Chlorine is a chemical element with atomic number 17, belonging to halogen family. It is the third most abundant element in the earth's crust, second only to oxygen and silicon. Chlorine exists widely in nature, mainly in the form of chloride, such as salt (sodium chloride) and hydrochloric acid.

Chlorine is very active in chemistry and has strong oxidation. It can react with many metallic and nonmetallic elements to generate corresponding compounds. For example, chlorine can react with hydrogen to produce chlorine gas (HCl), sodium to produce sodium chloride (NaCl) and copper to produce copper chloride (CuCl2). In addition, chlorine can react with water to produce hypochlorous acid (HClO) and oxygen.

Chlorine is widely used in industrial production. For example, chlorine is used to prepare various organic compounds, such as plastics, rubber, dyes, drugs and so on. Chlorine is also used for disinfection, bleaching and water treatment. However, excessive chlorine is harmful to the environment and human health, so the use of chlorine must be strictly monitored and managed.

Chlorine is an important chemical element, which has a wide range of uses and important significance. Understanding the nature and application of chlorine will help us to make better use of this resource and protect the environment and human health.

Uses of chlorine:

1. chemical industry: chlorine is mainly used to produce inorganic and organic chlorides, such as sodium hypochlorite, aluminum trichloride, ferric trichloride, bleaching powder, bromine and phosphorus trichloride. It is also the raw material for producing chloroacetic acid, epichlorohydrin, monochlorobenzene and other organic chlorides.

2. Electronics industry: High-purity chlorine gas is mainly used for dry etching, optical fiber, crystal growth and thermal oxidation in electronics industry.

3. Brewery sewage treatment: chlorine can deodorize and remove microorganisms, and the removal rate of biological oxygen consumption and chemical oxygen consumption is also high, which can ensure the stability of circulating water quality and is more suitable for brewery sewage treatment.

4. Disinfection of tap water: Tap water is usually disinfected with chlorine. The disinfection principle is to react with water to generate hypochlorous acid, and the strong oxidation of hypochlorous acid can kill bacteria in water.

5. Pharmaceutical industry: In the pharmaceutical industry, chlorine gas is often used in pharmacy and often participates in the synthesis of chlorine-containing compounds.