Chlorine is a reactive element that is commonly used in industry to produce plastics, insecticides, and pharmaceuticals, as well as to sanitize drinking water and swimming pools. It is also used in household bleach and disinfectants. While low concentrations of chlorine are effective in killing harmful microorganisms, high concentrations can be toxic and harmful to aquatic life. Chlorine gas can also have health effects, and household bleach can release toxic gases if handled improperly.
Chlorine is a common element on Earth, but it does not occur naturally in its pure state as it is very reactive and tends to form compounds with other elements. At room temperature and normal pressure, it is a yellow-green gas heavier than air. Although some of its compounds are essential to many life forms, including humans, in its elemental form, the gas is very toxic. Chlorine is used industrially to produce plastics, insecticides and pharmaceuticals; to sanitize drinking water and in swimming pools; and as a bleaching agent in the paper industry.
Property
Element number 17 on the periodic table, chlorine is one of a group of elements that share similar chemical properties known as halogens, with the other members being fluorine, bromine, iodine and astatine. The gas dissolves in water, forming a mixture of hypochlorous and hydrochloric acids and free chlorine. It is a strong oxidizing agent, which means it tends to capture electrons from other elements to form compounds. It combines easily in this way with hydrogen and with metals to form chlorides, as well as combines easily with many organic compounds.
Production
This element is produced industrially mainly by the electrolysis of common salt (sodium chloride) solutions. The process breaks down the salt into its elements, with the sodium combining with water to form sodium hydroxide and the chlorine produced as a gas. There are several simple ways to produce the element in the laboratory, such as by the action of acids on sodium or calcium hypochlorite or by mixing hydrochloric acid and potassium permanganate.
it is used
The oxidizing properties of this element make it very effective in killing harmful microorganisms. Over 25,000 people worldwide die every day from waterborne diseases, such as cholera and typhoid. Chlorination of water is one of the most widely used safeguards for the drinking water supply. Chlorine can be added to water as a gas or in the form of hypochlorite compounds, which can be solids or solutions in water. Hypochlorites release small amounts of the element into the water.
Very low concentrations of chlorine are sufficient to kill most disease-causing organisms. Although it is normally added in water treatment plants, very small amounts can remain in the water in case it becomes contaminated on its way to homes. Some concerns have been expressed about the possible health effects of this element and its byproducts in drinking water, but there is no conclusive evidence that it is harmful. The consensus is that the benefits of water chlorination far outweigh the risks. In 1991, a major cholera outbreak in Latin America was blamed by international health officials on a Peruvian government decision to stop chlorinating some water supplies in response to concerns about its effects on human health.
The chlorine in tap water can be harmful to fish and some houseplants, but it can be removed by boiling the water for a few minutes or by attaching a filter to the tap. Another method is to add dechlorination tablets. This makes the water undrinkable, but it is suitable for filling aquariums.
The element is also used to disinfect swimming pools. As the water is not potable, larger quantities may be used and the odor may be quite noticeable.
Chlorine is also used in the following ways:
In pharmaceuticals, including important antibiotics and antimalarial drugs;
To produce insecticides, such as dichlorodiphenyltrichloroethane (DDT);
As part of some plastics, such as polyvinyl chloride (PVC);
For bleaching paper in paper mills;
In household bleach and disinfectants.
Environmental concerns
Many chlorine compounds have been implicated in damage to ecosystems, wildlife and the environment. Chlorofluorocarbons (CFCs) — formerly used as refrigerants and propellants — release chlorine gas when they reach the upper atmosphere. This decomposes ozone, damaging the ozone layer that protects life on Earth from excessive exposure to ultraviolet radiation. As a result, the use of these compounds has been phased out.
Concerns about the accumulation of DDT in the food chain and, in particular, its effects on birds of prey, have led to a blanket ban in the United States and a worldwide ban on agricultural use. However, it is still used in some areas to control malaria-carrying mosquitoes.
Chlorine and compounds derived from it can find their way into rivers and lakes through wastewater from pulp mills and homes with chlorinated water or where bleach has been used. If present in sufficient quantities, it can be harmful to aquatic life, either directly or by accumulation of its compounds in the food chain. In the United States, the government has set safe legal limits of 4 milligrams of chlorine per gallon of drinking water and 10 milligrams per gallon of lakes and streams.
Health and safety issues
Chlorine gas can have health effects, depending on the level and duration of exposure. It is corrosive and irritant to eyes, skin and respiratory tract. Exposure to low concentrations may cause sore throat, eye and skin irritation, and coughing. At higher concentrations, the gas can cause bronchial narrowing, burning eyes and blue discolouration of the skin. It can also cause a buildup of fluid in the lungs and chest pain.
Exposure to high concentrations of the gas can quickly be fatal – it was used as a chemical weapon during World War I – but is unlikely in everyday situations. However, household bleach can be dangerous if handled improperly. It can release large quantities of gas on contact with acids and combines with ammonia-containing products to form toxic chloramines.
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