Chlorine Chemistry

Chlorine is one of approximately 100 natural chemical elements, the basic building blocks of our planet.

To be useful, an element must be relatively abundant or have extremely desirable properties. Chlorine has both characteristics.

As a result—over the course of many decades of careful research and development—scientists have learned to use chlorine and the products of chlorine chemistry to make drinking water safe, destroy life-threatening germs, produce life-saving drugs and medical equipment, shield police and fire fighters in the line of duty, ensure a plentiful food supply and more.

The Discovery

In 1774, in his small experimental laboratory, Swedish pharmacist Carl Wilhem Scheele released a few drops of hydrochloric acid onto a piece of manganese dioxide. Within seconds, a greenish-yellow gas arose.

Although he had no idea at the time, he had just discovered chlorine.

The fact that the greenish-yellow gas was actually an element was only recognized several decades later by English chemist Sir Humphrey Davy. Until that time, people were convinced that the gas was a compound of oxygen. Davy gave the element its name on the basis of the Greek word khloros, for greenish-yellow. In 1810 he suggested the name "chloric gas" or "chlorine."

Some of the most effective and economical germ-killers, chlorine disinfectants destroy and deactivate a wide range of dangerous germs in homes, hospitals, swimming pools, hotels, restaurants, and other public places.

Chlorine's powerful disinfectant qualities come from its ability to bond with and destroy the outer surfaces of bacteria and viruses.

First used as a germicide to prevent the spread of "child bed fever" in the maternity wards of Vienna General Hospital in Austria in 1847, chlorine has been one of society's most potent weapons against a wide array of life-threatening infections, viruses, and bacteria for over 150 years.

Disinfectant Qualities

Restaurants and meat and poultry processing plants rely on chlorine bleach and other chlorine-based products to kill harmful levels of bacteria such as Salmonella and E. coli on food preparation surfaces and during food processing.

Chlorine is so important in poultry processing that the US Department of Agriculture requires an almost constant chlorine rinse for much of the cutting equipment. In fact, no proven economical alternative to chlorine disinfection exists for use in meat and poultry processing facilities.

Properties

Because it is highly reactive, chlorine is usually found in nature bound with other elements like sodium, potassium, and magnesium. When chlorine is isolated as a free element, it is a greenish yellow gas, which is 2.5 times heavier than air. It turns to a liquid state at -34°C (-29°F), and it becomes a yellowish crystalline solid at -103°C (-153°F).

Chemists began experimenting with chlorine and chlorine compounds in the 18th century. They learned that chlorine has an extraordinary ability to extend a chemical bridge between various elements and compounds that would not otherwise react with each other.

Chlorine has been especially useful in studying and synthesizing organic compounds—compounds of mostly carbon and hydrogen. All living organisms, including humans, are composed of organic compounds.

The periodic table is the single most unifying concept in chemistry. It is a structured listing of all the known chemical elements. Elements cannot readily be reduced to simpler substances. In this table, based on the pioneering work of the Russian scientist Dimitri Ivanovich Mendelev who published it in 1869, the elements are arranged in the order of their atomic number—equal to the number of protons in the nucleus of each atom of a given element.

The horizontal rows of the table are called periods. All elements in a period have the same number of layers, or shells, of electrons.

The table's vertical columns are called groups. Elements that occupy one group all have the same number of electrons in their outermost shell. Elements of any particular group tend to have similar chemical properties.

Environment

Chlorine opens doors to thousands of social and public health benefits. If you drive a car, use a computer, drink a glass of water, or wear vinyl rain gear, chlorine is working for you. Chlorine chemistry is also used to produce 93 percent of all prescription drugs used in the U.S. Some people are surprised to learn that chlorine works for the environment, too.

Chlorine is an important component in the development and manufacture of materials that make vehicles lighter—thereby increasing gasoline mileage.

Using crop protection chemicals that depend on chlorine results in high crop yields—thereby relieving pressures to convert rainforests and other ecologically important lands to agricultural use.

Chlorine even plays an important role in harnessing solar energy—purifying the silicon found in grains of sand and helping transform them into solar panel chips.

In so many ways, chlorine is part of the bedrock of sustainable development efforts and other central tenets of modern environmental protection.

Human Body

Without sodium chloride (salt), there would be no life. Life began in the ocean, a largest repository of salt which is derived from the weathering of the continents.

Sodium chloride literally keeps our bodies from drying up, moves our muscles, makes our meals matter, and attacks germs to keep us healthy.

Our body's cells exist in a sea of fluid. This extracellular body fluid is mostly water, along with the charged atoms (ions) of sodium and chloride. Chloride plays an essential role in a delicate balancing act: providing for the electrical neutrality and the correct pressure of body fluids, and keeping the acid-base balance of the body.

One result of this balancing act is that the amount of water we retain and concentrations of salt in our bodies remain relatively constant over time. We don't dry up nor do we bloat uncontrollably. When changes occur, the balance reasserts itself. For example, after heavy exercise and perspiration the body requires salt; and we are usually thirsty after eating salty food.

Human Body: Muscles

Sodium ions play an important role in our body's communication system. The nimbleness of a world class pianist or the dexterity of an Olympian athlete depend on the inner working of the central nervous system. Sodium ions are vital to the transmission of impulses from our brains to our muscles through the complex network of nerve cells.

On the flip side are the chloride ions, which assist in balancing the electrical charges throughout our nervous system.

Human Body: Digestive System

Chloride ions are building blocks of hydrochloric acid, which is essential to our digestive system. Hydrochloric acid made in the stomach has two main purposes: to help destroy germs that arrived with the food; and to help pepsin, an enzyme, break down the proteins found in the food stuffs, ensuring that essential nutrients are made available to the body.

Human Body: Immune System

In the immune system, which is charged with fighting off the daily invasion of germs, chlorine is there to lend a hand. When infections take place, hypochlorite—a chlorine-containing compound which is a well-known disinfectant—forms in white blood cells. Hypochlorite itself attacks the germs, or helps to activate other agents that do the work.

Everyday Life

Probably the most familiar everyday use of chlorine is table salt, or sodium chloride. But as one of the major "building blocks" of industrial production, nearly all manufactured products benefit in some way from chlorine.

From the ground up, many homes are constructed and decorated with chlorine-related products like concrete, house paint, fiberglass insulation, and nylon carpeting, as well as vinyl siding, windows, plumbing pipes, and floor tiles.

Chlorine helps make automobiles safer, more efficient, and more comfortable as a component in the manufacture of seat belts, air bags, upholstery, bumpers, floor mats, dashboards and other plastic items, fan and alternator belts, hoses, gaskets, seals, gasoline additives, brake and transmission fluids, anti-freeze, and air conditioning systems.

The modern-day office depends on chlorine for many electronic devices, such as microprocessors, telephones and computer disks, and plastic housings for computers and keyboards.

Even recreational activities depend on chlorine chemistry. Vinyl soccer balls, golf bags, nylon tents and water-proof jackets, wet suits and inflatable rafts, surfboards, tennis rackets, football helmets, and hundreds of toys are just a few of the items that need chlorine for their manufacture.

The most common method of making chlorine is by passing an electric current through a saltwater solution. The solution separates into chlorine and two other useful products: sodium hydroxide—also known as caustic soda or lye—and hydrogen.

Every year, approximately 13.6 million metric tons of chlorine are produced in North America.

The greatest volume of North American chlorine, about 40 percent, is used in the production of polyvinyl chloride, PVC, a low-cost, versatile plastic used to construct everything from water pipes and home siding to appliance parts and food storage containers. About 37 percent of chlorine produced in North America is used to produce other organic compounds, including basic chemicals needed for manufacturing, and solvents for metalworking, dry cleaning, and electronics. Roughly 4 percent of North American chlorine is used for water treatment. Other inorganic uses of chlorine include producing hydrochloric acid for myriad chemical processes and titanium dioxide, a popular white pigment.

In countless industrial processes, there's simply no cost-effective, safe substitute for chlorinated compounds.