The Element: Chlorine
General Information
We researched the chemical element known as chlorine. Chlorine has an atomic
number of 17 and an atomic weight of 35.453. It has a valence number of 3.
The element has 3 energy levels. Chlorine exists as a greenish-yellow gas at
normal temperatures and pressures. Chlorine is second in reactivity only to
fluorine among the halogen elements. Chlorine is a nonmetal. It is estimated
that 0.045% of the earth's crust and 1.9% of sea water are chlorine. Chlorine
combines with metals and nonmetals and organic materials to form hundreds of
chlorine compounds. Chlorine is about 2.5 times as dense as air and moderately
soluble in water, forming a pale yellowish green solution. Chlorine is so
reactive that it never occurs free in nature.
Chemical Properties
Chlorine is in the halogen family, and like all the other halogen elements
chlorine has a strong tendency to gain one electron and become a chloride ion.
Chlorine readily reacts with metals to form chlorides, most of which are
soluble in water. Chlorine also reacts directly with many nonmetals such as
sulfur, phosphorus, and other halogens. Chlorine can support combustion; if a
candle were to be thrown into a vessel of chlorine, it would continue to burn,
releasing dense, black clouds of smoke, The chlorine combines with hydrogen of
the paraffin, forming hydrogen chloride, and uncombined carbon is left in the
form of soot. Soot is black residue from fuel. Chlorine replaces iodine and
bromine from their salts. Dry chlorine is somewhat inert or not able to move,
but moist chlorine unites directly with most of the elements.
History
Chlorine was discovered in 1774 by Karl Scheele. Humphry Davy proved that
chlorine was an element. Extensive production began 100 years later. During
the 20th Century. The amount of Chlorine used was considered a measure of
industrial growth. In, 1975 chlorine productions ranked seventh on the list of
largest-volume chemicals produced in the United States. The importance of
chlorine has changed as new uses have been added. In 1925 paper and pulp
used over one-half . The chlorine made and chemical products only 10%. By the
1960's paper and pulp use accounted for only 15-17% and the chemical uses
increased to 75-80%. Peoples uses have contributed to the growth of large
cities, and new textiles, plastics, paints, and miscellaneous uses have raised
man's standard of living. Many large companies are based primarily on the
manufacture of chlorine and its compounds. In 1978 17% of the United States
production went into the production of vinyl chloride monomer. Other
chlorinated organics consumed 48% of United States Production.
Toxicity and Precautions
Chlorine was used in World War I as a poison gas. In fact most poisonous
gases have chlorine in them. Chlorine is very corrosive to moist tissue and
has a very irritating effect on the lungs and mucous membranes of the nose
and throat. Inhalation of chlorine gas can cause edema of the lungs and
respiratory stoppage. When hydrogen and chlorine gases are mixed together, the
mixture is stable if kept in a cool, dark place. If heated or exposed to
sunlight, the mixture explodes. Chlorine is easily liquefied and usually
transported in its liquid state in pressurized drums. Great care must be
taken, however, to prevent the containers from bursting and liberating large
amounts of the gas. In the United States most European countries, large
quantities of chlorine may only be transported by train. The present trend is
to limit the transport of chlorine as much as possible by producing and
using the element in the same location.
Uses
Chlorine has many great uses. Chlorine is an excellent oxidizing agent. At
first. The use of Chlorine was used as a bleaching agent in the paper,
pulp, and textile industries and as a germicide for drinking water preparation
swimming pool purification, and hospital sanitation has made community living
possible.
Chlorine is used in bleaching as said before. The bleaching action of
chlorine in aqueous solution is due to the formation of hypochlorous acid, a
powerful oxidizing agent. If a colored, oxidizable material is present,
hypochlorous acid releases its oxygen to oxidize the material to a colorless
compound. Liquid bleach is usually an aqueous solution of sodium hypochlorite,
and dry powder bleaches contain chloride of lime. Since chlorine destroys silk
and wool, commercial hypochlorite bleaches should never be used on these
fibers.
Chlorine is also used as a disinfectant. The oxidizing ability of chloride of
lime enables it to destroy bacteria; therefore large amounts are used to
treat municipal water systems. This chemical is also used in swimming pools
and for treating sewage.
Chlorine is used as rock salt. Sodium chloride, NaCl, is used directly as
mined (rock salt), or as found on the surface, or as brine also known as
salt water. It can be dissolved, purified, and reprecipated or given in
return for use in foods or when chemical purity is required. Its main uses
are in the production of soda ash and chlorine products. The form uses it
as refrigeration, dust, and ice control, food processing, and food
preservation. Calcium chloride, CaCl2, is usually obtained from salt water or
as a by product of chemical processing. Its main uses are road treatment,
coal treatment, and concrete conditioning.
In addition to these products, for which chlorine is needed, various other
chlorine compounds play an important part in chemistry and the chemical
industry. The chlorides of most metals are easily soluble in water, which
widens their applicability. Some other important compounds are the chlorates,
the perchlorates, and the hypochlorites. Hydrochloric acid is one of the most
frequently used acids.
Preparation
The most important method for preparation of chlorine is the electrolysis of
a solution of common salt, sodium chloride. The chlorine gas is liberated at
the positive anode or positively charged electrode, which is made of graphite
since a metal anode would react with chlorine. At the iron cathode or
negatively charged electrode, sodium ions are reduced to sodium metal, which
reacts immediately with water to form sodium hydroxide.
Another method of preparing chlorine is by the electrolysis of molten salt.
This process is used specifically to produce sodium, and the chlorine is a
commercial by product. When large quantities of waste hydrochloric and are
available. Chlorine may be recovered by oxidation of the acid. This method
has the advantage of converting great quantities of waste acid to useful
substances.
No matter what process is used to prepare chlorine, the gas must be well
dried. Dry chlorine is much less corrosive than moist chlorine gas. In the
laboratory chlorine may be prepared by heating manganese oxide with hydrochloric
acid.
Conclusion
In conclusion chlorine is a very wonderful element. Chlorine has hundreds of
compounds. If we did not have these compounds we would not have clean water,
we would have an insect problem, we could not make many important compounds
that are used in medicine, and some of the battles in World War I might
have been lost if it were not for chlorine. Our world would not be the
same if not for chlorine.
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