Chlorine is one of the most active of all elements. It combines with all elements except the noble gases of Group 18 of the periodic table. Chlorine does not undergo combustion, although it does support combustion in much the same way as does oxygen. This module highlights the importance of chlorine.

1. CHLORINE & ITSCHLORINE & ITS
IMPORTANCEIMPORTANCE
BYBY
PROF. A. BALASUBRAMANIANPROF. A. BALASUBRAMANIAN
CENTRE FOR ADVANCED STUDIES IN EARTHCENTRE FOR ADVANCED STUDIES IN EARTH
SCIENCESCIENCE
UNIVERSITY OF MYSORE, INDIAUNIVERSITY OF MYSORE, INDIA

2. CHLORINECHLORINE
 Number 17 on the "periodicNumber 17 on the "periodic
table" of elementstable" of elements
 Chlorine is found in soils,Chlorine is found in soils,
minerals, plants and animals.minerals, plants and animals.
 Chlorine occurs commonly both
in the Earth's crust and in
seawater.
 Its abundance in the earth is
about 100 to 300 parts per
million.

3.  It ranks 20th among the
elements in abundance in the
earth.
 Seawater is a huge reservoirSeawater is a huge reservoir
of dissolved chlorineof dissolved chlorine
weathered from theweathered from the
continents and transported tocontinents and transported to
the oceans by Earth's rivers.the oceans by Earth's rivers.
 Its abundance in seawater is
about 2 percent.

4.  Chlorine compounds haveChlorine compounds have
been important to humans forbeen important to humans for
thousands of years.thousands of years.
 Ordinary table salt, forOrdinary table salt, for
example, is sodium chlorideexample, is sodium chloride
(NaCl).(NaCl).
 Until 1774 , chlorine was notUntil 1774 , chlorine was not
recognized as an element,recognized as an element,
when Scheele was studyingwhen Scheele was studying
the mineral pyrolusite.the mineral pyrolusite.

5.  Chlorine is the second element inChlorine is the second element in
Group 17 of theGroup 17 of the periodic tableperiodic table , a, a
group of elements known as thegroup of elements known as the
halogenshalogens..
 Halogens are a highly reactive group ofHalogens are a highly reactive group of
elements that, in addition to chlorine,elements that, in addition to chlorine,
include fluorine, iodine,include fluorine, iodine, brominebromine andand
another element that does not occur inanother element that does not occur in
naturenature, astatine, astatine
 Chlorine'sChlorine's atomic numberatomic number is 17,is 17,
 its atomicits atomic massmass is 35.453, andis 35.453, and
 its chemical symbol is Cl.its chemical symbol is Cl.

6.  chlorine is usually not found inchlorine is usually not found in
a pure form in nature,a pure form in nature,
 but is rather typically bound tobut is rather typically bound to
other elements such asother elements such as
sodium, calcium, orsodium, calcium, or
potassium.potassium.
 In its pure form, chlorineIn its pure form, chlorine
exists as a diatomic moleculeexists as a diatomic molecule

7.  Because of its reactivity,Because of its reactivity,
desirable properties, anddesirable properties, and
abundance, chlorine is anabundance, chlorine is an
exceptionally useful element.exceptionally useful element.
 Since it readily combines withSince it readily combines with
other elements and molecules, itother elements and molecules, it
is a main component and vitalis a main component and vital
reactant in the manufacture ofreactant in the manufacture of
thousands of other usefulthousands of other useful
products.products.

8.  Chlorine is a greenish yellow
poisonous gas with a density of
3.21 grams per liter.
 Its specific gravity compared to
air is 2.49.
 Chlorine's boiling point is
-29.29°F (-34.05°C) and
 its melting point is -149.8°F (-
101°C).
 The gas is soluble in water and
reacts with water as it dissolves.

9.  Chlorine is one of the mostChlorine is one of the most
active of all elements.active of all elements.
 It combines with all elementsIt combines with all elements
except the nobleexcept the noble gasesgases ofof
Group 18 of the periodic table.Group 18 of the periodic table.
 Chlorine does not undergoChlorine does not undergo
combustioncombustion , although it does, although it does
support combustion in muchsupport combustion in much
the same way as doesthe same way as does
oxygenoxygen..

10. BIOGEOCHEMICAL CYCLES OFBIOGEOCHEMICAL CYCLES OF
ELEMENTSELEMENTS
 The chemical elements present in theThe chemical elements present in the
lithosphere or hydrosphere enter into thelithosphere or hydrosphere enter into the
biosphere through food chains. Later they arebiosphere through food chains. Later they are
ejected out from the organisms as productsejected out from the organisms as products
of metabolism or left in to the ecosystemsof metabolism or left in to the ecosystems
after death.after death.
 These elements will again enter into theThese elements will again enter into the
biosphere through another organism. Thebiosphere through another organism. The
movement of these elements continue, likemovement of these elements continue, like
this.this.
 This continuous circulation of elementsThis continuous circulation of elements
among the earth's environmental segments isamong the earth's environmental segments is
called as the biogeochemical cycles.called as the biogeochemical cycles.

11.  The transport and transformationThe transport and transformation
of substances in the environment,of substances in the environment,
through life, air, sea, land, andthrough life, air, sea, land, and
ice, are known collectively asice, are known collectively as
biogeochemical cycles.biogeochemical cycles.
 These are global cycles as theyThese are global cycles as they
move through all the spheres ofmove through all the spheres of
the globe.the globe.

12.  Within the bodies of living organisms,Within the bodies of living organisms,
many chemical reactions can occurmany chemical reactions can occur
even at low temperature.even at low temperature.
 These reactions take place mainly dueThese reactions take place mainly due
to the enzymic action.to the enzymic action.
 An example is the nitrogen fixing microAn example is the nitrogen fixing micro
organisms.organisms.
 The mass of living matter in biosphereThe mass of living matter in biosphere
is very little when compared to theis very little when compared to the
other spheres.other spheres.
 However, biosphere has a greatHowever, biosphere has a great
geochemical significance andgeochemical significance and
influence.influence.

13.  Though chlorine is not a nutrient,Though chlorine is not a nutrient,
its role in the environment is aits role in the environment is a
significant one.significant one.
 It also circulates along with otherIt also circulates along with other
elements in nature.elements in nature.
 It is an environmentallyIt is an environmentally
significant element for humansignificant element for human
understanding.understanding.
 In this episode, the details ofIn this episode, the details of
chlorine and the environment arechlorine and the environment are
discussed.discussed.

14. Occurrence andOccurrence and
ExtractionExtraction
 Chlorine occurs abundantly in theChlorine occurs abundantly in the
Earth's crust and in the Earth'sEarth's crust and in the Earth's
hydrosphere.hydrosphere.
 Its abundance in the earth is aboutIts abundance in the earth is about
100-300 parts per million, making it100-300 parts per million, making it
about the 20th most abundant elementabout the 20th most abundant element
in the crust.in the crust.
 Its abundance in seawater is about 2%,Its abundance in seawater is about 2%,
where it occurs primarily aswhere it occurs primarily as sodiumsodium
chloride (NaCl) andchloride (NaCl) and potassiumpotassium
chloride (KCl).chloride (KCl).

15.  The most common minerals ofThe most common minerals of
chlorine are halite, or rockchlorine are halite, or rock saltsalt
(NaCl), sylvite (KCl), and(NaCl), sylvite (KCl), and
carnallite (KClMgCl2).carnallite (KClMgCl2).
 Large amounts of these mineralsLarge amounts of these minerals
are mined from underground saltare mined from underground salt
beds that were formed whenbeds that were formed when
ancient oceans dried up.ancient oceans dried up.

16. Discovery and NamingDiscovery and Naming
 Chlorine was discovered by the SwedishChlorine was discovered by the Swedish
chemistchemist Carl Wilhelm ScheeleCarl Wilhelm Scheele ..
 Scheele produced chlorine by treating theScheele produced chlorine by treating the
mineral pyrolusite (primarilymineral pyrolusite (primarily manganesemanganese
dioxide, MnO2) withdioxide, MnO2) with hydrochloric acidhydrochloric acid (HCl).(HCl).
 Scheele described the chlorine gas formed asScheele described the chlorine gas formed as
having a greenish yellowhaving a greenish yellow colorcolor and aand a
suffocating odor "most oppressive to thesuffocating odor "most oppressive to the
lungs."lungs."
 The true nature of the gas as an element wasThe true nature of the gas as an element was
described in 1807 by the English chemist anddescribed in 1807 by the English chemist and
physicistphysicist Humphry DavyHumphry Davy ..
 Davy suggested the name chlorine for the gasDavy suggested the name chlorine for the gas
based on the Greek word chloros meaningbased on the Greek word chloros meaning
"greenish yellow.""greenish yellow."

17.  Chlorine is producedChlorine is produced
industrially from theindustrially from the
compound sodium chloride.compound sodium chloride.
 When electricity is appliedWhen electricity is applied
to a brine solution of sodiumto a brine solution of sodium
chloride, chlorine gas (Cl2),chloride, chlorine gas (Cl2),
caustic soda (NaOH) andcaustic soda (NaOH) and
hydrogen gas (H2) arehydrogen gas (H2) are
generated according to thegenerated according to the
following reaction:following reaction:
Salt + Water ---> ChlorineSalt + Water ---> Chlorine
Gas + Caustic Soda +Gas + Caustic Soda +

18.  Chlorine is one of the basicChlorine is one of the basic
builidng blocks of our planet.builidng blocks of our planet.
 Chlorine is usually found inChlorine is usually found in
nature bound with othernature bound with other
elements like sodium,elements like sodium,
potassium, and magnesium.potassium, and magnesium.
 When chlorine is isolated as aWhen chlorine is isolated as a
free element, chlorine is afree element, chlorine is a
greenish yellow gas, which isgreenish yellow gas, which is
2.5 times heavier than air.2.5 times heavier than air.

19.  It turns to a liquid state atIt turns to a liquid state at
-34°C (-29°F), and it-34°C (-29°F), and it
becomes a yellowishbecomes a yellowish
crystalline solid at -103°Ccrystalline solid at -103°C
(-153°F).(-153°F).
 In nature it is found in theIn nature it is found in the
combined state only,combined state only,
chiefly with sodium aschiefly with sodium as
common salt (NaCl),common salt (NaCl),
carnallite, and sylvitecarnallite, and sylvite

20.  Chlorine is one of theChlorine is one of the
most effective andmost effective and
economical germ-economical germ-
killers.killers.
 It destroys andIt destroys and
deactivates a widedeactivates a wide
range of dangerousrange of dangerous
germs in homes,germs in homes,
hospitals, swimminghospitals, swimming
pools, hotels,pools, hotels,

21. Chlorine's powerfulChlorine's powerful
disinfectant qualities comedisinfectant qualities come
from its ability to bond withfrom its ability to bond with
and destroy the outerand destroy the outer
surfaces of bacteria andsurfaces of bacteria and
viruses.viruses.

22.  It was first used as aIt was first used as a
germicide to prevent thegermicide to prevent the
spread of "child bed fever"spread of "child bed fever"
in the maternity wards ofin the maternity wards of
Vienna General Hospital inVienna General Hospital in
Austria in 1846.Austria in 1846.
 Chlorine has been one ofChlorine has been one of
society's most potentsociety's most potent
weapons against a wideweapons against a wide
array of life-threateningarray of life-threatening
infections, viruses, andinfections, viruses, and
bacteria for 150 years.bacteria for 150 years.

23.  Without sodium chlorideWithout sodium chloride
(salt), there would be no(salt), there would be no
life.life.
 Life began in the ocean,Life began in the ocean,
the largest source of saltthe largest source of salt
and the origin of alland the origin of all
organic material.organic material.
 Through evolution, ourThrough evolution, our
bodies learned how to usebodies learned how to use
salt, and its constituentsalt, and its constituent
elements such aselements such as

24.  Sodium chloride literallySodium chloride literally
 keeps our bodies fromkeeps our bodies from
drying up,drying up,
 moves our muscles,moves our muscles,
 makes our meals matter,makes our meals matter,
andand
 attacks germs to keep usattacks germs to keep us
healthy.healthy.
 The average human body
contains about 95 grams
(about 3.5 ounces) of

25.  Our body's cells exist in a sea ofOur body's cells exist in a sea of
fluid.fluid.
 This extra-cellular body fluid isThis extra-cellular body fluid is
mostly water, along with themostly water, along with the
charged atoms (ions) of sodiumcharged atoms (ions) of sodium
and chloride.and chloride.
 Chloride and other chlorineChloride and other chlorine
compounds play an essential rolecompounds play an essential role
in a delicate balancing act:in a delicate balancing act:
 providing for the electricalproviding for the electrical
neutrality andneutrality and
 the correct pressure for the bodythe correct pressure for the body
fluids, andfluids, and
 in keeping the acid-base balancein keeping the acid-base balance
of the body.of the body.

26.  One result of this balancing act isOne result of this balancing act is
that the amount of water andthat the amount of water and
concentrations of the salt remainconcentrations of the salt remain
relatively constant over time.relatively constant over time.
 We don't dry up nor do we bloatWe don't dry up nor do we bloat
uncontrollably.uncontrollably.
 When changes occur, the balanceWhen changes occur, the balance
reasserts itself.reasserts itself.
 For example, after heavy exerciseFor example, after heavy exercise
the body requires salt; andthe body requires salt; and
 we are usually thirsty after eatingwe are usually thirsty after eating
salty food.salty food.

27.  Chloride ions are building blocksChloride ions are building blocks
of hydrochloric acid, which isof hydrochloric acid, which is
essential to our digestive system.essential to our digestive system.
 Hydrochloric acid made in theHydrochloric acid made in the
stomach has two main purposes:stomach has two main purposes:
 to help destroy germs that arrivedto help destroy germs that arrived
with the food; andwith the food; and
 to help pepsin, an enzyme, breakto help pepsin, an enzyme, break
down the proteins found in thedown the proteins found in the
food stuffs, ensuring thatfood stuffs, ensuring that
essential nutrients are madeessential nutrients are made
avail- able to the body.avail- able to the body.

28.  Chlorine in water reactsChlorine in water reacts
with living tissues andwith living tissues and
organic matter causingorganic matter causing
acute necrosis (cellacute necrosis (cell
death) in fish.death) in fish.
 Most municipal waterMost municipal water
companies sterilize theircompanies sterilize their
water with chlorine orwater with chlorine or
chloramine, a combinationchloramine, a combination
of chlorine and ammonia,of chlorine and ammonia,
for safe humanfor safe human

29.  While relatively harmlessWhile relatively harmless
to humans, chlorine canto humans, chlorine can
be deadly to fish.be deadly to fish.
 The amount of chlorine inThe amount of chlorine in
tap water may fluctuate,tap water may fluctuate,
but it is usually betweenbut it is usually between
0.5 and 2.0 parts per0.5 and 2.0 parts per
million (ppm).million (ppm).

30. Chlorine ToxicityChlorine Toxicity
 Chlorine is a greenish-Chlorine is a greenish-
yellow, noncombustible gasyellow, noncombustible gas
at room temperature andat room temperature and
atmospheric pressure.atmospheric pressure.
 The intermediate waterThe intermediate water
solubility of chlorinesolubility of chlorine
accounts for its effect onaccounts for its effect on
the upper airway and thethe upper airway and the
lower respiratory tract.lower respiratory tract.

31.  Exposure to chlorine gasExposure to chlorine gas
may be prolonged becausemay be prolonged because
its moderate waterits moderate water
solubility may not causesolubility may not cause
upper airway symptomsupper airway symptoms
for several minutes.for several minutes.
 In addition, the density ofIn addition, the density of
the gas is greater thanthe gas is greater than
that of air, causing it tothat of air, causing it to
remain near ground levelremain near ground level
and increasing exposureand increasing exposure

32.  The odor threshold forThe odor threshold for
chlorine ischlorine is
approximately 0.3-0.5approximately 0.3-0.5
parts per million (ppm);parts per million (ppm);
 however, distinguishinghowever, distinguishing
toxic air levels fromtoxic air levels from
permissible air levelspermissible air levels
may be difficult untilmay be difficult until
irritative symptoms areirritative symptoms are
present.present.

33.  Chlorine gas is a pulmonaryChlorine gas is a pulmonary
irritant with intermediateirritant with intermediate
water solubility that causeswater solubility that causes
acute damage in the upperacute damage in the upper
and lower respiratory tract.and lower respiratory tract.
 Elemental chlorine and itsElemental chlorine and its
derivatives, hydrochloric andderivatives, hydrochloric and
hypochlorous acids, mayhypochlorous acids, may
cause biological injury.cause biological injury.

34.  Chlorinated water is aChlorinated water is a
skin irritant and it can beskin irritant and it can be
associated with rashesassociated with rashes
like eczema.like eczema.
 Chlorinated water canChlorinated water can
destroy polyunsaturateddestroy polyunsaturated
fatty acids and vitamin Efatty acids and vitamin E
in the body whilein the body while
generating toxins capablegenerating toxins capable
of free radical damageof free radical damage
(oxidation).(oxidation).

35.  Chlorinated waterChlorinated water
destroys much of thedestroys much of the
intestinal flora, theintestinal flora, the
friendly bacteria thatfriendly bacteria that
help in the digestion ofhelp in the digestion of
food and which protectfood and which protect
the body from harmfulthe body from harmful
pathogens.pathogens.

36.  Chlorinated water containsChlorinated water contains
chemical compounds calledchemical compounds called
trihalomethanes.trihalomethanes.
 These are carcinogensThese are carcinogens
resulting from theresulting from the
combination of chlorine withcombination of chlorine with
organic compounds in water.organic compounds in water.
 These chemicals, also knownThese chemicals, also known
as organochlorides, do notas organochlorides, do not
degrade very well and aredegrade very well and are
generally stored in the fattygenerally stored in the fatty
tissues of the body (breast,tissues of the body (breast,
other fatty areas, mother'sother fatty areas, mother's
milk, blood and semen).

37. Organochlorides can causeOrganochlorides can cause
mutations by altering DNA,mutations by altering DNA,
supress immune function andsupress immune function and
interfere with the naturalinterfere with the natural
controls of cell growth.controls of cell growth.

38.  Chlorine has beenChlorine has been
documented to aggravatedocumented to aggravate
asthma, especially in thoseasthma, especially in those
children who make frequentchildren who make frequent
use of chlorinated swimminguse of chlorinated swimming
pools.pools.
 Several studies also linkSeveral studies also link
chlorine and chlorinated by-chlorine and chlorinated by-
products to a greaterproducts to a greater
incidence of bladder, breastincidence of bladder, breast
and bowel cancer as well asand bowel cancer as well as
malignant melanoma.malignant melanoma.

39. Chlorine Toxicity LimitsChlorine Toxicity Limits
 The exact levels whereThe exact levels where
chlorine becomes toxic is notchlorine becomes toxic is not
clear.clear.
 About 0.2-0.5 mcg. intakeAbout 0.2-0.5 mcg. intake
daily is probably safe.daily is probably safe.
 Below 0.2 ppm is consideredBelow 0.2 ppm is considered
current normal ranges forcurrent normal ranges for
body chlorine levels.body chlorine levels.
 There should not be anyThere should not be any
inorganic chlorine present ininorganic chlorine present in
the body.the body.

40.  Water purification actually
accounts for only a small fraction of
the chlorine produced each year,
however.
 About three times as much of the
element is used as a bleach in the
paper and pulp industry.
 The most important use of chlorine is
to make other chemicals.
 For example, chlorine can be reactedFor example, chlorine can be reacted
withwith etheneethene (ethylene; C2H2) gas to(ethylene; C2H2) gas to
make ethylene dichloride.make ethylene dichloride.

41.  Ethylene dichloride is the starting
material for the production of
polyvinyl chloride, used to make
piping, tubing, flooring, siding, film,
coatings, and many other products.
 Chlorine is also used extensively in
the manufacture of propylene oxide,
from which the class of plastics
known as polyesters is made.
 Polyesters are found in a wide range
of materials, including car and boat
bodies, bowling balls, fabrics for
clothing, and rugs.

42.  Manufacture of chlorofluorocarbons
(CFCs) was one of the major uses of
chlorine.
 They are chemically very stable, non-
flammable, non-toxic, and easily
liquefied.
 They found use in applications such as
air conditioning and refrigeration
systems, aerosol spray products, and
cleaning materials.
 At the peak of their popularity, more
than 700 million kilograms (1.5 billion
pounds) of these compounds were
being made every year.

43.  CFCs can cause serious harm to the
Earth's atmosphere.
 CFC molecules react with and destroy
ozone in the Earth's stratosphere.
 This reaction has serious
consequences for life on Earth since
ozone blocks out ultraviolet radiation
from the Sun that may have harmful
effects on both plants and animals.
 Today, the production and use of
CFCs is largely banned in most parts
of the world.

44.  Health Issues
 Chlorine gas is extremely toxic.
 In small doses, it irritates the nose
and throat, causing sneezing, runny
nose, and red eyes.
 Larger doses of chlorine can be fatal.
 In fact, chlorine gas has been used in
a number of wars throughout history,
most notably in World War I.
 German armies used the gas as a
weapon, causing many deaths and
permanent injuries to Allied soldiers.

45.  On the other hand, compounds of
chlorine are essential in
maintaining good health in humans
and other animals.
 The average human body contains
about about 3.5 ounces (95 grams)
of chlorine, primarily in the form of
 hydrochloric acid (HCl; "stomach
acid"),
 sodium chloride (NaCl), and
 potassium chloride (KCl).

46.  Chlorine is one of five closely related
chemical elements called halogens,
or "salt-formers, " because they
readily combine with metals to make
salts.
 In fact, chlorine is one of the most
reactive elements known.
 When exposed to sunlight, a mixture
of chlorine and hydrogen will violently
explode.
 In nature, chlorine is always found in
compounds, never as a free element.
 Its most common compound is
ordinary table salt, sodium chloride.

47.  TheThe automobileautomobile industry reliesindustry relies
heavily on chlorine because carsheavily on chlorine because cars
contain many components thatcontain many components that
use chlorine in their manufacture.use chlorine in their manufacture.
 Three chlorine products,Three chlorine products,
 PVC,PVC,
 pickled steel, andpickled steel, and
 paint create more jobs in thepaint create more jobs in the
developing world.developing world.

48.  Industrially, chlorine is also used inIndustrially, chlorine is also used in
massive quantities formassive quantities for sanitationsanitation
purposes.purposes.
 An important advancement in publicAn important advancement in public
health has been the widespreadhealth has been the widespread
chlorinationchlorination of drinking water.of drinking water.
 Chlorine-based water purifyingChlorine-based water purifying
chemicals were first introduced inchemicals were first introduced in
1908.1908.
 Chlorine water purification hasChlorine water purification has
practically eradicated diseases thatpractically eradicated diseases that
were once devastating, such aswere once devastating, such as
choleracholera and dysentery.and dysentery.

49.  Because it is so highly reactive,Because it is so highly reactive,
chlorine is one of the mostchlorine is one of the most
effective germicides available.effective germicides available.
 Chlorine chemicals kill bacteria,Chlorine chemicals kill bacteria,
algae,algae, fungifungi, and protozoans and, and protozoans and
inactivate viruses.inactivate viruses.
 Simple household bleach, sodiumSimple household bleach, sodium
hypochlorite, can even inactivatehypochlorite, can even inactivate
and sterilize equipment from suchand sterilize equipment from such
deadly viruses as thedeadly viruses as the EbolaEbola
virusvirus..

50.  Chlorine disinfectants are
used to prevent institutional
disease transmission
 in food preparation,
 day care centers,
 nursing homes, and
 hospitals.

51.  Chlorine is a vital chemical in theChlorine is a vital chemical in the
pharmaceutical and medicalpharmaceutical and medical
industries.industries.
 Approximately 85% of all drugsApproximately 85% of all drugs
either contain chlorine or areeither contain chlorine or are
manufactured using chlorine.manufactured using chlorine.
 The chemical addition of chlorineThe chemical addition of chlorine
to a drug molecule can enhanceto a drug molecule can enhance
itsits absorptionabsorption and delay itsand delay its
elimination from the body,elimination from the body,
increasing the duration of itsincreasing the duration of its
action.action.

52.  ChlorinatedChlorinated hydrocarbonshydrocarbons areare
specific hydrocarbon molecules thatspecific hydrocarbon molecules that
also have atoms of the elementalso have atoms of the element
chlorine chemically bonded to them.chlorine chemically bonded to them.
 Chlorinated hydrocarbons includeChlorinated hydrocarbons include
products such as the synthetic rubbersproducts such as the synthetic rubbers
used in car tires and tennis shoes.used in car tires and tennis shoes.
 They are also used in packagingThey are also used in packaging
plasticsplastics, and a variety of products, and a variety of products
such as fluid pipes, furniture, homesuch as fluid pipes, furniture, home
siding, credit cards, fences, and toys.siding, credit cards, fences, and toys.
 Chlorinated hydrocarbons also can beChlorinated hydrocarbons also can be
used as precursors in the production ofused as precursors in the production of
non-stick coatings such as Teflon.non-stick coatings such as Teflon.

53.  In addition to their use in theIn addition to their use in the
manufacture of polymers, rubbers,manufacture of polymers, rubbers,
plastics, solvents, and cleaners,plastics, solvents, and cleaners,
chlorinated hydrocarbons also arechlorinated hydrocarbons also are
powerful pesticides.powerful pesticides.
 They rank among the most potentThey rank among the most potent
and environmentally persistentand environmentally persistent
insecticides, and when combinedinsecticides, and when combined
with fluorine, they yield thewith fluorine, they yield the
refrigerants calledrefrigerants called
chlorofluorocarbonschlorofluorocarbons , or CFCs., or CFCs.

54.  The reaction between chlorine and
other elements can often be vigorous.
 For example, chlorine reacts
explosively with hydrogen to form
hydrogen chloride:
 H2 + Cl2 -> 2HCI
 Chlorine does not burn but, like
oxygen, it helps other substances
burn.
 Chlorine is a strong oxidizing agent (a
chemical substance that gives up or
takes on electrons from another
substance).

55.  Two naturally occurring isotopes of
chlorine exist, chlorine-35 and chlorine-
36.
 One radioactive isotope of chlorine is
used in research. That is chlorine-36.
 This isotope is used because compounds
of chlorine occur so commonly in
everyday life.
 The behavior of these compounds can be
studied if chlorine-36 is used as a tracer.
 The radioactive chlorine, chlorine-36,
gives off radiation.
 That radiation can be detected by
holding an instrument near the
experiment.

56. Chlorine cycleChlorine cycle
 The study of chlorine cycleThe study of chlorine cycle
is very important since itis very important since it
has a great role in thehas a great role in the
depletion of ozone similardepletion of ozone similar
to NO and N02.to NO and N02.

57.  The mechanisms involved inThe mechanisms involved in
the chlorine cycle are asthe chlorine cycle are as
follows :follows :
 1. Movement of marine NaCI +1. Movement of marine NaCI +
aerosols from atmosphere toaerosols from atmosphere to
hydrosphere and lithospherehydrosphere and lithosphere
-through-through
 sedimentation,sedimentation,
 rain andrain and
 wind action.wind action.

58.  2. Movement of HCI, CI,2. Movement of HCI, CI,
C10 and NH4C1 aerosolsC10 and NH4C1 aerosols
from atmosphere tofrom atmosphere to
Lithosphere andLithosphere and
hydrosphere –throughhydrosphere –through
 volcanoes,volcanoes,
 rain andrain and
 sedimentation.sedimentation.

59.  3. Transformation of3. Transformation of
chlorocarbons andchlorocarbons and
chlorofluoro carbonschlorofluoro carbons
into other atmosphericinto other atmospheric
compounds bycompounds by
stratosphericstratospheric
decomposition.decomposition.

60.  4. Transformation of4. Transformation of
biospheric, lithosphericbiospheric, lithospheric
and hydrospheric chlorideand hydrospheric chloride
into chlorofluoro carbonsinto chlorofluoro carbons
by fermentation,by fermentation,
combustion,combustion,
 marine algae,marine algae,
 refrigerators, etc.refrigerators, etc.

61. Marine
NaCl
HYDROSPHERE/
LITHOSPHERE
CHLORIDES
SEDIMENTS AND
WIND

62. Atmosphere
HYDROSPHERE/
LITHOSPHERE
CHLORIDES
Volcanoes and
rainout

63. HYDROSPHERE/
LITHOSPHERE
-CHLORIDES
BIOSPHERE
CHLORINE
PLANT ROOTS & MARINE
ORGANISMS

64. BIOSPHERE
CHLORINE
CHLOROCARBONS/
CFCs
FERMENTATION,
COMBUSTION &
MARINE ALGAE

65.  5. Movement of chlorides5. Movement of chlorides
between biosphere, hydrospherebetween biosphere, hydrosphere
and lithosphere throughand lithosphere through
biological decay, plant roots andbiological decay, plant roots and
marine organisms.marine organisms.

66. Thank YouThank You