Chlorine was discovered by Carl Wilhelm Scheele in 1774. He erroneously believed that the substance contained oxygen. Later, in 1810, Humphry Davy named the substance chlorine and maintained that it was an element.
Precisely speaking, a greenish gas, chlorine directly combines with almost all the existing elements. Inhaling chlorine causes respiratory problems and, hence, it is known to be a respiratory irritant. Inside the respiratory tract, this gas causes irritation in the mucus membranes and the liquid form of chlorine burns the skin.
Chlorine belongs to the halogen series forming salts and it is hauled out from chlorides via electrolysis as well as oxidation.
In its pure form, this chemical element possesses the physical appearance of a diatomic gas. The name of the gas, chlorine, has been draw from the term "chloros", which denotes green and refers to its green color. Compared to air, chlorine is 2.5 times heavier and its odour is intensely offensive as well as suffocating. Chlorine can also be found in liquid and solid forms. In these two forms, the element is a potent disinfecting, bleaching and oxidizing agent.
The chemical element chlorine is widespread on the Earth's surface. However, it is never found in its pure form in the nature, because this element is extremely reactive and has a propensity to combine with other elements to form different compounds. When kept at normal pressure and room temperature, chlorine is yellowish-green gas, which is more than two times heavier compared to air. While a number of chlorine compounds are crucial for several forms of life, counting humans, it is highly toxic in its pure elemental form.
Chlorine has various industrial uses. In industries, this element is utilized for manufacture of plastics, pharmaceuticals and insecticides. In addition, chlorine is also used for disinfecting drinking water as well as water in swimming pools. In the paper industry, chlorine is used in the form of a bleaching agent.
Chlorine is element No. 17 in the periodic table. This is a group of elements that possess the same chemical properties as the halogens, which include elements like astatine, bromine, fluorine and iodine. Chlorine dissolves in water forming a hypochlorous solution and hydrochloric acids, while some of it remains as free chlorine. This gas is a very potent oxidizing agent. In other words, chlorine has an inclination to draw electrons from various other elements and form chemical compounds. Owing to this particular attribute of this gas, it easily blends with hydrogen as well as with several other metals to form various chlorides. Chlorine also readily combines with several organic compounds.
For industrial use, chlorine is mainly produced by means of electrolysis of common salt (sodium chloride) solutions. This process helps to separate the salt into its different elements. While the isolated sodium combines with water to form sodium hydroxide, chlorine is released in its gas form. In laboratories, this element can be produced in various different simple ways. For instance, chlorine can be produced by reacting acids with calcium hypochlorite or sodium. Alternatively, chlorine can also be produced by blending hydrochloric acid with potassium permanganate.
The food industry widely uses various different compounds of chlorine to disinfect foods and kill bacteria. Instances of use of chlorine compounds in food industry include washing vegetables and fruits, treating pasteurizer cooling water and sanitizing contact surfaces of foods.
Generally, chlorine is blended with inorganic compounds like calcium or sodium to produce hypochlorites. These compounds are very effectual as disinfectants. Chlorine combined with sodium is actually liquid bleach called sodium hypochlorite (NaOCl). Similarly, chlorine is generally combined with calcium in a tablet or granular form and is known as calcium hypochlorite (CaOCL). In addition, chlorine is also available in the form of chlorine dioxide (ClO2). Nevertheless, hypochlorites are considered to be the most active among all types of chlorine compounds.
Chlorine's oxidizing property makes it a highly effectual agent that kills harmful microbes. More than 25,000 people across the globe die every day from various water-borne diseases like typhoid and cholera. Chlorination of water is among the most extensively used means of sanitizing drinking water supplies. Chlorine that is added to water may be in its gaseous form or as hypochlorite compounds. These hypochlorite compounds may be both solutions in water or solids. Hypochlorites are slow releasing compounds. In other words, they release small amounts of chlorine into the water every time.
Even in very low concentrations chlorine is potent enough to kill majority of the pathogens. Normally, chlorine is mixed with water at the treatment plants. Even after the treatment, a very small amount of this element is left in the water to prevent water being contaminated during the course of its transportation to homes. There are some concerns regarding the potential effects of chlorine as well as its by-products present in the drinking water on the health of people using the water. However, as of now, there is no concrete that presence of such small amounts of the element in drinking water causes any harm. There is general consensus on the fact that the benefits of adding chlorine to drinking water are much more compared to the potential harms of chlorination.
When there was a major cholera outbreak in Latin America in 1991, many international health officials put the blame on the Peruvian government's decision to put an end to chlorination in a number of water supplies. This decision was taken following concerns raised by some people regarding the potential ill effects of chlorine in drinking water on the health of humans.
Although chlorination of drinking water may not be harmful for human health, tap water containing this element may be detrimental for the health of fish as well as a number of houseplants. However, chlorine can be removed from water by boiling it for some minutes or connecting a filter to your water supply. Alternatively, you can also get rid of chlorine from water by adding dechlorination tablets. Although this water may not be harmful for plants and fish, it is certainly not drinkable. You can use this water safely in fish tanks and for watering houseplants.
Aside from disinfecting foods and drinking water, chlorine is also added to water in swimming pools to sanitize it. As water in swimming pools is not meant for drinking, large amounts of chlorine may be added to it. Hence, when you are in a swimming pool you can get the distinctive smell of chlorine.
It is worth mentioning here that solutions made by adding chlorine to water, for instance household bleaches that are available commercially, are unstable compounds. In other words, chlorine may disperse very quickly, thereby decreasing its content as well as effectiveness. Therefore, it is advisable that chlorine powders are used in food processing plants instead of bottled bleach.
Several compounds containing chlorine are said to be responsible for causing damage to wildlife, ecosystems as well as the environment. For instance, chlorine compounds like chlorofluorocarbons (CFC), which were previously used as propellants and refrigerants, release chlorine gas when they reach the upper level of the atmosphere. The release of chlorine gas in the upper atmosphere leads to decomposition of ozone, causing damage to the ozone layer that works as a shield for life on Earth. Precisely speaking, the ozone layer protects all life forms on the Earth from exposure to excessive ultra-violet (UV) rays of the sun. Consequently, the use of such chemicals has been gradually stopped.
DDT, which contains chlorine, has been found to be harmful when it builds up in the food chain, especially its negative impact on birds of prey is concerning. As a result, DDT has been completely banned in the United States, while in other regions of the world this compound is banned for use in agriculture. Nevertheless, it is still used in some regions, especially to keep mosquitoes carrying malaria in check.
Chlorine as well as several compounds obtained from the element can be found in the lakes and rivers as result of waste water from pulp mills, other industries and even homes discharging chlorinated water or any other place using bleach. In case the amount of chlorine in the lakes and rivers is significantly high, it can prove to be detrimental for the health of aquatic life. It may even affect humans when the chemicals accumulate in the food chain. The government in the United States has established legal safety limits for adding chlorine to drinking water. The limit is 4 mg of the element in every litre of drinking water, while the safety limit for water in lakes and stream is 10 mg per litre.
Chlorine in its gaseous form may have adverse effects on the health of humans. However, this depends on the extent as well as the time for which an individual is exposed to chlorine gas. This greenish gas is acerbic as well as irritating to the skin, respiratory tract and the eyes. An individual exposed to low chlorine concentrations may suffer from coughing, eye and skin irritation and sore throat. However, when exposed to higher concentrations of chlorine, an individual may suffer from a burning sensation in the eyes, constriction of the bronchi and the color of the skin turning blue. Moreover, exposure to chlorine gas may also result in accumulation of fluids inside the lungs as well as cause chest pain.
Often, exposure to high intensity of chlorine gas may prove to be fatal. During the World War I, this gas was used in the form of a chemical weapon for causing mass deaths. However, such a situation is improbable in daily situations. On the other hand, household bleach, which contains chlorine, may prove to be dangerous if it is not handled carefully. Household bleach has the potential to exude large quantities of chlorine gas when it comes in contact with acids. Moreover, it also blends with products enclosing ammonia to produce poisonous chloramines.