiles, food, medicines, etc. to control the relative humidity of the environment and prevent items from moisture, mildew and rust.

3。Montmorillonite desiccant.

This desiccant is made of pure natural raw material bentonite, which is green and environmentally friendly, non-toxic and tasteless, and has no damage to the human body. It has good adsorption performance at room temperature and general humidity, and has the effects of adsorption activity, static humidification reduction and odor removal. Not only the adsorption speed is fast, the adsorption capacity is high, and it is non-toxic, tasteless, non-contact corrosive, and environmentally pollution-free, especially used in food packaging, which is harmless to the human body.

Scope of application: It is widely used in products that cannot be sealed with oil seal and gas phase, such as: optical instruments, electronic products, medical and health care, food packaging, dry air sealing of military products and civilian products.

The desiccant in food is generally non-toxic, tasteless, non-contact corrosive, and non-environmental pollution; The desiccant in the laboratory such as concentrated sulfuric acid, soda lime, etc. is too dangerous, but they also have advantages, such as extremely fast water absorption, high efficiency, cheap and so on.

For this question, B is chosen because only B can react with water and absorb water.

In fact, the substance in the moon cake box not only removes water, but also removes oxygen, there is also FE powder in it, reducing FE powder, after taking it out, rubbing it in your hand, it will feel radiant, you can do this experiment.

Limestone is carbonated cap caCO3, that is, marble, which is not absorbent. It's common sense.

Quicklime is calcium oxide, which can react with water to produce mature lime, that is, water and calcium hydroxide Ca(OH)2, while caustic soda is sodium hydroxide NaOH discordant reaction.

So choose B

Limestone and hydrated lime do not have water absorption exclusion.

Caustic soda is corrosive and harmful.

Therefore, I chose B downstairs and said that caustic soda does not react with water.

But he's absorbent and in some cases can be used as a desiccant.

However, due to its corrosiveness and other problems, it cannot be used as a food desiccant.

Here is a detailed one, I hope to have your ideal answer.

The principle of use is the principle of galvanic cells in high school (that is, oxygen absorption corrosion):

Fe is the negative electrode, the impurity carbon in Fe is the positive electrode, and air is the electrolyte.

Total reaction that occurs: 4Fe + 302 +6H2O ==4Fe(OH)3 Of course, combined with the knowledge that most of the "corrosion of metal nanometers" belongs to electrochemical corrosion, it can be inferred that the main reaction is the galvanic cell, namely:

Positive electrode (C): 2H2O+O2+4E=4OH - Negative electrode (Fe): Fe-2E=Fe2+

Total reaction: 2Fe + O2 + 2H2O = 2Fe (OH) 2 Subsequent oxidation reaction: 4Fe (OH) 2 + O2 + 2H2O = 4Fe (OH) 3 The basic principle of active iron powder as a "double sorbettor" is provided in some materials

Fe+3 4O2 +3 2H2O Fe(OH)3 Combined with the knowledge of metal rust in high school textbooks, it can be deduced that the complete reaction and noise process is as follows

Fe Fe(OH)3 rust).

In the above reaction process, Fe absorbs O2 and H2O in the packaging bag, so it is called "double absorber".

(1) Calcium oxide reacts with water to form calcium hydroxide, which can be used as a desiccant;

2) The iron in the preservative can absorb oxygen to prevent the moon cake from deteriorating due to oxidation, and the iron reacts with oxygen to form iron oxide, and the text expression of the reaction is: iron + oxygen iron oxide

Therefore, the answer is: (1) water vapor;

2) oxidation; Iron + Oxygen Iron oxides

According to the chemical properties of iron, it can be seen that the powdered substance is iron powder; Iron powder can react with water and oxygen to form rust, which not only absorbs water but also consumes oxygen that can promote the deterioration of food, thereby extending the shelf life of food

So the answer is: iron powder; Iron powder can react with water and oxygen to form rust;