chlorine

[lǜ]

chemical element

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Chlorine is a Nonmetallic element , element symbol Cl, atomic number 17, located in the third period, family VII A, is Halogen group element one of. Chlorine is composed of two chlorine atoms, chemical formula is Cl two 。 Gaseous chlorine is called chlorine , liquid chlorine is called Liquid chlorine 。 Chlorine is a yellow green gas under normal temperature and pressure, with strong pungent smell, very active chemical property and toxicity. Chlorine exists widely in nature in the form of chemical combination, which is also of great significance to human physiological activities.

Chinese name: chlorine
Foreign name: Chlorine
Appearance: Yellow green gas (chlorine)
Discoverer: Carl Wilhelm Scheele
Element Type: Active non-metallic elements
Atomic number: seventeen

Atomic weight: thirty-five point four five
Element symbol: Cl
Cycle: Third cycle
family: Family VII A
area: Zone p
Electronic layout: [Ne]3s two 3p five
Electronegativity: 3.16 (Pauling scale)

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A brief history of discovery

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Element property data

Swedish chemist in 1774 Scheele Is engaged in Pyrolusite We found that: Pyrolusite And hydrochloric acid When heated, the mixture will produce a suffocating yellow green gas. At that time, the great chemist Lavoisier believed that oxygen was the origin of acidity, and all acids contained oxygen. Scheler and many chemists firmly believe in Lavoisier's view that this yellow green gas is a compound composed of oxygen and another unknown radical, so Scheler calls it "oxyhydrochloric acid". However, David, a British chemist, held a different view. He tried every way to get oxygen out of oxidized hydrochloric acid, but failed. He suspected that there was no oxygen in oxyhydrochloric acid. In 1810, David proved with irrefutable facts that the so-called oxidized hydrochloric acid is not a compound, but a simple substance of a chemical element. He named this element "Chlorine". Its original Greek meaning is "green". The Chinese translation is chlorine.

Natural distribution

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Free chlorine in nature exists in the atmosphere and is one of the main substances that destroy the ozone layer. Chlorine is decomposed into two chlorine atoms (free radicals) by ultraviolet radiation. Most are usually treated with chloride (Cl - ）Exists in the form of sodium chloride (table salt, NaCl).

Origin of name

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The English name chlorine comes from the Greek khlros (χλ ωρ ó ', light green). In Chinese, the word "chlorine" was created by taking the gas as green, while in Japanese and Korean, it is called "salt element" because chlorine is one of the main components of salt ("salt element" is written in Japanese characters).

chemical compound

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Inorganic (valence in parentheses): chloride （-1）、 Hypochloric acid （+1）、 Hypochlorite （+1）、 Chlorite （+3）、 Chlorite （+3）、 chlorine dioxide （+4）^[4] 、 Chlorate （+5）、 Chlorate （+5）、 perchloric acid （+7）、 Perchlorate （+7）

Organochlorine compound 。

isotope

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Chlorine thirty-five Cl and thirty-seven Cl two stable isotope 。 The outermost electron configuration is 3s two 3p five 。 The relative atomic masses are 34.968 852 and 36.965 903, respectively. natural abundance 75.77% and 24.23% respectively.

Inspection of chloride ion

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Check whether the water contains chloride ion, which can be acidified with nitric acid Silver ion (e.g silver nitrate ）(Adding acid silver nitrate can eliminate the interference of other ions), silver ion and chloride ion will react to form Silver chloride White precipitate, reaction formula:

Ag + +Cl - →AgCl↓

Handling and storage

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1. Operation precautions

It shall be tightly sealed to provide adequate local ventilation and overall ventilation. Operators must be specially trained and strictly abide by the operating procedures. It is recommended that operators wear air respirators, mask type adhesive tape gas protective clothing and rubber gloves. Keep away from kindling and heat sources, and smoking is strictly prohibited in the workplace. Keep away from flammable and combustible materials. Prevent gas leakage into the air of the workplace. Avoid contact with alcohols. The cylinder and accessories shall be handled with care to prevent damage. Fire fighting equipment and leakage emergency treatment equipment of corresponding types and quantities shall be provided.

2. Precautions for storage

Store in a cool and ventilated warehouse. Keep away from kindling and heat sources. The storage temperature shall not exceed 30 ℃, and the relative humidity shall not exceed 80%. Should be connected with combustible (Combustibles), alcohols and edible chemicals shall be stored separately, and mixed storage is strictly prohibited. The storage area shall be equipped with leakage emergency treatment equipment. The "five pairs" management system for extremely toxic substances shall be strictly implemented.

physical property

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Chlorine in gas collector

Chlorine is a yellow green gas with a density higher than that of air (3.214g/L), melting point of − 101.0 ℃, boiling point of − 34.4 ℃, and a strong pungent smell.

Chlorine molecule is composed of two chlorine atoms, slightly soluble in water, easily soluble in lye, easily soluble in carbon tetrachloride, carbon disulfide, etc Organic solvent 。

There are 26 isotopes of chlorine, of which only thirty-five Cl and thirty-seven Cl is stable, and other isotopes are radioactive.^[1]

Atomic radius: 100 pm

Extranuclear electron arrangement: [Ne] 3s two 3p five

Schematic diagram of chlorine atomic structure

Valence: ± 1, 3, 5, 7

Crystal structure: Orthorhombic system

Electronegativity: 3.16（ Pauling scale ）

First ionization energy ：1251.2 kJ/mol

Nutritional function

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Participate in photosynthesis

stay photosynthesis As a cofactor of manganese, chlorine participates in the photolysis of water. Water photolysis is the initial photochemical reaction of photosynthesis, and the action site of chlorine is Optical system II 。 The research work showed that under the condition of chlorine deficiency, the proliferation rate of plant cells, leaf area and growth rate decreased significantly (about 60%), but chlorine did not affect the photosynthetic rate in plants. It can be seen that chlorine liberates O from water and light two The effect of the reaction is not direct. Chlorine may be the coordination group of manganese, which helps to stabilize manganese ions and keep them in a higher oxidation state. Chlorine is not only Hill reaction Put O two It can also promote Photosynthetic phosphorylation effect.

Regulate stomatal movement

Chlorine can regulate the opening and closing of pores. When the stomata of some plant leaves open, K + Inflow is caused by Organic acid Anions (mainly malate) act as Companion ion These ions are produced by consuming starch during metabolism; But for some crops with low starch content (such as onions), when K + inflow Guard cell Due to the lack of malate, Cl - As companion ions. In case of chlorine deficiency, onion pores cannot be opened and closed freely, resulting in excessive water loss. Due to the obvious role of chlorine in maintaining cell expansion and regulating stomatal movement, it can enhance the drought resistance of plants.

Activates H+- pump ATPase

In the past, people knew more about H in protoplasm + -ATPase, which receives K + Activation of. There is also H on the vacuole membrane + -ATPase. And H on protoplasm + -Unlike ATPase, this enzyme is not affected by monovalent cations, but activated exclusively by chlorides. This enzyme can convert the H + When transported into vacuoles, pH gradient (cytosol, pH>7; vacuole, pH<<6) is generated inside and outside the vacuole membrane. When chlorine is deficient, the elongation of plant roots is severely blocked, which may be related to the above functions of chlorine. Because chlorine deficiency affects the active solute to penetrate into the vacuole, thus inhibiting the root elongation (Hagerh and Hellnle, 1981).

Control disease occurrence

The application of chlorine containing fertilizer has an obvious effect on inhibiting the occurrence of diseases. It is reported that there are at least 15 varieties of 10 crops before 2013, and their leaf and root diseases can be significantly alleviated by adding chlorine containing fertilizers. For example, take all and stripe rust of winter wheat, leaf rust and leaf blight of spring wheat, root rot of barley, stem blight of corn, hollow disease and brown heart disease of potato, etc. According to the researchers' inference, chlorine can inhibit the nitrification of ammonium nitrogen in soil. When ammonium nitrogen fertilizer is applied, chlorine makes most of ammonium nitrogen unable to be transformed, and forces crops to absorb more ammonium nitrogen; When crops absorb ammonium nitrogen fertilizer, their roots release H + Ions increase the acidity of rhizosphere. Many soil microorganisms are suitable to reproduce in large quantities in the environment with high acidity, thus inhibiting the breeding of bacteria. For example, the application of chlorine containing fertilizers in wheat alleviates the occurrence of take all disease. There are also some researchers from Cl - And NO three - There is competition in absorption to explain. Application of chlorine containing fertilizer can reduce NO in crops three - Concentration, generally NO three - Crops with low content seldom suffer from serious root rot.

Other roles

In many anions, Cl - It is the most stable ion in biochemistry. It can maintain charge balance with cation and maintain osmotic pressure in cells. The fluidity of chlorine in plants is very strong, and the transportation speed is fast, which can quickly enter the cells and increase the osmotic pressure and swelling pressure of cells. The increase of osmotic pressure can enhance the water absorption of cells, and improve the ability of plant cells and tissues to bind water. This is conducive to promoting plants to absorb more water from the outside. Under drought conditions, it can also reduce water loss of plants. The leaf can be upright and the functional period can be prolonged by increasing the puffing pressure. When crops lack chlorine, their leaves often lose their puffing pressure and wilt. Chlorine also has some effect on the buffer system of cell fluid. The role of chlorine in ion balance may have special significance.

Chlorine also affects enzyme activity. Chloride can activate asparagine synthetase using glutamine as substrate, and promote the synthesis of asparagine and glutamic acid. Chlorine plays an important role in nitrogen metabolism.

Appropriate chlorine is beneficial to the synthesis and conversion of carbohydrates.

chemical property

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The outermost electron layer of the chlorine atom has 7 electrons, which is easy to combine one electron in the chemical reaction, making the outermost electron layer reach the stable state of 8 electrons. Therefore, chlorine has strong oxidation and can react with most metals and nonmetals.

Chlorine is disproportionated into hydrochloric acid and hypochlorite when encountering water, and hypochlorite is unstable and easy to liberate free oxygen. Among them, hypochlorite has bleachability (higher than SO two It is strong and the heating does not restore the primary color).

Chlorine can also react with many organic substances in addition or substitution, and is widely used in life.

Chlorine is highly toxic and has been used as a military toxic gas.^[1]

Cl inspection

Check whether there is chlorine ion in the water. Add soluble silver ion (silver nitrate) (adding acid silver nitrate can eliminate the interference of other ions). The reaction of silver ion and chlorine ion will generate silver chloride white precipitate. Then take white precipitate and add dilute nitric acid. If the precipitate is insoluble, it means that it contains chloride ion.^[2]

Oxyacid

one Hypochloric acid (HClO) and its salts

(1) Preparation

① Chlorination in ice water:

② Hypochlorite can be obtained by passing chlorine into alkaline solution:

③ Electrolytic cold concentration for industrial use Salt water And stirred violently to prepare NaClO.

(2) Nature

① Yes weak acid , but it is a strong oxidant and has bleachability

② Easy to happen when heated Redox reaction ：

(3) Purpose

manufacture bleaching powder Ca(ClO)₂：

two Chlorite (HClO ₂) and its salts

Chlorous acid is the only halogen acid, which is very unstable.

(1) Preparation

① ClO ₂ decomposes in water:

② Chlorite can be obtained by adding ClO ₂ to Na ₂ O ₂ or NaOH and H ₂ O ₂:

；

(2) Nature and purpose

① Very unstable compound, but chlorite is relatively stable.

② Bleaching^[1]

three Chlorate (HClO ≮) and its salts

Unstable if the concentration is higher than 40%

(1) Preparation

Hypochlorite The water solution is heated to produce its own redox reaction（ Disproportionation reaction ）：

(2) Nature and purpose

① Chloric acid and Chlorate All Strong oxidant 。

② Potassium chlorate Used to make explosives.

③ KClO ≮ heating reaction:

four perchloric acid (HClO ₄) and its salts

(1) Preparation

① Low pressure distillation of the mixture of KClO ₄ and H ₂ SO ₄:

② Electrolytic salt water The chlorine gas generated by anode is oxidized:

③ Chlorate Thermal decomposition:

(2) Nature and purpose

① The most stable oxy acid of chlorine is not easy to decompose

② Very strong acid (the strongest acid in the high and middle range, stronger than 100% sulfuric acid, but weaker than HSbF etc. Superacid ）

Main purpose

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Industry

Chlorine is mainly used in the chemical industry, especially in the organic synthesis industry, to produce plastics synthetic rubber , dyes and other chemicals or intermediates, also used for bleaching agents 、 disinfectant 、 Synthetic drugs Etc. Chlorine is also used to manufacture bleaching powder, bleach pulp and cloth, synthesize hydrochloric acid chloride , drinking water disinfection, synthetic plastics and pesticides, etc. refine Rare metals It also needs a lot of chlorine.

physiology

Chlorine is necessary for human body Constant element One is to maintain body fluid and electrolyte It is necessary for balance and an essential component of gastric juice. In nature, it often exists in the form of chloride, and the most common form is table salt. The average content of chlorine in human body is 1.17g/kg, and the total amount is about 82~100g, accounting for 0.15% of the body weight, which is widely distributed throughout the body. The main form of monochloride ion is combined with sodium and potassium. among potassium chloride Mainly in intracellular fluid, while sodium chloride mainly in Extracellular fluid Medium.

The dietary chlorine comes almost entirely from sodium chloride and only a small amount from potassium chloride. Therefore, salt and its processed food soy sauce, cured meat or smoked food, pickles and salty food are rich in chloride. The content of chlorine in general natural food varies greatly; Almost all natural water also contains chlorine.^[1]

Main physiological functions:

1. Maintain body fluid acid-base balance 。

Chloride ion analyzer

2. Chloride ion and sodium ion are the main ions in extracellular fluid to maintain osmotic pressure. They account for about 80% of the total ions, and regulate and control the capacity and osmotic pressure of extracellular fluid.

3. Chloride ions also participate in the formation of gastric acid in gastric juice, and gastric acid promotes vitamin B twelve And iron absorption; activation Salivary amylase Decompose starch and promote food digestion; Stimulate the liver function and promote the excretion of metabolic waste in the liver; Chlorine can also stabilize the membrane potential of nerve cells.

safety protection

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Chlorine has irritating effect on eyes and respiratory mucosa, which can cause respiratory symptoms such as tears, cough, cough with a small amount of sputum, chest tightness, tracheitis, bronchitis, pulmonary edema, and even shock and death in serious cases. During the First World War, it was used as a chemical weapon (suffocating agent).

Chlorine is harmful to the environment and can pollute water.

At the same time, chlorine can support combustion, and wet chlorine is highly corrosive.

Therefore, when contacting chlorine, it is necessary to pay attention to the strict protection of the whole body. It is strictly prohibited to smell and contact chlorine directly, and it is not allowed to directly discharge chlorine containing waste gas into the atmosphere.^[3]

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