Topic 1 Common salt in daily life

Topic 1

common salt in life

The salt mentioned in daily life usually refers to table salt (the main component is NaCl) ; while the salt in chemistry refers not only to table salt, but to a class of compounds containing metal ions and acid radical ions, such as sodium chloride , copper sulfate, calcium carbonate, etc. In our country, there have been many poisoning incidents caused by misusing industrial salt such as sodium nitrite (NaNO2 ) as table salt for cooking.

In addition to table salt, common sodium carbonate ( Na2CO3, commonly known as soda ash, soda), sodium bicarbonate ( NaHCO3 , commonly known as baking soda), potassium permanganate ( KMnO4 , etc.) are all salt; the main component of limestone and marble is calcium carbonate. (CaCO3 ) is also a salt.

1.sodium chloride

Sodium chloride is an important condiment. If you don't put salt when cooking, the dishes will be tasteless. Sodium chloride is also essential for normal physiological activities of humans. Most of the sodium chloride contained in the human body exists in body fluids in the form of ions. Sodium ions play a major role in maintaining the normal water distribution inside and outside cells and promoting the exchange of substances inside and outside cells; chloride ions are the main component in gastric juice, which can promote the production of hydrochloric acid, help digestion and increase appetite. People will take in some salt every day to supplement the sodium chloride discharged due to sweating, urination, etc., to meet the normal needs of the human body (about 3 to 5 g of salt per person per day). But long-term consumption of too much salt is not conducive to human health.

Sodium chloride has many uses. For example, medical saline is prepared with sodium chloride; in agriculture, sodium chloride solution can be used to select seeds; in industry, sodium chloride can be used as raw material to produce sodium carbonate, sodium hydroxide, chlorine and hydrochloric acid, etc. . In addition, vegetables, fish, meat, eggs, etc. can also be pickled with salt. The pickled food not only has a unique flavor, but also prolongs the storage time. Snow on roads can also be removed with sodium chloride, etc.

Sodium chloride is widely distributed in nature. In addition to seawater containing a large amount of sodium chloride, salt lakes, salt wells and salt mines are also sources of sodium chloride.

By drying seawater or boiling salt well water, salt lake water, etc., water can be evaporated to obtain coarse salt. Coarse salt contains a variety of soluble impurities (magnesium chloride, calcium chloride, etc.) and insoluble impurities (sediment, etc.). Coarse salt can be preliminarily purified by dissolving, precipitating, filtering, evaporating, crystallizing, etc.

2.Sodium carbonate, sodium bicarbonate and calcium carbonate

In industry, sodium carbonate is widely used in the production of glass, paper, textile and detergent, etc. The main component of naturally occurring limestone and marble is calcium carbonate, which is an important building material. Many pillars in the Great Hall of the People and the Huabiao in front of Tiananmen Square are made of marble; calcium carbonate can also be used as a calcium supplement. Sodium bicarbonate is one of the main ingredients of baking powder used in baking pastries; medically, it is an agent for the treatment of hyperacidity.

When learning how to make carbon dioxide, we already know that calcium carbonate can react with hydrochloric acid

Analyzing the above reactions, they all take place in a solution, and are reactions in which two compounds exchange components to form two other compounds. Such a reaction is called a metathesis reaction .

3.Conditions for the double decomposition reaction to occur

1.Are the above two reactions a metathesis reaction? What do the observed phenomena have in common?

2.Is the acid-base neutralization reaction learned earlier also a metathesis reaction?

Among the products of the neutralization reaction, what is the same product?

3.What are the common phenomena that can be observed when salts containing carbonate groups such as sodium carbonate and calcium carbonate react with hydrochloric acid?

Acids, bases, and salts do not all undergo metathesis reactions. Only when the two compounds exchange components with each other, and there is precipitation or gas or water in the product, the metathesis reaction can take place.

After finishing this topic, you should know

1.Salts such as sodium chloride, sodium carbonate, sodium bicarbonate and calcium carbonate are widely used in life and production.

2.The mixture can be separated by filtration, evaporation, etc., eg, to purify the crude salt.

3.Salts containing carbonate ions or bicarbonate ions ( HCO ; ) in their composition can react with hydrochloric acid to generate carbon dioxide gas.

4.Metathesis reactions can occur between salts, acids, and bases, and the conditions for the reactions to occur are precipitation or the generation of gas or water.