Remarkable Chlorine/Cl2: Properties, Synthesis, Reactions and Applications

With the atomic number 17 and the chemical symbol Cl, chlorine is a very reactive chemical element. It is categorized as a nonmetal and belongs to the periodic table’s halogen group. Chlorine is a gas that has a strong smell similar to that of bleach and is a light-yellow green in its pure state. It is a highly toxic gas that occurs at room temperature and pressure. It is also extremely reactive. It is frequently utilized in a variety of industrial, commercial, and home applications because of its potent disinfection characteristics.

In nature, it does not occur as a free element because it is extremely reactive, but it is present in large quantities as chloride salts. Carl Wilhelm Scheele, a Swedish chemist, made the discovery of chlorine in 1774. It is made by electrolyzing brine, a mixture of water and sodium chloride. During this process, chlorine gas is generated at the anode.

Environmental effects are possible with chlorine and its byproducts. Trihalomethanes (THMs), which have been linked to potential health problems, are toxic disinfection byproducts (DBPs) that can occur when chlorine is released into water bodies. Through adequate water treatment and chlorine dosage management, DBP production is minimized.

Physical properties:

  1. Density: Higher than air (1.56g/cm3)
  2. Melting point: Chlorine melts at -101.5 oC.
  3. Boiling point: Its boils at -34.04 oC.
  4. Solubility: Its forms a strong oxidizing solution called chlorine water and is highly soluble in water.

Chemical properties:

1. Reactivity: Chlorine easily interacts with other elements and compounds due to its strong reactivity. It is an effective oxidizer.

2. Disinfectant: Its has strong disinfectant properties because of its capacity to eliminate bacteria, viruses, and other germs. The disinfecting effects of chlorine are due to a weak acid termed hypochlorous acid that is created when chlorine dissolves in water.

3. Oxidizing Agent: Its has the ability to interact with a variety of substances, serving as an oxidizing agent and generating chemical changes.

4. Reaction with Organic Substances: Hydrocarbons and chlorine react to generate chlorinated compounds. Plastics, solvents, and insecticides are all produced using this process.

Synthesis/ Production:

The electrolysis of brine (saltwater) and the thermal dissolution of metal chlorides are the two main mechanisms that produce chlorine. The thorough synthesis procedures for chlorine are as follows:

Brine electrolysis (Diaphragm Cell Process):

Brine, a sodium chloride (NaCl) solution in water, serves as the starting point for this procedure. A diaphragm cell, which consists of a split compartment with a porous diaphragm separating the anode and cathode, is used to electrolyze brine. Chloride ions (Cl-) from the brine move to the anode (positive electrode) and undergo oxidation to produce Cl2 gas when an electric current is run through the cell. On the cathode (negative electrode), sodium ions (Na+) from the brine undergo reduction to produce sodium hydroxide (NaOH). For later usage, the chlorine gas produced at the anode is collected and purified.

Electrolysis of brine (Membrane cell process):

Due to its effectiveness and environmental benefits, this technology is currently the most widely used for producing chlorine. The anode and cathode compartments are divided using a selectively permeable membrane in this technique. Cl2 gas is produced directly at the anode because of the membrane’s ability to let sodium ions pass through while preventing chloride ions from doing the same. As a byproduct, sodium hydroxide is created at the cathode.

Mercury Cell Process:

In the past, it was produced by electrolyzing brine in a cell with a mercury cathode. Due to environmental concerns, it is no longer used. While sodium amalgam (a combination of sodium and mercury) was synthesized at the cathode, chlorine gas was produced at the anode. The mercury was then restored for further use by reacting the sodium amalgam with water to produce sodium hydroxide.

Metal chlorides thermally decompose:

The thermal breakdown of metal chlorides like calcium chloride (CaCl2) or hydrogen chloride (HCl) can also produce chlorine. Cl2 gas is released when the metal chloride is heated to high temperatures. Using this method on a large scale to produce chlorine is less prevalent.

Chemical reactions:

  1. Disproportionation Reaction:

Chlorine disproportionately reacts in the presence of water to produce HCl and hypochlorous acid. Processes for chlorinating and disinfecting water depend on this reaction.

Cl2 + H2O → HCl + HOCl

  1. Reaction with Metals:

Metal chlorides are created when chlorine interacts with metals like sodium. In this illustration, sodium and Cl2 interact to form sodium chloride (NaCl).

2Cl2 + 2Na → 2NaCl

  1. Reaction with Hydrogen:

Cl2 reacts with hydrogen to form hydrogen chloride (HCl), which is a corrosive acid.

Cl2 + H2 → 2HCl

  1. Reaction with Organic Compounds:

It can engage in substitution reactions with organic molecules, especially those that include hydrogen atoms. Plastics, insecticides, and pharmaceutical manufacturing are just a few of the industrial processes that exploit these reactions. Additionally, it combines with organic substances like body oils, perspiration, and urine to produce combined chlorine or chloramines. Chloramines may produce unpleasant odors, ocular discomfort, and irritation on the skin. To solve this, the chloramines are oxidized, and the disinfectant properties of chlorine are restored using a procedure known as super-chlorination or breakpoint chlorination.

  1. Reaction with Alkenes:

It can react with alkenes, such as ethene (C2H4), in an addition reaction to form a dichloroalkane. In this example, Cl2 reacts with ethene to produce 1,2-dichloroethane.

Cl2 + C2H4 → C2H4Cl2

  1. Reaction with Oxygen:

Chlorine dioxide (ClO2), a potent oxidizing agent used in water treatment and bleaching procedures, is created when Cl2 combines with oxygen gas (O2).

2Cl2 + O2 → 2ClO2

  1. Reaction with Ammonia:

Nitrogen gas (N2) and ammonium chloride (NH4Cl) are created when Cl2 interacts with ammonia (NH3). Fertilizers with an ammonium base are made using this reaction.

8NH3 + 3Cl2 → 6NH4Cl + N2


Cl2 has numerous applications across various industries. Some of the major applications of chlorine are:

  1. Manufacturing of chemicals: It is a crucial component in the manufacturing of a variety of chemicals. Numerous organic and inorganic chemicals, such as PVC (polyvinyl chloride), solvents, bleach, chlorinated rubber, insecticides, and medications, are produced using it.
  2. Bleaching and cleaning: Surfaces are disinfected, and fabrics and paper items are bleached using chlorine chemicals, such as sodium hypochlorite. Cleaning agents with chlorine are good in getting rid of bacteria, mould, and stains.
  3. Pharmaceuticals: Several pharmaceutical goods, such as antibiotics, antiseptics, and painkillers, are made using Cl2. In the pharmaceutical business, it’s also employed as a disinfectant to clean tools and packaging.
  4. Immune system: Neutrophils are immune cells that create chlorine compounds, such as hypochlorous acid, to combat invasive invaders. These substances function as antimicrobial agents, aiding in the destruction of germs and defending the body against illnesses.
  5. Chlorophyll formation: Chlorophyll, the pigment that gives plants their green color, is partially created by chlorine. Magnesium is found in the center of chlorophyll molecules, which are encircled by a ring of carbon, nitrogen, and hydrogen atoms. Cl2 helps to create this ring structure, which enables the synthesis of chlorophyll.
  6. Water treatment: It is frequently used to clean and disinfect water. Water is made safe for drinking and swimming by killing bacteria, viruses, and other germs effectively. Cl2 is added to public water supplies, swimming pools, and wastewater treatment plants.
  7. Plastics and polymers: The manufacturing of PVC, a multipurpose plastic used in pipes, window frames, flooring, and electrical insulation, requires Cl as a key ingredient. Other polymers and resins are produced using Cl2 as well.
  8. Agriculture: Herbicides and insecticides with a chlorine base are used in agriculture to prevent the growth of pests and weeds. It is also used to make fertilizers and as an ingredient in animal feed.
  9. Paper industry: In the production of pulp and paper, Cl2 compounds are utilized in the bleaching process. They assist in removing lignin and color from wood fibers to produce paper that is brilliant and white.
  10. Ozone Layer Depletion: It has been determined that chlorine-containing substances, in particular chlorofluorocarbons (CFCs), are one of the main causes of ozone layer depletion. Once these substances are released into the atmosphere, they may break down ozone molecules, causing the ozone layer to thin.
  11. Textiles: Bleaching and finishing procedures in the textile sector employ Cl2. It aids in cleaning clothes of pollutants, stains, and undesirable colors.
  12. Swimming pool: It is frequently used to sanitize swimming pools and preserve water quality. In pool water, it aids in the destruction of bacteria, algae, and other microbes. Swimming pool water is frequently treated with chlorine in the form of liquid chlorine (sodium hypochlorite), solid chlorine (calcium hypochlorite), or Cl2 gas. When these forms are dissolved in water, hypochlorous acid (HOCl) is released, which is the active disinfecting agent.
  13. Pharmaceuticals: Various pharmaceutical goods, such as antibiotics, antiseptics, and painkillers, are produced using Cl2. In the pharmaceutical business, it’s also employed as a disinfectant to clean tools and packaging.

Taking safety into account

  • Use the proper protection equipment during the handling of Cl2. By doing this, chlorine gas or liquid is less likely to come into direct contact with the skin, eyes, or respiratory system.
  • To reduce exposure to chlorine gas, work in well-ventilated spaces or make use of local exhaust ventilation systems. Never use Cl in a small area without adequate ventilation.
  • Treat chlorine bottles gently and prevent dropping or hard handling. It should be kept away from heat, direct sunlight, and incompatible materials in a cold, dry place with good ventilation. Follow safe storage practices and keep chlorine away from sources of ignition and combustible materials.
  • Check equipment, pipelines, and containers frequently for leaks. Even tiny leaks of Cl gas can be identified by their characteristic odor. If a leak is found, leave the area immediately and call the relevant authorities.


In conclusion, chlorine has many industrial applications and it is a very important element in numerous sectors due to its versatility, compound-forming abilities, and disinfectant characteristics. To guarantee the security of anyone working with or around chlorine, it should be handled carefully.

Is chlorine essential for Life?

Life cannot exist without chlorine. It is an essential part of the chloride ion (Cl-), which is crucial for many biological functions. In the human body, chloride ions help to sustain nerve and muscle function, regulate pH levels, and keep fluid equilibrium. It contributes to photosynthesis, which is how plants turn sunlight into energy. During the light-dependent stage of photosynthesis, it participates in the water-splitting reaction, helping to produce the oxygen and electrons required for generating energy.