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
Chlorine + Caustic Soda + Hydrogen


2NaCL + 2H20
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.


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