Chlorine

Chlorine is one of 90 natural 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, and ensure a plentiful food supply.

Chlorine chemistry is deeply woven into the fabric of our lives.

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."
One of the most effective and economical germ-killers, chlorine also destroys and deactivates 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 1846, chlorine has been one of society's most potent weapons against a wide array of life-threatening infections, viruses, and bacteria for 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, chlorine 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 that have at least one atom of the element carbon in their molecular structure. 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 known elements, or substances, that consist of one type of atom. Elements cannot be reduced to simpler substances.

In this table, based on the pioneering work of the Russian scientist Dmitry Mendeleyev who published it in 1869, the elements are arranged in the order of their atomic number -- the number of protons in the nucleus of an atom of the 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. Each time you drive your car, drink a glass of water, wear vinyl rain gear, take vitamins or put on perfume, chlorine is working for you. 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.

Crop protection chemicals that depend on chlorine result in far higher crop yields -- thereby relieving pressures to convert to agricultural use rainforests and other ecologically important lands.

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.

A Closer Look

Here's a closer look at the automobile industry as just one example of how chlorine plays a central role -- and creates employment -- in so many modern industrial processes:

Automobiles rely on numerous components that contain chlorine or use chlorine during their manufacture. Three of the most important of these components are PVC parts for side molding, dashboards, air bags, restraints, and wiring; paint and protective coatings for the exterior finish of the car; and steel for the frame and undercarriage.

Let's look at PVC first. PVC resin is fabricated into finished PVC parts at 2,332 plants around the US, each of which employs an average of 54 workers.

The resin itself, however, must first be manufactured at one of 26 PVC resin plants in the US that employ, on average, 281 workers each.

The story follows a similar pattern when you look at steel. Thirty percent of the pickled steel manufactured in the US is used by the automobile industry. Pickled steel is produced at 50 factories around the country which employ an average of 2,660 workers each.

Hydrochloric acid plays a key part in the pickling process. In fact, 25% of all the hydrochloric acid manufactured in the US -- at 87 plants with about 680 employees each -- is used for steel pickling.

And once again chlorine shows up as an irreplaceable input in the manufacture of hydrochloric acid.

Paint is an essential part of car production, too. And most automobile paints and coatings use titanium dioxide, manufactured at 10 plants around the country that employ over 4,000 workers. And without chlorine, you can't make titanium dioxide.

In total, these three uses of chlorine in the automotive industry alone -- for PVC, pickled steel, and paint -- create more than 345,000 jobs in the US economy, as well as help sustain a total of 940,000 jobs in the auto industry as a whole.

Trade Surplus

The chemical industry is a significant competitor in world markets and enjoys a healthy net surplus in merchandise trade.
In 1990, the chemical industry as a whole had a net trade surplus of $16.5 billion. Chlorine-related products represented nearly 18 percent of that figure -- almost $2.9 billion.

Capital Investment

Gross private investment in chlorine-dependent industries in the US was estimated at $57 billion in 1990.

That's an amount equal to the cost of 400 brand new Boeing 747 jetliners.

Or total annual transportation outlays by the US government -- including outlays for mass transit, highway infrastructure, the federal railway system, airport construction and repair, and the Coast Guard.

Consumers

Due to its ability to combine and react with other elements and compounds, chlorine is a key chemical building block in manufacturing and a vital component in thousands of products we use everyday.
Virtually all US drinking water systems rely on chlorine and chlorine-based products for safe, cost effective disinfection.

Chlorine is used to produce 85 percent of our medicines and 96 percent of our crop protection chemicals.

A Common Building Block

Chlorine, oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium, hydrogen, phosphorous and carbon make up over 99 percent of the earth's crust, atmosphere and oceans (by weight). These elements are truly "building blocks" - they combine with other elements to form our world.

Chlorine Chemistry

Chlorine is commonly found in nature, but almost always in combination with other building blocks. Chlorine's structure makes it very reactive (its outer shell is missing just one electron), which makes it attractive to other atoms and molecules. Because it is so reactive, it is very useful to chemists, engineers and other people involved in making things we use every day. When combined with other chemical building blocks, chlorine can change the nature of a substance, and build or improve a product.

To be used in manufacturing, chlorine must first be separated from the other elements with which it is combined. Manufacturers use a process known as "electrolysis," which breaks down salt water into basic components, including chlorine. An electrical current passes through the salt water and splits apart the positive sodium and negative chloride ions. Since opposite charges attract, the negative chloride ions collect at the positive poles and form molecular chlorine gas. The gas is dried, chilled and pressurized, or converted to liquid for storage and shipping.

In other words:
Salt + Water (electricity)--------> Chlorine + Caustic Soda + Hydrogen
or:
2NaCL + 2H20 (electricity) --------> Cl2+ 2NaOH +H2


Using Chlorine


Where does chlorine go then? Into thousands of things you see and use every day. Every time you drink a glass of water, read a newspaper, put on a vinyl raincoat, brush your teeth or drive a car, you are using chlorine in some form.

Chlorine guards against diseases such as cholera, typhoid fever and dysentery in drinking water. Places like hospitals, households and swimming pools use chlorine-based compounds (such as bleach) for their disinfection needs. About 85 percent of the top-selling medicines are manufactured using chlorine chemistry. Chlorine also is used to manufacture versatile plastics such as vinyl (polyvinyl chloride). Crop-protection chemicals based on chlorine help feed the world and ward off insect-borne diseases. Chlorine helps ensure that products like disposable diapers and paper towels are strong and absorbent.

Chlorine also plays a role in the classroom. For example, it is used to make the vinyl and polyester in backpacks, is a critical component of computer chips, helps in the production of rubber for pencil erasers, and strengthens and brightens notebook paper.

Are All Chlorinated Compounds Alike?

Just because a chlorine molecule is attached to something does not make it the same as something else containing chlorine. For example, consider the following four salts. All contain chlorine, but they are not alike; each contains a different set of building blocks and offers unique characteristics.

Iron (ferric) chloride (FeCl3): Used to make pigments, inks and dyes, in controlling odors and removing phosphates from municipal waste water, in photographic processes, and as medicine.
Calcium chloride (CaCl2): Used (when in a water solution) as antifreezes and in refrigerating solutions, in preservation of wood and stone, in the manufacture of glues, cements and fireproof fabrics, and to speed the setting of concrete.
Sodium chloride (NaCl): Used in ceramic glazes, soap manufacturing, fire extinguishing solutions, and -- of course -- as table salt.
Cupric chloride (CuCl2): Used in wood preservation, in the fabric dyeing process, and, when mixed with other copper salts, as an agricultural fungicide.

Chlorine Through the Ages

The use of chlorine to disinfect water for drinking and swimming and its use in bleaching is fairly well known. However, it is not universally recognized that chlorine is an essential chemical building block, leading to a myriad of materials that are used to make the products we use every day. Chlorine chemistry is, for example, important to the production of pharmaceuticals, medical devices, safety equipment, computers, automobiles, aircraft parts and crop protection chemicals. The list is virtually endless.

Reference :
Web site http://c3.org

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