Chlorine
Discovered in 1774
by Carl
Wilhelm Scheele, who mistakenly thought it contained oxygen.
Chlorine was given its name in 1810
by Humphry
Davy, who insisted that it was in fact an element.
The pure chemical element has the physical form of a diatomic
green gas. The name chlorine is derived from chloros, meaning green,
referring to the color of the gas. Chlorine gas is two and one
half times as heavy as air, has an intensely disagreeable suffocating
odor, and is exceedingly poisonous. In its liquid and solid form it is a
powerful oxidizing, bleaching, and disinfecting agent.
This element is a part of the halogen series
forming salts. It is extracted from chlorides through oxidation
and electrolysis.
Chlorine gas is greenish-yellow and combines readily with nearly all
other elements.
Applications
Chlorine is an important
chemical in water
purification, in disinfectants,
in bleach
and in mustard
gas.
Chlorine is also used widely in the manufacture of many products and
items directly or indirectly, i.e.
in paper
product production, antiseptic, dyestuffs, food, insecticides, paints,
petroleum products, plastics, medicines, textiles, solvents, and many
other consumer products.
It is used to kill bacteria
and other microbes from drinking water supplies.
Chlorine is involved in beaching wood pulp for
paper making, bleach is also used industrially to remove ink from
recycle paper.
Chlorine often imparts many desired properties in an organic
compound when it is substituted for hydrogen
(synthetic
rubber), so it is widely use in organic chemistry, in the
production of chlorates, chloroform, carbon
tetrachloride, and in the bromine
extraction.
Chlorine in the environment
In nature it is only found
combined with other elements chiefly sodium
in the form of common
salt (NaCl), but also in carnallite,
and sylvite. Chlorides make up much of the salt dissolved in the earth's
oceans: about 1.9 % of the mass of seawater is chloride ions.
The amount of chloride in soils varies according to
the distance from the sea. The average in top soils is about 10 ppm.
Plants contain various amount of chlorine; it is an essential
microutrient for higher plants where is concentrates in the
chloroplasts. Growth suffers if the amount of chloride in the soil fall
below 2 ppm, but it rarely happens. The upper limit of tolerance
varies according to the crop.
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Chlorine is a highly reactive gas. It is a
naturally occurring element. The largest users of chlorine are
companies that make ethylene dichloride and other chlorinated
solvents, polyvinyl chloride (PVC) resins, chlorofluorocarbons,
and propylene oxide. Paper companies use chlorine to bleach paper.
Water and wastewater treatment plants use chlorine to reduce water
levels of microrganisms that can spread disease to humans
(disinfection).
Exposure to chlorine can occur in the workplace or in the
environment following releases to air, water, or land. People who
use laundry bleach and swimming pool chemicals containing chlorine
products are usually not exposed to chlorine itself. Chlorine is
generally found only in industrial settings.
Chlorine enters the body breathed in with contaminated air or when
consumed with contaminated food or water. It does not remain in
the body, due to its reactivity.
Effects of chlorine on human health depend on how the amount of
chlorine that is present, and the length and frequency of
exposure. Effects also depend on the health of a person or
condition of the environment when exposure occurs.
Breathing small amounts of chlorine for short periods of time
adversely affects the human respiratory system. Effects differ
from coughing and chest pain, to water retention in the lungs.
Chlorine irritates the skin, the eyes, and the respiratory system.
These effects are not likely to occur at levels of chlorine that
are normally found in the environment.
Human health effects associated with breathing or otherwise
consuming small amounts of chlorine over long periods of time are
not known. Some studies show that workers develop adverse effects
from repeat inhalation exposure to chlorine, but others will not.
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Chlorine dissolves when mixed with water. It
can also escape from water and enter air under certain conditions.
Most direct releases of chlorine to the environment are to air and
to surface water.
Once in air or in water, chlorine reacts with other chemicals. It
combines with inorganic material in water to form chloride salts,
and with organic material in water to form chlorinated organic
chemicals.
Because of its reactivity chlorine is not likely to move through
the ground and enter groundwater.
Plants and animals are not likely to store chlorine. However,
laboratory studies show that repeat exposure to chlorine in air
can affect the immune system, the blood, the heart, and the
respiratory system of animals.
Chlorine causes environmental harm at low levels. Chlorine is
especially harmful to organisms living in water and in soil.
More info about the effects
of gases such as chlorine in freshwater ecosystems
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Back to periodic
chart.
Recommended daily intake of
chlorine
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