What is greenish-yellow, is a gas at room temperature, is heavier than air and has a pungent smell? If you guessed element number 17 or chlorine you are absolutely correct. When Swedish pharmacist, Carl Wilhem Scheele, dropped hydrochloric acid onto manganese dioxide and discovered the greenish-yellow gas (1774), he was unaware of the impact his discovery would have on society. In fact, he and many other scientists thought the gas was an oxide therefore they were trying to remove the oxygen from it. It was not until thirty-six years later that Sir Humphrey Davey identified chlorine as an element and named it khloros which is greek for "greenish-yellow." (CCC 1998)
Chlorine is a highly reactive halogen that exists in nature usually bound to sodium, potassium or
magnesium atoms (CCC 1998, Petrucci 1993). The diatomic molecule (Cl2) melts at 103C (276
K) and boils at -34C (239 K) (CCC 1998). The production of chlorine is a multimillion dollar
industry, producing twelve million tons of chlorine in North America each year (CCC 1998).
Eleven million tons of the chlorine produced comes from salt (Brady 198 1). Chlorine is isolated
from the environment by allowing sea water to flow into low-lying areas called salt pans. Here the
water evaporates, sand and clay settles and the concentrated salt solution flows into crystallizing
pans where the salt is extracted from the water. Pure rock salt is also mined. The most common
method of making chlorine is to pass electric current through molten NaCl (salt). This process,
called electrolysis, separates the NaCl into the following products. (Brady 1981, CCC 1998, The
Vinyl Institute 1998)
Most North Americans take their tap water for granted. The reality is that since the introduction of chlorine into the water systems in 1908, cholera, dysentery and other waterborne illnesses have been almost eradicated (CCC 1998). In comparison, third world countries who do not have chlorinated water systems have ever increasing rates of disease and mortality due to waterborne bacteria. Chlorine's ability to destroy the outer surfaces of bacteria and viruses give it unique disinfectant properties. In 1846, chlorine was first used as a germicide to stop the spread of child bed fever in an Austrian hospital. Since then, chlorine disinfectants have virtually eliminated typhoid fever. Restaurants, meat packing industries, hospitals, grocery stores and households rely on chlorine containing decontamination products to eliminate bacteria and prevent disease. Dissolving chlorine in water results in the formation of partial bonds between the chlorine atoms and the water molecules. These are then called hypochlorites, better known as household bleach. Hypochlorites have the ability to turn coloured substances white as well as to disinfect. (CCC 1998, Asimov 1974)
Chlorine has several major uses in society. Thirty-five percent of all the chlorine produced is used to make pharmaceuticals such as those which treat hypertension and Alzheimers disease (CCC 1998). Twenty-five percent of all of the chlorine produced is used to make polyvinyl chloride (PVC) (CCC 1998). PVC is formed by combining pure chlorine and ethylene (obtained by cracking natural gas). The result is ethylene dichloride which is then used to make PVC compounds. PVC is used to make a variety of products from vinyl siding to gaskets to inflatable rafts to insulation to plastic wrap, which are just a few examples from a list too numerous to mention. (The Vinyl Institute 1998)
One of the main components of most pesticides is chlorine. Their effect on insects can be illustrated in the following limerick.
The pesticide described in this limerick is better known as DDT. DDT has had a huge impact on food production and in preventing outbreaks of malaria. Although now banned from use, DDT was used to control mosquito populations and terminate the spread of cholera during World War II. Some other uses of chlorine or chlorine products are to produce metal working and dry cleaning solvents, wood preservants and in pulp and paper bleaching. (Capindale 1984, CCC 1998, NRCC 1982)
Chlorine has many uses and is extremely important to the survival of the human race. For 152
years chlorine's chemical properties have been utilized to make the world a more comfortable and
safer place to live. Used in water purification, crop protection, pharmaceuticals and disinfectants,
chlorine really is the life-saving element!
Return to the Gallery.
Return to the Home Page.
End of file.