Chlorine Gas




Chlorine is an element in Group 7 of the Periodic Table. Members Group 7 are also known as Halogens.

Each chlorine atom consists of 17 protons, 17 electrons plus a quantity of neutrons whose exact number depends on the particular isotope of chlorine (in most cases there are 18 neutrons in each atom of chlorine).

Chlorine gas is the elemental form of the chemical element chlorine at standard temperature and pressure.

Chlorine gas consists of molecules, rather than atoms of chlorine.
Two atoms of chlorine (described below) form each molecule of chlorine, hence molecules of chlorine are said to be diatomic and the chemical symbol for chlorine gas is Cl2.

Chlorine gas is approx. 2.5 times heavier than air so it tends to accumulate at the bottom of poorly ventilated spaces such as boxes, containers or parts of rooms/laboratories. Chlorine gas is highly toxic and irritates the respiratory system.

Discovery of Chlorine Gas

Swedish pharmacist Carl Wilhem Scheele is credited with the "discovery" (first observation) of the element chlorine gas (Cl2) because in 1774 he released a few drops of hydrochloric acid onto a piece of the mineral pyrolusite, whose chemical name is manganese dioxide. The result was a greenish-yellow gas that he called "dephlogisticated muriatic acid air" and which later became known as "chlorine". Initially Scheele thought that the greenish-yellow gas he observed was an oxide produced as a result of a reaction of the mineral with the hydrochloric acid. The identity of this greenish-yellow gas as an element was not established until 1810 when the English chemist Sir Humphrey Davy tried to decompose the "dephlogisticated muriatic acid air" by reacting it with charcoal to release the free element "muriaticum" (which is not a real element but rather the name given by Scheele to the element whose oxide he thought had been released in the form of the greenish-yellow gas) and carbon dioxide. Sir Davy concluded from his experiements that the greenish-yellow gas was not, in fact, an oxide or any other compound but rather an element and suggested the name "chloric gas" or "chlorine" based on the Greek word khloros, which means "greenish-yellow".

Health effects of Chlorine Gas

The toxicity of chlorine it due to its oxidizing power.

When chlorine is inhaled at concentrations above 30 ppm, it begins to react with water and the cells of the body, which change it into hydrochloric acid (HCl) and hypochlorous acid (HClO). Coughing and vomiting may occur at 30 ppm and lung damage at 60 ppm. Chlorine gas is said to "sting" the back of the throat and chest and reacts with the water present in the mucosa of the lungs to form hydrochloric acid, which can be lethal. Approx 1000 ppm of chlorine can be fatal after just a few deep breaths. Even breathing in only lower concentrations can irritate the respiratory system, while exposure to the gas can irritate the eyes.

Isotopes of Chlorine

Chlorine gas can consist of atoms of any isotopes of chlorine.

Chlorine has several isotopes, the most common and stable of which are 35Cl, commonly referred to as "chlorine 35" and 37Cl, commonly referred to as "chlorine 37". Typical proportions of these are 75.77% 35Cl and 24.23% 37Cl, hence the atomic mass of chlorine is often stated as 35.5. (That is, 35 x 75.77/100 + 37 x 24.23/100 = 35 x 0.7577 + 37 x 0.2423 = 26.5195 + 8.9651 = 35.4846, which is approximately equal to 35.5)

Uses of Chlorine (Gas)

  • Chemical Weapons (Historically):
    Chlorine gas (also known as "bertholite") was used as a chemical weapon during World War I. The damage caused by chlorine gas (see the section "Health effects of Chlorine Gas" above) can be prevented by a gas mask or other filtration method. After its first use, chlorine was used as a chemical weapon by both sides in WWI but it was soon replaced by the more deadly gases.

Uses of Chlorine (including chlorine combined with other elements to form compounds of chlorine)

  • Bleaching and Disinfectants (in general): Disinfectants that include the chemical element chlorine are used against many different dangerous germs in both domestic house and public places such as hospitals, swimming pools, hotels and restaurants. Chlorine's powerful disinfectant qualities are due to its ability to bond with and destroy the outer surfaces of bacteria and viruses.
    Historically: Chlorine was first used as a germicide in the maternity wards of Vienna General Hospital in Austria in 1847 and became one of humanity's fiercest weapons against a wide range of life-threatening infections, viruses, and bacteria.
  • Disinfecting Water: Chlorine is often present in chemicals used to kill bacteria in drinking water and swimming pools. Chlorine is very effect against e coli bacteria.
  • Organic Chemistry: Chlorine has been found to be extremely useful for studying and synthesizing organic compounds (if these words are unfamiliar see 'What is Organic Chemistry ?' and 'What is a compound ?').
  • Oxidant: Chlorine is a powerful oxidant.
  • Pharmaceuticals: Chlorine chemistry is used in the production of a large proportional of all prescription drugs.
  • Swimming Pools: Chlorine is present in chemicals commonly used to keep swimming pools safe by killing potentially harmful bacteria that might otherwise thrive and multiply in the water, causing health hazards.

For more information about chlorine see the main page about chlorine element.

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