Water chemistry and corrosion
VishnuThumma
1,111 views
118 slides
Oct 01, 2021
Slide 1 of 118
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
About This Presentation
Water Chemistry: Hardness of water, EDTA Method, Ion Exchange Method, Reverse Osmosis, Chlorination.
Corrosion: Definition, Cause and Effects, Types of corrosion, Oxidation corrosion, Electrochemical Corrosion, Factors influencing corrosion, Waterline corrosion, Pitting corrosion, Cathodic protectio...
Slide Content
MATRUSRI ENGINEERING COLLEGE
DEPARTMENT OF SCIENCES AND HUMANITIES
SUBJECT NAME: CHEMISTRY
FACULTY NAME: VISHNU THUMMA
MATRUSRI
ENGINEERING COLLEGE
TOPIC: WATER CHEMISTRY AND CORROSION
DEPARTMENT OF SCIENCES AND HUMANITIES
SUBJECT NAME: CHEMISTRY
FACULTY NAME: VISHNU THUMMA
MATRUSRI
ENGINEERING COLLEGE
TOPIC: WATER CHEMISTRY AND CORROSION
CHEMISTRY
COURSEOBJECTIVES:
➢Correlatethepropertiesofmaterialswiththeirinternalstructureanduse
theforEngineeringapplications
➢Applytheprinciplesofelectrochemistryinstorageofelectricalenergyin
batteries.
➢Gainsknowledgeincausesofcorrosionanditsprevention.
➢Attainsknowledgeaboutthedisadvantagesofhardwaterfordomestic
andindustrialpurposes.
➢Alsolearnsthetechniquesofsofteningofhardwaterandtreatmentof
waterfordrinkingpurpose.
➢Exposedtoqualitativeandquantitativeparametersofchemicalfuels.
➢Awareeco-friendlymaterialsandprocesses.
MATRUSRI
ENGINEERING COLLEGE
2
COURSEOBJECTIVES:
➢Correlatethepropertiesofmaterialswiththeirinternalstructureanduse
theforEngineeringapplications
➢Applytheprinciplesofelectrochemistryinstorageofelectricalenergyin
batteries.
➢Gainsknowledgeincausesofcorrosionanditsprevention.
➢Attainsknowledgeaboutthedisadvantagesofhardwaterfordomestic
andindustrialpurposes.
➢Alsolearnsthetechniquesofsofteningofhardwaterandtreatmentof
waterfordrinkingpurpose.
➢Exposedtoqualitativeandquantitativeparametersofchemicalfuels.
➢Awareeco-friendlymaterialsandprocesses.
MATRUSRI
ENGINEERING COLLEGE
2
CHEMISTRY
COURSEOUTCOMES:Aftercompletionofcoursestudentswillbeableto
➢Analyzeandapplyknowledgeofelectrodicsincalculationofcell
potentialsofbatteries.
➢Identifythedifferenttypesofhardnessandalkalinitiesinwaterand
makeuseofsofteningmethods,analyzeandapplytheknowledgeof
corrosionforitsprevention.
➢Discussdifferenttypesofpolymersbasedontheirendonuseandthe
needtoreplacetheconventionalpolymerswithpolymersofengineering
applications.
➢Identifyandanalyzedifferenttypesofchemicalfuelsfordomesticand
automobileapplications.
➢Outlinetheprinciplesofgreenchemistryforsustainableenvironment
andpreparationofbiodieselfromrenewablesources.
MATRUSRI
ENGINEERING COLLEGE
3
COURSEOUTCOMES:Aftercompletionofcoursestudentswillbeableto
➢Analyzeandapplyknowledgeofelectrodicsincalculationofcell
potentialsofbatteries.
➢Identifythedifferenttypesofhardnessandalkalinitiesinwaterand
makeuseofsofteningmethods,analyzeandapplytheknowledgeof
corrosionforitsprevention.
➢Discussdifferenttypesofpolymersbasedontheirendonuseandthe
needtoreplacetheconventionalpolymerswithpolymersofengineering
applications.
➢Identifyandanalyzedifferenttypesofchemicalfuelsfordomesticand
automobileapplications.
➢Outlinetheprinciplesofgreenchemistryforsustainableenvironment
andpreparationofbiodieselfromrenewablesources.
MATRUSRI
ENGINEERING COLLEGE
3
UNIT-II WATER CHEMISTRY AND CORROSION
MATRUSRI
ENGINEERING COLLEGE
Definition:Corrosionistheprocessofgradualdeteriorationofametalfrom
itssurfaceduetoanunwantedchemicalorelectrochemicalinteractionof
metalwithitsenvironment.
4
OUTCOMES:AftercompletionofcoursestudentswillbeabletoIdentifythedifferent
typesofhardnessandalkalinitiesinwaterandmakeuseofsofteningmethods,analyze
andapplytheknowledgeofcorrosionforitsprevention.
MODULE-I: INTRODUCTION TO CORROSION
Ex:Reddishbrown
scaleandpowderof
rust(Fe
2O
3.3H
2O)on
thesurfaceofiron.
Greenfilmofbasic
carbonate
[CaCO
3+Cu(OH)
2]
onthesurfaceof
copper.
MATRUSRI
ENGINEERING COLLEGE
Definition:Corrosionistheprocessofgradualdeteriorationofametalfrom
itssurfaceduetoanunwantedchemicalorelectrochemicalinteractionof
metalwithitsenvironment.
4
OUTCOMES:AftercompletionofcoursestudentswillbeabletoIdentifythedifferent
typesofhardnessandalkalinitiesinwaterandmakeuseofsofteningmethods,analyze
andapplytheknowledgeofcorrosionforitsprevention.
MODULE-I: INTRODUCTION TO CORROSION
Ex:Reddishbrown
scaleandpowderof
rust(Fe
2O
3.3H
2O)on
thesurfaceofiron.
Greenfilmofbasic
carbonate
[CaCO
3+Cu(OH)
2]
onthesurfaceof
copper.
Cause of Corrosion
5
MATRUSRI
ENGINEERING COLLEGE
Mostmetals(withtheexceptionofnoblemetalssuchasAu,Pt,etc.)existinnaturein
combinedformsastheiroxides,carbonates,hydroxides,sulphides,chloridesandsilicates.
Thesechemicallycombinedstatesofmetalareknownas‘ores’.
These chemically combined states of metal are thermodynamically more stable states for
metal.
5
MATRUSRI
ENGINEERING COLLEGE
Mostmetals(withtheexceptionofnoblemetalssuchasAu,Pt,etc.)existinnaturein
combinedformsastheiroxides,carbonates,hydroxides,sulphides,chloridesandsilicates.
Thesechemicallycombinedstatesofmetalareknownas‘ores’.
These chemically combined states of metal are thermodynamically more stable states for
metal.
Cause of Corrosion
6
MATRUSRI
ENGINEERING COLLEGE
Duringextractionofmetals,considerableamountsofenergyarerequiredinmetallurgy.
Consequently,isolatedpuremetalscanberegardedinahigherenergystatewhichare
thermodynamicallyunstablethantheircorrespondingores.
That is why, metals have a natural tendency to revert back to combined state
(thermodynamically more stable state).
6
MATRUSRI
ENGINEERING COLLEGE
Duringextractionofmetals,considerableamountsofenergyarerequiredinmetallurgy.
Consequently,isolatedpuremetalscanberegardedinahigherenergystatewhichare
thermodynamicallyunstablethantheircorrespondingores.
That is why, metals have a natural tendency to revert back to combined state
(thermodynamically more stable state).
Cause of Corrosion
7
MATRUSRI
ENGINEERING COLLEGE
Asaresultwhenmetalsareputintouse,invariousforms,theyareexposedtoenvironment
suchasdrygases,moisture,liquids,etc.theexposedmetalsurfacesbegintodecayand
formmorestablecompoundsofmetalslikeoxides,carbonates,etc.
Thus, corrosion is a process “reverse of extraction of metals”.
7
MATRUSRI
ENGINEERING COLLEGE
Asaresultwhenmetalsareputintouse,invariousforms,theyareexposedtoenvironment
suchasdrygases,moisture,liquids,etc.theexposedmetalsurfacesbegintodecayand
formmorestablecompoundsofmetalslikeoxides,carbonates,etc.
Thus, corrosion is a process “reverse of extraction of metals”.
Effects of Corrosion
8
MATRUSRI
ENGINEERING COLLEGE
8
MATRUSRI
ENGINEERING COLLEGE
•Thevaluablemetallicpropertieslikeconductivity,malleability,ductilityetc.
arelostduetocorrosionandthuslossofefficiency.
•Theprocessofcorrosionisnotincurredandisresponsibleforthe
enormouswastageofmachines,equipmentanddifferenttypesofmetallic
products.
•Lossesoccurringduetocorrosioncannotbemeasuredintermsofthecost
ofmetalsalone,butthehighcostoffabricationintoequipment/machine
tool/structuresshouldalsobeconsidered.
•Theapproximateestimateoflossofmetalduetocorrosion,as2to2.5
billiondollarsperannumall-overtheworld.
Effects of Corrosion
9
MATRUSRI
ENGINEERING COLLEGE
arelostduetocorrosionandthuslossofefficiency.
•Theprocessofcorrosionisnotincurredandisresponsibleforthe
enormouswastageofmachines,equipmentanddifferenttypesofmetallic
products.
•Lossesoccurringduetocorrosioncannotbemeasuredintermsofthecost
ofmetalsalone,butthehighcostoffabricationintoequipment/machine
tool/structuresshouldalsobeconsidered.
•Theapproximateestimateoflossofmetalduetocorrosion,as2to2.5
billiondollarsperannumall-overtheworld.
Effects of Corrosion
9
MATRUSRI
ENGINEERING COLLEGE
The corrosion process proceeds in two types by chemical and electrochemical
attack of environment.
A) Dry or Chemical Corrosion
B)Wet or Electrochemical Corrosion
Types of Corrosion
10
MATRUSRI
ENGINEERING COLLEGE
attack of environment.
A) Dry or Chemical Corrosion
B)Wet or Electrochemical Corrosion
Types of Corrosion
10
MATRUSRI
ENGINEERING COLLEGE
QUIZ
1.Theprocessofdeteriorationofametalformitssurfaceduetounwanted
chemicalorelectrochemicalinteractionofthemetalwithitsenvironmentis
called
a)electrolysisb)electrodialysis c)corrosion d)deposition
2.Metalsexistinthenatureintheformof
a)mineral b)ores c)combinedstate d)alltheabove
3.Metalsundergocorrosiondueto
a)pureformofmetalisthermodynamicallyunstable.
b)pureformofmetalisthermodynamicallystable.
c)pureformofmetalisregardedaslowenergystate
d)alltheabove
4.Lossofcorrosionis
a)lossofmetallicpropertiesd)metallurgycostc)designcostd)alltheabove
11
MATRUSRI
ENGINEERING COLLEGE
1.Theprocessofdeteriorationofametalformitssurfaceduetounwanted
chemicalorelectrochemicalinteractionofthemetalwithitsenvironmentis
called
a)electrolysisb)electrodialysis c)corrosion d)deposition
2.Metalsexistinthenatureintheformof
a)mineral b)ores c)combinedstate d)alltheabove
3.Metalsundergocorrosiondueto
a)pureformofmetalisthermodynamicallyunstable.
b)pureformofmetalisthermodynamicallystable.
c)pureformofmetalisregardedaslowenergystate
d)alltheabove
4.Lossofcorrosionis
a)lossofmetallicpropertiesd)metallurgycostc)designcostd)alltheabove
11
MATRUSRI
ENGINEERING COLLEGE
Thistypeofcorrosionoccursbydirectchemicalreactionsbetweenthe
environmentandthemetalsandalloys.
Presenceofanelectrolyteisnotatallessentialforthecorrosiontooccur.
Eg:Directchemicalactionofenvironmentalgasessuchasoxygen,halogens,
hydrogensulphide,sulphurdioxide,nitrogenoranhydrousinorganicliquid
withthemetal.
MODULE-2: DRY OR CHEMICAL CORROSION
12
MATRUSRI
ENGINEERING COLLEGE
environmentandthemetalsandalloys.
Presenceofanelectrolyteisnotatallessentialforthecorrosiontooccur.
Eg:Directchemicalactionofenvironmentalgasessuchasoxygen,halogens,
hydrogensulphide,sulphurdioxide,nitrogenoranhydrousinorganicliquid
withthemetal.
MODULE-2: DRY OR CHEMICAL CORROSION
12
MATRUSRI
ENGINEERING COLLEGE
a) Oxidation corrosion,
b) Corrosion by other gases,
c) Liquid metal corrosion.
There are three main types of chemical corrosion:
13
MATRUSRI
ENGINEERING COLLEGE
b) Corrosion by other gases,
c) Liquid metal corrosion.
There are three main types of chemical corrosion:
13
MATRUSRI
ENGINEERING COLLEGE
Direct action of oxygen at high or low temperatures on metals in the absence of moisture
is called oxidation corrosion.
2 M →2 M
n+
+ 2n e
-
n/2 O
2+ 2n e
-
→n O
2-
2 M + n/2 O
2 →2 M
n+
+ n O
2-
Oxidationoccurfirstatthesurfaceofthemetalbyformingametaloxidescalewhichacts
asabarrierbetweenmetalsurfaceandenvironment.
Thenatureofoxideformedplaysanimportantroleinoxidationcorrosionprocesswhich
decidesfurtheraction.
Oxidation corrosion
14
MATRUSRI
ENGINEERING COLLEGE
is called oxidation corrosion.
2 M →2 M
n+
+ 2n e
-
n/2 O
2+ 2n e
-
→n O
2-
2 M + n/2 O
2 →2 M
n+
+ n O
2-
Oxidationoccurfirstatthesurfaceofthemetalbyformingametaloxidescalewhichacts
asabarrierbetweenmetalsurfaceandenvironment.
Thenatureofoxideformedplaysanimportantroleinoxidationcorrosionprocesswhich
decidesfurtheraction.
Oxidation corrosion
14
MATRUSRI
ENGINEERING COLLEGE
Iftheoxidefilmformediscontinuesandrigidlyadheredtothesurfaceofmetalis
imperviousinnature,andiscalledstableoxidelayer.
Itisprotectiveandshieldsthemetalfromfurthercorrosion.
Ex:OxidefilmsonAl,Sn,Pb,Cuetc.actsasaprotectivecoatingandfurther
corrosionisprevented.
If unstable oxide film is formed, it decomposes back into the metal and oxygen.
Consequently, oxidation corrosion is not possible.
Ex: Noble metals like Ag, Au and Pt do not undergo corrosion.
15
MATRUSRI
ENGINEERING COLLEGE
imperviousinnature,andiscalledstableoxidelayer.
Itisprotectiveandshieldsthemetalfromfurthercorrosion.
Ex:OxidefilmsonAl,Sn,Pb,Cuetc.actsasaprotectivecoatingandfurther
corrosionisprevented.
If unstable oxide film is formed, it decomposes back into the metal and oxygen.
Consequently, oxidation corrosion is not possible.
Ex: Noble metals like Ag, Au and Pt do not undergo corrosion.
15
MATRUSRI
ENGINEERING COLLEGE
If oxide layer formed is volatile, it is non-protective and more feasible for further attack of
environment.
This causes rapid and continuous corrosion, leading to excessive corrosion.
Ex: Mo forms a volatile oxide layer.
Ifoxidelayerishavingporesorcracks,theatmosphericoxygenhaveaccesstothe
underlyingsurfaceofmetal,throughtheporesorcracksofthelayer,therebythe
corrosioncontinuesunobstructedtilltheentiremetaliscompletelyconvertedintoits
oxide.
16
MATRUSRI
ENGINEERING COLLEGE
environment.
This causes rapid and continuous corrosion, leading to excessive corrosion.
Ex: Mo forms a volatile oxide layer.
Ifoxidelayerishavingporesorcracks,theatmosphericoxygenhaveaccesstothe
underlyingsurfaceofmetal,throughtheporesorcracksofthelayer,therebythe
corrosioncontinuesunobstructedtilltheentiremetaliscompletelyconvertedintoits
oxide.
16
MATRUSRI
ENGINEERING COLLEGE
Accordingtoit,‘”greateristhespecificvolumeratio,lesseristherateofcorrosion.”
Ifthevolumeofmetaloxidelayerisatleastasgreatasthevolumeofmetalfromwhichit
isformedisnon-porousandbecomesprotectivelayerbytightlyadheringtothebase
metal.
Ex:ThespecificvolumeratiosofW,CrandNiare3.6,2.0and1.6respectively.
Hence,therateofcorrosionisleastinTungsten(W).
Ifthevolumeofmetaloxideislessthanthevolumeofthemetal,theoxidelayeris
porous,noncontinuousandnon-protectiveandfacesstrains.
Hence,cracksandporesaredevelopedinthelayer,creatingaccesstoatmospheric
oxygentoreachtheunderlyingmetal.Inthiscasecorrosioniscontinuousandrapidly
increases.
Ex:Li,NaandK.
Pilling-Bedworthrule:
17
MATRUSRI
ENGINEERING COLLEGE
Ifthevolumeofmetaloxidelayerisatleastasgreatasthevolumeofmetalfromwhichit
isformedisnon-porousandbecomesprotectivelayerbytightlyadheringtothebase
metal.
Ex:ThespecificvolumeratiosofW,CrandNiare3.6,2.0and1.6respectively.
Hence,therateofcorrosionisleastinTungsten(W).
Ifthevolumeofmetaloxideislessthanthevolumeofthemetal,theoxidelayeris
porous,noncontinuousandnon-protectiveandfacesstrains.
Hence,cracksandporesaredevelopedinthelayer,creatingaccesstoatmospheric
oxygentoreachtheunderlyingmetal.Inthiscasecorrosioniscontinuousandrapidly
increases.
Ex:Li,NaandK.
Pilling-Bedworthrule:
17
MATRUSRI
ENGINEERING COLLEGE
IntheabsenceofmoistureafewgaseslikeSO
2,CO
2,Cl
2,H
2SandF
2etc.attackthe
metal.
Thedegreeofcorrosiondependsontheformationofprotectiveornon-protectivefilmson
themetalsurface.
Ifthefilmformedisprotectiveornon-porous,theintensityorextentofattackdecreases,
becausethefilmformedprotectsthemetalfromfurtherattack.
Ex:AgClfilm,resultingfromtheattackofCl
2onAg.
Ifthefilmformedisnon-protectiveorporous,thesurfaceofthewholemetalisgradually
destroyed.
Ex:DryCl
2gasattacksontin(Sn)formingvolatileSnCl
4.H
2Sathightemperature
attackssteelformingaFeSscaleinpetroleumindustry.
Corrosion by other gases:
18
MATRUSRI
ENGINEERING COLLEGE
2,CO
2,Cl
2,H
2SandF
2etc.attackthe
metal.
Thedegreeofcorrosiondependsontheformationofprotectiveornon-protectivefilmson
themetalsurface.
Ifthefilmformedisprotectiveornon-porous,theintensityorextentofattackdecreases,
becausethefilmformedprotectsthemetalfromfurtherattack.
Ex:AgClfilm,resultingfromtheattackofCl
2onAg.
Ifthefilmformedisnon-protectiveorporous,thesurfaceofthewholemetalisgradually
destroyed.
Ex:DryCl
2gasattacksontin(Sn)formingvolatileSnCl
4.H
2Sathightemperature
attackssteelformingaFeSscaleinpetroleumindustry.
Corrosion by other gases:
18
MATRUSRI
ENGINEERING COLLEGE
It is due to chemical action of flowing liquid metal at high temperatures on solid metal or
alloy. Such corrosion occurs in devices used for nuclear power.
The corrosion reaction involves either dissolution of a solid metal by a liquid metal or
internal penetration of the liquid metal into the solid metal.
Both these modes of corrosion cause weakening of the solid metal.
Liquid Metal Corrosion:
19
MATRUSRI
ENGINEERING COLLEGE
alloy. Such corrosion occurs in devices used for nuclear power.
The corrosion reaction involves either dissolution of a solid metal by a liquid metal or
internal penetration of the liquid metal into the solid metal.
Both these modes of corrosion cause weakening of the solid metal.
Liquid Metal Corrosion:
19
MATRUSRI
ENGINEERING COLLEGE
QUIZ
1.Which of the following is not dry corrosion?
a) oxidation corrosion b) rusting of iron
c) corrosion by gases d) liquid metal corrosion
2. Direct action of environment on metal surface is called
a) chemical corrosion b) electrochemical corrosion
c) wet corrosion d) none
3. Type of corrosion product layer which prevents further action of environment
a) stable oxide layer b) volatile oxide layer
c) porous oxide layer d) all the above
4. When specific volume ration is high
a) Corrosion is high b)Corrosion is low
c) No change in corrosion rated) none
20
MATRUSRI
ENGINEERING COLLEGE
1.Which of the following is not dry corrosion?
a) oxidation corrosion b) rusting of iron
c) corrosion by gases d) liquid metal corrosion
2. Direct action of environment on metal surface is called
a) chemical corrosion b) electrochemical corrosion
c) wet corrosion d) none
3. Type of corrosion product layer which prevents further action of environment
a) stable oxide layer b) volatile oxide layer
c) porous oxide layer d) all the above
4. When specific volume ration is high
a) Corrosion is high b)Corrosion is low
c) No change in corrosion rated) none
20
MATRUSRI
ENGINEERING COLLEGE
Wet corrosion or electrochemical corrosion takes place under wet or moist
conditions through the formation of short circuited tiny electrochemical cells.
Wet corrosion is more common than dry corrosion.
This type of corrosion can be observed
i) When a metal is in contact with conducting liquid (or)
ii) When two dissimilar metals are dipped partially in a solution.
This corrosion occurs due to the existence of separate ‘anodic’ and ‘cathodic’
areas between which current flows through the conducting solution.
MODULE-3: ELECTROCHEMICAL CORROSION
21
MATRUSRI
ENGINEERING COLLEGE
conditions through the formation of short circuited tiny electrochemical cells.
Wet corrosion is more common than dry corrosion.
This type of corrosion can be observed
i) When a metal is in contact with conducting liquid (or)
ii) When two dissimilar metals are dipped partially in a solution.
This corrosion occurs due to the existence of separate ‘anodic’ and ‘cathodic’
areas between which current flows through the conducting solution.
MODULE-3: ELECTROCHEMICAL CORROSION
21
MATRUSRI
ENGINEERING COLLEGE
➢The formation of anodic and cathodicareas or parts in contact with each
other.
➢Presence of a conducting medium.
➢Corrosion of anodic areas only.
➢Formation of corrosion product somewhere between anodic and cathodic
areas.
Electrochemical Corrosion involves:
22
MATRUSRI
ENGINEERING COLLEGE
other.
➢Presence of a conducting medium.
➢Corrosion of anodic areas only.
➢Formation of corrosion product somewhere between anodic and cathodic
areas.
Electrochemical Corrosion involves:
22
MATRUSRI
ENGINEERING COLLEGE
Involves flow of electron-current between the anodic and cathodicareas.
The anodic reaction involves in dissolution of metal as corresponding metallic ions with
the liberation of free electrons.
At anodic area: M →M
n+
+ n e
-
(Oxidation)
The cathodicreaction consumes electrons with either by
i) evolution of hydrogen, or
ii) absorption of oxygen
depending on the nature of the corrosive environment.
Mechanism of Electrochemical Corrosion:
23
MATRUSRI
ENGINEERING COLLEGE
The anodic reaction involves in dissolution of metal as corresponding metallic ions with
the liberation of free electrons.
At anodic area: M →M
n+
+ n e
-
(Oxidation)
The cathodicreaction consumes electrons with either by
i) evolution of hydrogen, or
ii) absorption of oxygen
depending on the nature of the corrosive environment.
Mechanism of Electrochemical Corrosion:
23
MATRUSRI
ENGINEERING COLLEGE
It occurs usually in acidic environment.
Ex: Fe →Fe
2+
+ 2e
-
(Oxidation)
These electrons flow through the metal, from anode to cathode, where H
+
ions are
eliminated as hydrogen gas from acidic solution.
2 H
+
+ 2 e
-
→H
2(Reduction)
The overall reaction: Fe + 2 H
+
→Fe
2+
+ H
2
Evolution of Hydrogen:
24
MATRUSRI
ENGINEERING COLLEGE
Ex: Fe →Fe
2+
+ 2e
-
(Oxidation)
These electrons flow through the metal, from anode to cathode, where H
+
ions are
eliminated as hydrogen gas from acidic solution.
2 H
+
+ 2 e
-
→H
2(Reduction)
The overall reaction: Fe + 2 H
+
→Fe
2+
+ H
2
Evolution of Hydrogen:
24
MATRUSRI
ENGINEERING COLLEGE
Thus,thistypeofcorrosioncauses“displacementofhydrogenionsfromtheacidic
solutionbymetalions.“
Consequently,allmetalsabovehydrogenintheelectrochemicalserieshaveatendency
togetdissolvedinacidicsolutionwithsimultaneousevolutionofhydrogen.
Itmaybenotedthatinhydrogenevolutiontypecorrosiontheanodesareusuallyvery
largeinareaswhereasthecathodesaresmallareas.
Evolution of Hydrogen
25
MATRUSRI
ENGINEERING COLLEGE
solutionbymetalions.“
Consequently,allmetalsabovehydrogenintheelectrochemicalserieshaveatendency
togetdissolvedinacidicsolutionwithsimultaneousevolutionofhydrogen.
Itmaybenotedthatinhydrogenevolutiontypecorrosiontheanodesareusuallyvery
largeinareaswhereasthecathodesaresmallareas.
Evolution of Hydrogen
25
MATRUSRI
ENGINEERING COLLEGE
•Occurs in the presence of atmospheric oxygen.
•Rusting of Iron is a common example of this type of corrosion.
•Usually the surface of iron is coated with a thin film of iron oxide.
•However, if this iron oxide film develops some cracks, anodic areas are
created on the surface while the well-metal parts act as cathodes.
•If follows that the anodic areas are small surface parts while nearly the rest
of the surface of the metal forms large cathodes.
Absorption of Oxygen
26
MATRUSRI
ENGINEERING COLLEGE
•Rusting of Iron is a common example of this type of corrosion.
•Usually the surface of iron is coated with a thin film of iron oxide.
•However, if this iron oxide film develops some cracks, anodic areas are
created on the surface while the well-metal parts act as cathodes.
•If follows that the anodic areas are small surface parts while nearly the rest
of the surface of the metal forms large cathodes.
Absorption of Oxygen
26
MATRUSRI
ENGINEERING COLLEGE
Attheanodicareas,themetal(iron)dissolvesasferrousionswithliberationofelectrons.
Fe→Fe
2+
+2e
-
(Oxidation)
Theliberatedelectronsflowfromanodictocathodicareas,throughironmetal,where
electronsareinterceptedbythedissolvedoxygenas:
½O
2+H
2O+2e
-
→2OH
-
(Reduction)
TheFe
2+
ionsatanodeandOH
-
ionsatcathodediffusethroughmediumandwhenthey
meet,ferroushydroxideisprecipitated.
Fe
2+
+2OH
-
→Fe(OH)
2↓
27
MATRUSRI
ENGINEERING COLLEGE
Absorption of Oxygen
Fe→Fe
2+
+2e
-
(Oxidation)
Theliberatedelectronsflowfromanodictocathodicareas,throughironmetal,where
electronsareinterceptedbythedissolvedoxygenas:
½O
2+H
2O+2e
-
→2OH
-
(Reduction)
TheFe
2+
ionsatanodeandOH
-
ionsatcathodediffusethroughmediumandwhenthey
meet,ferroushydroxideisprecipitated.
Fe
2+
+2OH
-
→Fe(OH)
2↓
27
MATRUSRI
ENGINEERING COLLEGE
Absorption of Oxygen
Ifenoughoxygenispresent,ferroushydroxideiseasilyoxidizedtoferric
hydroxide.
4Fe(OH)
2+O
2+2H
2O→4Fe(OH)
3
Thisproductiscalledyellowrust,actuallycorrespondstoFe
2O
3.3H
2O.
Ifthesupplyofoxygenislimitedthecorrosionproductmaybeevenblack
anhydrousmagnetite,Fe
3O
4.
Anincreaseinoxygencontentforcesthecathodicreactiontoproducemore
OH
-
ionswhichinturnremovesmoreelectronsfromanodeandaccelerates
thecorrosion.
28
MATRUSRI
ENGINEERING COLLEGE
Absorption of Oxygen
hydroxide.
4Fe(OH)
2+O
2+2H
2O→4Fe(OH)
3
Thisproductiscalledyellowrust,actuallycorrespondstoFe
2O
3.3H
2O.
Ifthesupplyofoxygenislimitedthecorrosionproductmaybeevenblack
anhydrousmagnetite,Fe
3O
4.
Anincreaseinoxygencontentforcesthecathodicreactiontoproducemore
OH
-
ionswhichinturnremovesmoreelectronsfromanodeandaccelerates
thecorrosion.
28
MATRUSRI
ENGINEERING COLLEGE
Absorption of Oxygen
QUIZ
1.Electrochemical corrosion involves
a) Formation of anodic & cathodicareasb) Corrosion at anode
c) Conducting medium d) All the above
2.Rusting of iron is characterized by
a) absorption of oxygen b) small anodic areas
c) reddish brown scale d) all the above
3. In which of the case corrosion is more rapid
a) small anode & large cathodicareasb) volatile corrosion product
c) autocatalytic action of metal d) all the above
4. When supply of oxygen is limited the corrosion product may be
a) Fe2O3.3H2O b) Fe3O4 c) Fe2O3 d)Fe(OH)2
29
MATRUSRI
ENGINEERING COLLEGE
1.Electrochemical corrosion involves
a) Formation of anodic & cathodicareasb) Corrosion at anode
c) Conducting medium d) All the above
2.Rusting of iron is characterized by
a) absorption of oxygen b) small anodic areas
c) reddish brown scale d) all the above
3. In which of the case corrosion is more rapid
a) small anode & large cathodicareasb) volatile corrosion product
c) autocatalytic action of metal d) all the above
4. When supply of oxygen is limited the corrosion product may be
a) Fe2O3.3H2O b) Fe3O4 c) Fe2O3 d)Fe(OH)2
29
MATRUSRI
ENGINEERING COLLEGE
It is a case of differential aeration corrosion.
More prevalent in cases such as ocean going ships, water storage steel
tanks etc, in which a portion of metal is always under water.
MOLDULE-4: WATERLINE CORROSION
30
MATRUSRI
ENGINEERING COLLEGE
The water line corrosion takes place due to the formation of differential
oxygen concentration cell.
More prevalent in cases such as ocean going ships, water storage steel
tanks etc, in which a portion of metal is always under water.
MOLDULE-4: WATERLINE CORROSION
30
MATRUSRI
ENGINEERING COLLEGE
The water line corrosion takes place due to the formation of differential
oxygen concentration cell.
Thepartofthemetalbelowthewaterlineexposedonlytothedissolvedoxygen
whilethepartabovethewaterisexposedtohigherconcentrationofthe
atmosphereoxygen.
Thus, part of the metal below the water acts as anode and undergoes corrosion.
Waterline Corrosion
31
MATRUSRI
ENGINEERING COLLEGE
The part above the water line is free from corrosion.
whilethepartabovethewaterisexposedtohigherconcentrationofthe
atmosphereoxygen.
Thus, part of the metal below the water acts as anode and undergoes corrosion.
Waterline Corrosion
31
MATRUSRI
ENGINEERING COLLEGE
The part above the water line is free from corrosion.
A distinct brown line is formed just blow the water line due to the deposition of
rust.
•At anode: Fe →Fe
2+
+ 2e
-
(Oxidation)
•At cathode: ½ O
2+ H
2O + 2e
-
→2 OH
-
(Reduction)
32
MATRUSRI
ENGINEERING COLLEGE
Waterline Corrosion
rust.
•At anode: Fe →Fe
2+
+ 2e
-
(Oxidation)
•At cathode: ½ O
2+ H
2O + 2e
-
→2 OH
-
(Reduction)
32
MATRUSRI
ENGINEERING COLLEGE
Waterline Corrosion
QUIZ
1.Thecorrosionwhichoccursduetothedifferenceinoxygenconcentrationis
called
a)oxidationcorrosion b)differentialaerationcorrosion
c)galvaniccorrosion d)none
2.Thepartofthemetalbelowthewaterlineactsas___inwaterlinecorrosion
a)cathode b)anode c)electrolyted)none
3.Inwaterlinecorrosionthereactioninvolvedatcathodeis
a)absorptionofoxygen b)evolutionofhydrogen
c)evolutionofoxygen d)absorptionofhydrogen
4.Adistinctbrownlineisformed_______thewaterlineduetodepositionof
rust.
a)above b)below c)surfaceofwaterlined)none
33
MATRUSRI
ENGINEERING COLLEGE
1.Thecorrosionwhichoccursduetothedifferenceinoxygenconcentrationis
called
a)oxidationcorrosion b)differentialaerationcorrosion
c)galvaniccorrosion d)none
2.Thepartofthemetalbelowthewaterlineactsas___inwaterlinecorrosion
a)cathode b)anode c)electrolyted)none
3.Inwaterlinecorrosionthereactioninvolvedatcathodeis
a)absorptionofoxygen b)evolutionofhydrogen
c)evolutionofoxygen d)absorptionofhydrogen
4.Adistinctbrownlineisformed_______thewaterlineduetodepositionof
rust.
a)above b)below c)surfaceofwaterlined)none
33
MATRUSRI
ENGINEERING COLLEGE
Pittingcorrosionisalocalizedandacceleratedcorrosion,resultingin
theformationofpitsorpinholesaroundwhichthemetalisrelatively
un-attacked.
MODULE-5: PITTING CORROSION
34
MATRUSRI
ENGINEERING COLLEGE
Itischaracterizedbysmallanodicandlargecathodicareas,resultingin
acceleratedcorrosionattheanodicarea.
theformationofpitsorpinholesaroundwhichthemetalisrelatively
un-attacked.
MODULE-5: PITTING CORROSION
34
MATRUSRI
ENGINEERING COLLEGE
Itischaracterizedbysmallanodicandlargecathodicareas,resultingin
acceleratedcorrosionattheanodicarea.
Itisgenerallyinitiatedbythedepositionofextraneousmattersuchas
sand,scale,waterdrop,dustetc,
or
Duetothebreakdownorcrackingoftheprotectivefilmonmetal
surface.
Thisgivesrisetotheformationofsmallanodicandlargecathodic
areas.
Inthecorrectenvironment,thisproducescorrosioncurrent.
Itisanautocatalyticprocess,withtheinitiallyformedpitproduces
conditionswhicharebothstimulatingandnecessaryforthe
continuingactivityofthepit.
PITTING CORROSION
35
MATRUSRI
ENGINEERING COLLEGE
sand,scale,waterdrop,dustetc,
or
Duetothebreakdownorcrackingoftheprotectivefilmonmetal
surface.
Thisgivesrisetotheformationofsmallanodicandlargecathodic
areas.
Inthecorrectenvironment,thisproducescorrosioncurrent.
Itisanautocatalyticprocess,withtheinitiallyformedpitproduces
conditionswhicharebothstimulatingandnecessaryforthe
continuingactivityofthepit.
PITTING CORROSION
35
MATRUSRI
ENGINEERING COLLEGE
36
MATRUSRI
ENGINEERING COLLEGE
Themetalsurfacewhichiscoveredbythedrophaslowoxygen
concentrationandthusactsasananodeandsufferscorrosion.
TheuncoveredmetalsurfaceduetohighO
2concentrationactsas
cathode.
MATRUSRI
ENGINEERING COLLEGE
Themetalsurfacewhichiscoveredbythedrophaslowoxygen
concentrationandthusactsasananodeandsufferscorrosion.
TheuncoveredmetalsurfaceduetohighO
2concentrationactsas
cathode.
At anode: Fe →Fe
2+
+ 2e
-
(Oxidation)
At Cathode: ½ O
2+ H2O + 2e
-
→2 OH
-
(Reduction)
Oxidation
Fe
2+
+ 2OH
-
→Fe(OH)
2 →Fe(OH)
3
37
MATRUSRI
ENGINEERING COLLEGE
Oncethecorrosionproductisformed,itfurtherprovidestheconditionfor
differentialaerationbelowthecorrosionproductandthesurroundingmetal
parts.Thepitgrowsandultimatelymaycausefailureofmetal.
2+
+ 2e
-
(Oxidation)
At Cathode: ½ O
2+ H2O + 2e
-
→2 OH
-
(Reduction)
Oxidation
Fe
2+
+ 2OH
-
→Fe(OH)
2 →Fe(OH)
3
37
MATRUSRI
ENGINEERING COLLEGE
Oncethecorrosionproductisformed,itfurtherprovidestheconditionfor
differentialaerationbelowthecorrosionproductandthesurroundingmetal
parts.Thepitgrowsandultimatelymaycausefailureofmetal.
38
MATRUSRI
ENGINEERING COLLEGE
➢Pittingisoneofthemostdestructiveformsofcorrosion.
➢Itcausesequipmenttofailbecauseofperforationwithonlyasmall
percentweightlossoftheentirestructure.
➢Itisoftendifficulttodetectpitsbecauseoftheirsmallsizeandalso
becausepitsarecoveredwithcorrosionproducts.
➢Pittingisdangerousbecauseitislocalizedandintensecorrosion
andfailuresoftenoccurwithextremesuddenness.
➢Assuch,itisratherdifficulttoassesspreciselythelifeofmetal
componentundergoingpittingcorrosion.
MATRUSRI
ENGINEERING COLLEGE
➢Pittingisoneofthemostdestructiveformsofcorrosion.
➢Itcausesequipmenttofailbecauseofperforationwithonlyasmall
percentweightlossoftheentirestructure.
➢Itisoftendifficulttodetectpitsbecauseoftheirsmallsizeandalso
becausepitsarecoveredwithcorrosionproducts.
➢Pittingisdangerousbecauseitislocalizedandintensecorrosion
andfailuresoftenoccurwithextremesuddenness.
➢Assuch,itisratherdifficulttoassesspreciselythelifeofmetal
componentundergoingpittingcorrosion.
QUIZ
1.Which of the following is most destructive type of corrosion?
a) galvanic corrosion b) waterline corrosion
c) pitting corrosion d) none
2. Which of the following type corrosion is an autocatalytic process?
a) pitting corrosion b) oxidation corrosion
c) waterline corrosiond) liquid metal corrosion
3. It is difficult to detect the pitting corrosion because
a) pits are small in sizeb) pits are covered with rust
c) small % of weight loss d) all the above
4. Which of the following corrosion reaction involves absorption of oxygen at
cathode?
a) waterline corrosionb) differential aeration corrosion
c) pitting corrosion d) all the above
39
MATRUSRI
ENGINEERING COLLEGE
1.Which of the following is most destructive type of corrosion?
a) galvanic corrosion b) waterline corrosion
c) pitting corrosion d) none
2. Which of the following type corrosion is an autocatalytic process?
a) pitting corrosion b) oxidation corrosion
c) waterline corrosiond) liquid metal corrosion
3. It is difficult to detect the pitting corrosion because
a) pits are small in sizeb) pits are covered with rust
c) small % of weight loss d) all the above
4. Which of the following corrosion reaction involves absorption of oxygen at
cathode?
a) waterline corrosionb) differential aeration corrosion
c) pitting corrosion d) all the above
39
MATRUSRI
ENGINEERING COLLEGE
1. Nature of Metal:
i) Position of metal in the Galvanic series
ii) Relative areas of anode and cathodes
iii) Overvoltage
iV) Purity of metal
v) Nature of surface oxide film
2. Nature of Environment:
i) Temperature
ii) Humidity
iii) pH
MODULE-6: FACTORS AFFECTING THE RATE OF CORROSION
40
MATRUSRI
ENGINEERING COLLEGE
i) Position of metal in the Galvanic series
ii) Relative areas of anode and cathodes
iii) Overvoltage
iV) Purity of metal
v) Nature of surface oxide film
2. Nature of Environment:
i) Temperature
ii) Humidity
iii) pH
MODULE-6: FACTORS AFFECTING THE RATE OF CORROSION
40
MATRUSRI
ENGINEERING COLLEGE
NATURE OF METAL
41
MATRUSRI
ENGINEERING COLLEGE
PositionofmetalintheGalvanicseries:Whenthemetalishigherupinthe
galvanicseries,greateristheoxidationpotential.Thus,greaterisitstendencyto
becomeanodicandhencegreateristherateofcorrosion.Whentwometalsare
inelectricalcontact,greateristhedifferenceintheirpositionsinthe
electrochemicalseries,fasteristhecorrosionofanodicmetal.
41
MATRUSRI
ENGINEERING COLLEGE
PositionofmetalintheGalvanicseries:Whenthemetalishigherupinthe
galvanicseries,greateristheoxidationpotential.Thus,greaterisitstendencyto
becomeanodicandhencegreateristherateofcorrosion.Whentwometalsare
inelectricalcontact,greateristhedifferenceintheirpositionsinthe
electrochemicalseries,fasteristhecorrosionofanodicmetal.
42
MATRUSRI
ENGINEERING COLLEGENATURE OF METAL
Relativeareasofanodeandcathodes:Corrosionismorerapidandsevere,and
highlylocalized,iftheanodicareaissmall,becausethecurrentdensityata
smalleranodicareaismuchgreater,andthedemandforelectronsbycathodic
areascanbemetbysmalleranodicareasonlybyundergoingcorrosionmore
briskly.
MATRUSRI
ENGINEERING COLLEGENATURE OF METAL
Relativeareasofanodeandcathodes:Corrosionismorerapidandsevere,and
highlylocalized,iftheanodicareaissmall,becausethecurrentdensityata
smalleranodicareaismuchgreater,andthedemandforelectronsbycathodic
areascanbemetbysmalleranodicareasonlybyundergoingcorrosionmore
briskly.
43
MATRUSRI
ENGINEERING COLLEGE
NATURE OF METAL
Overvoltage:Whenametalwhichoccupiesahighpositioningalvanic
series,sayzincisplacedin1NH
2SO
4,itundergoescorrosionformingafilm
andevolvinghydrogengas,theinitialrateofreactionisquiteslow,because
ofhighovervoltageofzincmetal,whichreducestheeffectiveelectrode
potential(=0.70V)toasmallvalue.
However,ifafewdropsofcoppersulphateareadded,thecorrosionrateof
zincisaccelerated,becausesomecoppergetsdepositedonthezincmetal,
formingminutecathodes,wherethehydrogenovervoltageisonly0.33V.
Thus,reductioninovervoltageofthecorrodingmetalacceleratesthe
corrosionrate.
MATRUSRI
ENGINEERING COLLEGE
NATURE OF METAL
Overvoltage:Whenametalwhichoccupiesahighpositioningalvanic
series,sayzincisplacedin1NH
2SO
4,itundergoescorrosionformingafilm
andevolvinghydrogengas,theinitialrateofreactionisquiteslow,because
ofhighovervoltageofzincmetal,whichreducestheeffectiveelectrode
potential(=0.70V)toasmallvalue.
However,ifafewdropsofcoppersulphateareadded,thecorrosionrateof
zincisaccelerated,becausesomecoppergetsdepositedonthezincmetal,
formingminutecathodes,wherethehydrogenovervoltageisonly0.33V.
Thus,reductioninovervoltageofthecorrodingmetalacceleratesthe
corrosionrate.
44
MATRUSRI
ENGINEERING COLLEGE
NATURE OF METAL
Purityofmetal:Impuritiesinametalcauseheterogeneityandformtiny
electrochemicalcellsattheexposedparts,andtheanodicpartsgetcorroded.
Forexample,zincmetalcontainingimpuritysuchasPborFeundergoes
corrosionduetoformationoflocalelectrochemicalcells.Therateandextentof
corrosionincreasewiththeincreasingexposureandextentoftheimpurities.
Natureofsurfaceoxidefilm:Inaeratedatmosphere,practicallyallmetalsget
coveredwithathinsurfacefilmofmetaloxide.Theratioofthevolumesofthe
metaloxidetothemetalisknownasspecificvolumeratio.Greaterthespecific
volumeratio,lesseristheoxidationcorrosionrate.
Forexample,thespecificvolumeratiosofNi,CrandWare1.6,2.0and3.6
respectively.Consequently,therateofoxidationoftungstenisleast,evenat
elevatedtemperatures.
MATRUSRI
ENGINEERING COLLEGE
NATURE OF METAL
Purityofmetal:Impuritiesinametalcauseheterogeneityandformtiny
electrochemicalcellsattheexposedparts,andtheanodicpartsgetcorroded.
Forexample,zincmetalcontainingimpuritysuchasPborFeundergoes
corrosionduetoformationoflocalelectrochemicalcells.Therateandextentof
corrosionincreasewiththeincreasingexposureandextentoftheimpurities.
Natureofsurfaceoxidefilm:Inaeratedatmosphere,practicallyallmetalsget
coveredwithathinsurfacefilmofmetaloxide.Theratioofthevolumesofthe
metaloxidetothemetalisknownasspecificvolumeratio.Greaterthespecific
volumeratio,lesseristheoxidationcorrosionrate.
Forexample,thespecificvolumeratiosofNi,CrandWare1.6,2.0and3.6
respectively.Consequently,therateofoxidationoftungstenisleast,evenat
elevatedtemperatures.
45
MATRUSRI
ENGINEERING COLLEGE
NATURE OF ENVIRONMENT
Temperature:Therateofachemicalreaction,ingeneral,increaseswithrisein
temperature.Corrosionprocessisonesuchchemicalreaction.Therefore,the
rateofcorrosionincreasesasthetemperatureincreases.Increasein
temperatureincreasestheconductanceofthecorrosionmedium,whichalso
contributestotheincreaseinrateofcorrosion.
Humidity:Thegreaterishumidity,thegreateristherateandextentof
corrosion.Thisisduetothefactthatthemoistureorvapourspresentin
atmosphereactsasasolventforO
2,H
2S,SO
2andNaCletc.tofurnishthe
electrolyteessentialforsettingupanelectrochemicalcell.
pH:Ingeneral,lowerthepHofthecorrosionmedium,higheristhecorrosion
rate.However,somemetalslikeAl,Znundergofastcorrosioninhighlyalkaline
solution.ThepHofthesolutionsalsodecidesthetypeofcathodicreaction.
MATRUSRI
ENGINEERING COLLEGE
NATURE OF ENVIRONMENT
Temperature:Therateofachemicalreaction,ingeneral,increaseswithrisein
temperature.Corrosionprocessisonesuchchemicalreaction.Therefore,the
rateofcorrosionincreasesasthetemperatureincreases.Increasein
temperatureincreasestheconductanceofthecorrosionmedium,whichalso
contributestotheincreaseinrateofcorrosion.
Humidity:Thegreaterishumidity,thegreateristherateandextentof
corrosion.Thisisduetothefactthatthemoistureorvapourspresentin
atmosphereactsasasolventforO
2,H
2S,SO
2andNaCletc.tofurnishthe
electrolyteessentialforsettingupanelectrochemicalcell.
pH:Ingeneral,lowerthepHofthecorrosionmedium,higheristhecorrosion
rate.However,somemetalslikeAl,Znundergofastcorrosioninhighlyalkaline
solution.ThepHofthesolutionsalsodecidesthetypeofcathodicreaction.
QUIZ
1.The rate of corrosion is more when
a) Metal is higher up in galvanic series b) Rise in temperature
c) Small anode & large cathodicareasd) All the above
2. Which of the following factor reduce rate of corrosion
a) overvoltage b) stable oxide layer
c) absence of humidityd) all the above
3. Rate of corrosion of anodic region is directly proportional to the
a) cathode area b) anode area
c) product of anode & cathode areasd) sum of anode & cathode areas
46
MATRUSRI
ENGINEERING COLLEGE
1.The rate of corrosion is more when
a) Metal is higher up in galvanic series b) Rise in temperature
c) Small anode & large cathodicareasd) All the above
2. Which of the following factor reduce rate of corrosion
a) overvoltage b) stable oxide layer
c) absence of humidityd) all the above
3. Rate of corrosion of anodic region is directly proportional to the
a) cathode area b) anode area
c) product of anode & cathode areasd) sum of anode & cathode areas
46
MATRUSRI
ENGINEERING COLLEGE
Theprincipleinvolvedinthismethodofprotectionistoforcethemetaltobe
protectedtobehavelikeacathode,therebycorrosiondoesnotoccur.
Therearetwotypesofcathodicprotection.
a)Sacrificialanodemethod.
b)Impressedcurrentmethod.
47
MATRUSRI
ENGINEERING COLLEGE
MODULE-7: CATHODICPROTECTION
protectedtobehavelikeacathode,therebycorrosiondoesnotoccur.
Therearetwotypesofcathodicprotection.
a)Sacrificialanodemethod.
b)Impressedcurrentmethod.
47
MATRUSRI
ENGINEERING COLLEGE
MODULE-7: CATHODICPROTECTION
In this method of protection, the metallic structure to be protected is connected
to more anodic metal through a wire.
So that all the corrosion is concentrated at the more anodic metal.
Sacrificial Anodic Protection
48
MATRUSRI
ENGINEERING COLLEGE
to more anodic metal through a wire.
So that all the corrosion is concentrated at the more anodic metal.
Sacrificial Anodic Protection
48
MATRUSRI
ENGINEERING COLLEGE
Themoreanodicmetalitselfgetscorrodedslowly;whiletheparentstructureis
protected.
Themoreactivemetalsoemployediscalled“sacrificialanode”.
Thecorrodedsacrificialanodeblockisreplacedbyafreshone,when
consumedcompletely.
Metals commonly used as sacrificial anodes are Zn, Al, Mg and their alloys.
Mg is used in high resistivity electrolytes such as soils due to its most negative
potential and it can provide highest current output.
49
MATRUSRI
ENGINEERING COLLEGE
Sacrificial Anodic Protection
protected.
Themoreactivemetalsoemployediscalled“sacrificialanode”.
Thecorrodedsacrificialanodeblockisreplacedbyafreshone,when
consumedcompletely.
Metals commonly used as sacrificial anodes are Zn, Al, Mg and their alloys.
Mg is used in high resistivity electrolytes such as soils due to its most negative
potential and it can provide highest current output.
49
MATRUSRI
ENGINEERING COLLEGE
Sacrificial Anodic Protection
Examples:
Ship'ssteelhulls
Offshoredrillingplatforms
Oilandgasunderseapipelines
Containersusedtostorewaterandotherliquids
areprotectedbythismethod.
50
MATRUSRI
ENGINEERING COLLEGE
Ship'ssteelhulls
Offshoredrillingplatforms
Oilandgasunderseapipelines
Containersusedtostorewaterandotherliquids
areprotectedbythismethod.
50
MATRUSRI
ENGINEERING COLLEGE
Inthismethodcurrentfromanexternalsourceisimpressedintheopposite
directiontonullifythecorrosioncurrent.
Thus,theanodiccorrodingmetalbecomescathodicandprotectedfrom
corrosion.
51
MATRUSRI
ENGINEERING COLLEGE
Impressed Current Method
directiontonullifythecorrosioncurrent.
Thus,theanodiccorrodingmetalbecomescathodicandprotectedfrom
corrosion.
51
MATRUSRI
ENGINEERING COLLEGE
Impressed Current Method
Theanodemaybeeitheraninertmetaloronewhichdeterioratesandwillhave
tobereplacedperiodically.
Thecommonlyusedanodicmaterialsaregraphite,carbon,stainlesssteel,
scrapiron,highsilicaironandplatinum.
Theanodeisburiedinbackfillsuchasgypsumtoincreasetheelectrical
contactbetweenitselfandthesurroundingsoil.
Thisprotectionmethodisusefulwhenelectrolyteresistivityandcurrent
requirementsarehigh.
Itiswellsuitedforlargestructuresandlong-termapplications.
Applications:This protection technique is employed in the case of open water box
coolers, water tanks, buried pipe-lines, marine pipes etc.
52
MATRUSRI
ENGINEERING COLLEGE
Impressed Current Method
tobereplacedperiodically.
Thecommonlyusedanodicmaterialsaregraphite,carbon,stainlesssteel,
scrapiron,highsilicaironandplatinum.
Theanodeisburiedinbackfillsuchasgypsumtoincreasetheelectrical
contactbetweenitselfandthesurroundingsoil.
Thisprotectionmethodisusefulwhenelectrolyteresistivityandcurrent
requirementsarehigh.
Itiswellsuitedforlargestructuresandlong-termapplications.
Applications:This protection technique is employed in the case of open water box
coolers, water tanks, buried pipe-lines, marine pipes etc.
52
MATRUSRI
ENGINEERING COLLEGE
Impressed Current Method
QUIZ
1.In the cathodicprotection, the metal which is wanted to be protected is
a) forced to behave like an anode b) forced to behave like a cathode
c) forced to behave like a conductord) none
2. In the sacrificial anodic protection metal the base metal is connected to a
_______ through a wire.
a) more active metal b) less active metal
c) cathodicmetal d) none
3. Which of the following metals can provide cathodicprotection to Fe?
a) Al & Cub) Al & Zn c) Zn & Cu d) Cu & Ni
4. The method in which corrosion current is nullified using an external source of
emfis called as
a) impressed current methodb) sacrificial anodic protection
c) sacrificial cathodicprotectiond) none
53
MATRUSRI
ENGINEERING COLLEGE
1.In the cathodicprotection, the metal which is wanted to be protected is
a) forced to behave like an anode b) forced to behave like a cathode
c) forced to behave like a conductord) none
2. In the sacrificial anodic protection metal the base metal is connected to a
_______ through a wire.
a) more active metal b) less active metal
c) cathodicmetal d) none
3. Which of the following metals can provide cathodicprotection to Fe?
a) Al & Cub) Al & Zn c) Zn & Cu d) Cu & Ni
4. The method in which corrosion current is nullified using an external source of
emfis called as
a) impressed current methodb) sacrificial anodic protection
c) sacrificial cathodicprotectiond) none
53
MATRUSRI
ENGINEERING COLLEGE
MODULE-8: HOT DIPPING -GALVANIZING
54
MATRUSRI
ENGINEERING COLLEGE
HotdippingisamethodofcoatingalowmeltingmetalsuchasZn
(m.p.=419
o
C),Sn(m.p.=232
o
C)Pb,Al,etc.,oniron,steelandcopperwhich
haverelativelyhighermeltingpoints.
54
MATRUSRI
ENGINEERING COLLEGE
HotdippingisamethodofcoatingalowmeltingmetalsuchasZn
(m.p.=419
o
C),Sn(m.p.=232
o
C)Pb,Al,etc.,oniron,steelandcopperwhich
haverelativelyhighermeltingpoints.
HOT DIPPING
55
MATRUSRI
ENGINEERING COLLEGE
Thebasemetalisdippedinamoltenbathofthecoatingmetalwhichiscovered
byamoltenfluxlayer.
Fluxcleansthebasemetalsurfaceandpreventstheoxidationofthecoating
metal.
Forgoodadhesionofthecoatingmetalonthesurfaceofbasemetal,thebase
metalsurfacemustbeveryclean.
ThemostcommonlyusedhotdippingmethodsareGalvanizingandTinning.
55
MATRUSRI
ENGINEERING COLLEGE
Thebasemetalisdippedinamoltenbathofthecoatingmetalwhichiscovered
byamoltenfluxlayer.
Fluxcleansthebasemetalsurfaceandpreventstheoxidationofthecoating
metal.
Forgoodadhesionofthecoatingmetalonthesurfaceofbasemetal,thebase
metalsurfacemustbeveryclean.
ThemostcommonlyusedhotdippingmethodsareGalvanizingandTinning.
GalvanizingisaprocessofcoatingironorsteelsheetswithathincoatofZnto
preventthemfromrusting.
GALVANIZING
56
MATRUSRI
ENGINEERING COLLEGE
preventthemfromrusting.
GALVANIZING
56
MATRUSRI
ENGINEERING COLLEGE
Thebasemetalironorsteelsheetiscleanedbyacidpicklingmethodwith
dil.H
2SO
4for15-20minutesat60-90
o
C.
Thesheetisthenwashedwellanddried.Itisdippedinabathofmoltenzinc
maintainedat425-435
o
C.
Thesurfaceofthebathiskeptcoveredwithammoniumchloridefluxtoprevent
oxideformation.
ThesheetistakenoutandexcessZnisremovedbypassingitbetweenapair
ofhotrollers.
Thenthesheetissubjectedtoannealingprocessat650
o
Candcooledslowly.
Analloyofironandzincwereformedatthejunctionofthebasemetaland
coatingmetal.
GALVANIZING PROCESS
57
MATRUSRI
ENGINEERING COLLEGE
dil.H
2SO
4for15-20minutesat60-90
o
C.
Thesheetisthenwashedwellanddried.Itisdippedinabathofmoltenzinc
maintainedat425-435
o
C.
Thesurfaceofthebathiskeptcoveredwithammoniumchloridefluxtoprevent
oxideformation.
ThesheetistakenoutandexcessZnisremovedbypassingitbetweenapair
ofhotrollers.
Thenthesheetissubjectedtoannealingprocessat650
o
Candcooledslowly.
Analloyofironandzincwereformedatthejunctionofthebasemetaland
coatingmetal.
GALVANIZING PROCESS
57
MATRUSRI
ENGINEERING COLLEGE
Applications:Itismostlyusedtoprotectironusedforroofingsheets,wires,
pipes,nails,bolts,screws,bucketsandtubes.
Galvanizingutensilscannotbeusedforpreparingandstoringfoodstuffs
especiallyacidicinnature,becausezincdissolvestoformhighlytoxicor
poisonouscompounds.
58
MATRUSRI
ENGINEERING COLLEGE
pipes,nails,bolts,screws,bucketsandtubes.
Galvanizingutensilscannotbeusedforpreparingandstoringfoodstuffs
especiallyacidicinnature,becausezincdissolvestoformhighlytoxicor
poisonouscompounds.
58
MATRUSRI
ENGINEERING COLLEGE
QUIZ
1.Coating a low melting metal on a relatively high melting metal surface is
called___
a) Hot dipping b) Cathodicprotection
c) Anodic protection d) none
2. The process of coating Fe or Steel with a zinc coating metal is called
a) tinning b) galvanizing
c) cladding d) none
3.Thesurfaceofthemoltenbathiscoveredwithammoniumchloridefluxto
prevent______
a)carbonateformation b)oxideformation
c)sulphideformation d)none
4.Thegalvanizingproductscannotbeusedfor
a)rooftop b)foodstorage
c)buckets d)all
59
MATRUSRI
ENGINEERING COLLEGE
1.Coating a low melting metal on a relatively high melting metal surface is
called___
a) Hot dipping b) Cathodicprotection
c) Anodic protection d) none
2. The process of coating Fe or Steel with a zinc coating metal is called
a) tinning b) galvanizing
c) cladding d) none
3.Thesurfaceofthemoltenbathiscoveredwithammoniumchloridefluxto
prevent______
a)carbonateformation b)oxideformation
c)sulphideformation d)none
4.Thegalvanizingproductscannotbeusedfor
a)rooftop b)foodstorage
c)buckets d)all
59
MATRUSRI
ENGINEERING COLLEGE
MODULE-9: WATER CHEMISTRY
60
Hardnessofwater:Waterwhichdoesnotproducelatherwithsoapsolution
readilybutformsawhitecurdiscalledhardwater.
Hardnessinwateristhatcharacteristic,which“preventsthelatheringofsoap”.
Thisisduetopresenceofcertainsaltsofcalcium,magnesiumandotherheavy
metalsdissolvedinit.
Whenhardwateristreatedwithsoapdoesnotproducelatherandformsawhite
scumorprecipitateduetotheformationofinsolublesoapsofcalciumand
magnesium.
2C
17
H
35
COONa+CaCl
2
→(C
17
H
35
COO)
2
Ca+2NaCl
SodiumstearateHardness Calciumstearate
Soap (insoluble)
2C
17
H
35
COONa+MgSO
4
→(C
17
H
35
COO)
2
Mg+Na
2
SO
4
MATRUSRI
ENGINEERING COLLEGE
60
Hardnessofwater:Waterwhichdoesnotproducelatherwithsoapsolution
readilybutformsawhitecurdiscalledhardwater.
Hardnessinwateristhatcharacteristic,which“preventsthelatheringofsoap”.
Thisisduetopresenceofcertainsaltsofcalcium,magnesiumandotherheavy
metalsdissolvedinit.
Whenhardwateristreatedwithsoapdoesnotproducelatherandformsawhite
scumorprecipitateduetotheformationofinsolublesoapsofcalciumand
magnesium.
2C
17
H
35
COONa+CaCl
2
→(C
17
H
35
COO)
2
Ca+2NaCl
SodiumstearateHardness Calciumstearate
Soap (insoluble)
2C
17
H
35
COONa+MgSO
4
→(C
17
H
35
COO)
2
Mg+Na
2
SO
4
MATRUSRI
ENGINEERING COLLEGE
TYPES OF HARDNESS
Temporaryhardness(bicarbonatehardness):Itiscausedbythepresence
ofdissolvedbicarbonatesofcalcium,magnesiumandotherheavymetals
andcarbonateofiron.
Temporaryhardnesscanberemovedbyboilingofwater.
Bicarbonatesaredecomposedintoinsolublecarbonatesorhydroxides,which
aredepositedasacrustatthebottomofvesselonboilingthewater.
Heat
Ca(HCO
3)
2→ CaCO
3+H
2O+CO
2
Calciumbicarbonate Calciumcarbonate
(insoluble)
Mg(HCO
3)
2→ Mg(OH)
2+2CO
2
MagnesiumbicarbonateMagnesiumhydroxide
61
MATRUSRI
ENGINEERING COLLEGE
Temporaryhardness(bicarbonatehardness):Itiscausedbythepresence
ofdissolvedbicarbonatesofcalcium,magnesiumandotherheavymetals
andcarbonateofiron.
Temporaryhardnesscanberemovedbyboilingofwater.
Bicarbonatesaredecomposedintoinsolublecarbonatesorhydroxides,which
aredepositedasacrustatthebottomofvesselonboilingthewater.
Heat
Ca(HCO
3)
2→ CaCO
3+H
2O+CO
2
Calciumbicarbonate Calciumcarbonate
(insoluble)
Mg(HCO
3)
2→ Mg(OH)
2+2CO
2
MagnesiumbicarbonateMagnesiumhydroxide
61
MATRUSRI
ENGINEERING COLLEGE
TYPES OF HARDNESS
Permanenthardness(Non-carbonatehardness):Itisduetothepresenceof
chloridesandsulphatesofcalcium,magnesium,ironandotherheavy
metals.
Unliketemporaryhardness,permanenthardnessisnotdestroyedonboiling.
62
MATRUSRI
ENGINEERING COLLEGE
Permanenthardness(Non-carbonatehardness):Itisduetothepresenceof
chloridesandsulphatesofcalcium,magnesium,ironandotherheavy
metals.
Unliketemporaryhardness,permanenthardnessisnotdestroyedonboiling.
62
MATRUSRI
ENGINEERING COLLEGE
63
Theconcentrationofhardnessandnon-hardnesssaltsisexpressedinterms
ofequivalentamountofCaCO
3.
Sincethismodepermitsthemultiplicationanddivisionofconcentrationwhen
required.
ThechoiceofCaCO
3
inparticularisdueto:
itsmolecularweightis100(equivalentweight=50)
itisthemostinsolublesaltthatcanbeprecipitatedinwatertreatment.
EQUIVALENTS OF CALCIUM CARBONATE
MATRUSRI
ENGINEERING COLLEGE
OR
The equivalents of CaCO3=
Mass of hardness producing substance
Molecular weight of hardness substance
X 100
The equivalents of CaCO3=
Mass of hardness producing substance
Equivalent weight of hardness substance
X 50
Theconcentrationofhardnessandnon-hardnesssaltsisexpressedinterms
ofequivalentamountofCaCO
3.
Sincethismodepermitsthemultiplicationanddivisionofconcentrationwhen
required.
ThechoiceofCaCO
3
inparticularisdueto:
itsmolecularweightis100(equivalentweight=50)
itisthemostinsolublesaltthatcanbeprecipitatedinwatertreatment.
EQUIVALENTS OF CALCIUM CARBONATE
MATRUSRI
ENGINEERING COLLEGE
OR
The equivalents of CaCO3=
Mass of hardness producing substance
Molecular weight of hardness substance
X 100
The equivalents of CaCO3=
Mass of hardness producing substance
Equivalent weight of hardness substance
X 50
64
Partspermillion(ppm):Itisthepartofcalciumcarbonateequivalent
hardnessper10
6
partsofwater.
i.e.1ppm=1partofCaCO
3eq.hardnessin10
6
partsofwater.
Milligramsperlitre(mg/L)isthenumberofmilligramsofCaCO
3equivalent
hardnesspresentperlitreofwater.
1mg/L=1mgofCaCO
3eq.hardnessin1Lofwater.
But,
1Lofwaterweighs=1kg=1000g=1000X1000mg=10
6
mg.
Therefore,1mg/L=1mgofCaCO
3eqper10
6
mgofwater.
=1partofCaCO
3eqper10
6
partsofwater
1mg/L=1ppm
UNITS OF HARDNESS
MATRUSRI
ENGINEERING COLLEGE
Partspermillion(ppm):Itisthepartofcalciumcarbonateequivalent
hardnessper10
6
partsofwater.
i.e.1ppm=1partofCaCO
3eq.hardnessin10
6
partsofwater.
Milligramsperlitre(mg/L)isthenumberofmilligramsofCaCO
3equivalent
hardnesspresentperlitreofwater.
1mg/L=1mgofCaCO
3eq.hardnessin1Lofwater.
But,
1Lofwaterweighs=1kg=1000g=1000X1000mg=10
6
mg.
Therefore,1mg/L=1mgofCaCO
3eqper10
6
mgofwater.
=1partofCaCO
3eqper10
6
partsofwater
1mg/L=1ppm
UNITS OF HARDNESS
MATRUSRI
ENGINEERING COLLEGE
65
Q1:Asampleofwatercontainsthefollowingimpurities:Ca(HCO
3)
2=14.6
mg/L,Mg(HCO
3)
2=30mg/L,MgCl
2=19mg/L,MgSO
4=36mg/L.Calculate
temporaryandpermanenthardnessinppm.
Solution:
Substance Weight(mg/L) GMW Eq. of CaCO
3
Ca(HCO
3)
2 14.6 162
Mg(HCO
3)
2 30 146
MgCl
2 19 95
MgSO
4 36 120
Temporary hardness (Ca(HCO
3)
2+ Mg(HCO
3)
2) = 9 + 20 = 29 mg/L
Permanent hardness (MgCl
2+ MgSO
4) = 20 + 30 = 50 mg/L
NUMERICAL PROBLEMS
MATRUSRI
ENGINEERING COLLEGE
Q1:Asampleofwatercontainsthefollowingimpurities:Ca(HCO
3)
2=14.6
mg/L,Mg(HCO
3)
2=30mg/L,MgCl
2=19mg/L,MgSO
4=36mg/L.Calculate
temporaryandpermanenthardnessinppm.
Solution:
Substance Weight(mg/L) GMW Eq. of CaCO
3
Ca(HCO
3)
2 14.6 162
Mg(HCO
3)
2 30 146
MgCl
2 19 95
MgSO
4 36 120
Temporary hardness (Ca(HCO
3)
2+ Mg(HCO
3)
2) = 9 + 20 = 29 mg/L
Permanent hardness (MgCl
2+ MgSO
4) = 20 + 30 = 50 mg/L
NUMERICAL PROBLEMS
MATRUSRI
ENGINEERING COLLEGE
66
Q2:AsampleofwateronanalysishasbeenfoundtocontainMg(HCO3)2=5.84
mg/L,Ca(HCO3)2=4.86mg/L,CaSO4=6.80mg/LandMgSO4=8.40mg/L.
NUMERICAL PROBLEMS
MATRUSRI
ENGINEERING COLLEGE
Solution:
Substance Mass (mg/L) GMW GEW CaCO3equivalents
Mg(HCO3)2 5.84 146 73 = x 50 = 4 mg/L
5.84
73
Ca(HCO3)2 4.86 162 81 = x 50 = 3 mg/L
4.86
81
CaSO4 6.80 136 68 = x 50 = 5 mg/L
6.80
68
MgSO4 8.40 120 60 = x 50 = 7 mg/L
8.40
60
Q2:AsampleofwateronanalysishasbeenfoundtocontainMg(HCO3)2=5.84
mg/L,Ca(HCO3)2=4.86mg/L,CaSO4=6.80mg/LandMgSO4=8.40mg/L.
NUMERICAL PROBLEMS
MATRUSRI
ENGINEERING COLLEGE
Solution:
Substance Mass (mg/L) GMW GEW CaCO3equivalents
Mg(HCO3)2 5.84 146 73 = x 50 = 4 mg/L
5.84
73
Ca(HCO3)2 4.86 162 81 = x 50 = 3 mg/L
4.86
81
CaSO4 6.80 136 68 = x 50 = 5 mg/L
6.80
68
MgSO4 8.40 120 60 = x 50 = 7 mg/L
8.40
60
67
NUMERICAL PROBLEMS
MATRUSRI
ENGINEERING COLLEGE
Permanent hardness is due to CaSO4and MgSO4:
= 5 + 7 = 12 mg/L or ppm
Total hardness = 4 + 3 + 5 +7 = 19 mg/L or ppm
Temporary hardness is due to Mg(HCO3)2and Ca(HCO3)2:
= 4 + 3 = 7 mg/L or ppm
NUMERICAL PROBLEMS
MATRUSRI
ENGINEERING COLLEGE
Permanent hardness is due to CaSO4and MgSO4:
= 5 + 7 = 12 mg/L or ppm
Total hardness = 4 + 3 + 5 +7 = 19 mg/L or ppm
Temporary hardness is due to Mg(HCO3)2and Ca(HCO3)2:
= 4 + 3 = 7 mg/L or ppm
QUIZ
1.The phenomenon of prevention of lathering of soap in water is called
a) softness b) hardness
c) turbidity d) none
2. Hardness in water is mainly caused due to presence of _______
a) salts of Ca & Mg b) Salts of Ca & Na
c) Salts of Mg & Na d) all the above
3. Hardness in water which cannot be removed on boiling is known as
a) temporary hardness b) permanent hardness
c) carbonate hardness d) a&c
4. Degree of hardness can be expressed in terms of
a) equivalents of CaCO3 b) equivalents of MgCO3
d) equivalents of Ca(HCO3)2d) equivalents of Mg(HCO3)2
68
MATRUSRI
ENGINEERING COLLEGE
1.The phenomenon of prevention of lathering of soap in water is called
a) softness b) hardness
c) turbidity d) none
2. Hardness in water is mainly caused due to presence of _______
a) salts of Ca & Mg b) Salts of Ca & Na
c) Salts of Mg & Na d) all the above
3. Hardness in water which cannot be removed on boiling is known as
a) temporary hardness b) permanent hardness
c) carbonate hardness d) a&c
4. Degree of hardness can be expressed in terms of
a) equivalents of CaCO3 b) equivalents of MgCO3
d) equivalents of Ca(HCO3)2d) equivalents of Mg(HCO3)2
68
MATRUSRI
ENGINEERING COLLEGE
69
MODULE-10: DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
This is a complexometrictitration in which EDTA is used as a complexingagent.
EDTAisahexadentateligandandformsstable
complexeswithmostofthemetalionsinthepH
range10.
PRINCPLE
MODULE-10: DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
This is a complexometrictitration in which EDTA is used as a complexingagent.
EDTAisahexadentateligandandformsstable
complexeswithmostofthemetalionsinthepH
range10.
PRINCPLE
70
DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
A buffer solution of NH
4Cl + NH
4OH is used to maintain the pH.
TodeterminetheequivalencepointEriochromeblack-T(EBT)isusedasan
indicator.
Free EBT in water
(Blue)
EBT in Hard water
( Wine Red)
DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
A buffer solution of NH
4Cl + NH
4OH is used to maintain the pH.
TodeterminetheequivalencepointEriochromeblack-T(EBT)isusedasan
indicator.
Free EBT in water
(Blue)
EBT in Hard water
( Wine Red)
71
DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
Itformsunstablewinered
coloredcomplexeswithCa
2+
&Mg
2+
ionsinthepHrange
10.
EDTAcombineswiththefreemetalions
inthebeginningandthemetalionsof
theindicatorcomplexattheend,
displacingtheindicator.
Titration against EDTA
Wine red Blue
DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
Itformsunstablewinered
coloredcomplexeswithCa
2+
&Mg
2+
ionsinthepHrange
10.
EDTAcombineswiththefreemetalions
inthebeginningandthemetalionsof
theindicatorcomplexattheend,
displacingtheindicator.
Titration against EDTA
Wine red Blue
72
DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
PREPARATION OF REAGENTS
Preparationofstandardhardwater:Dissolve1gofpureCaCO
3
inminimum
quantityofdil.HClandevaporateittodrynessonawaterbath.Dissolveitin
distilledwaterandmakeupto1L.EachmLofthissolutionthuscontains1mgof
CaCO
3
eqhardness.
PreparationofEDTAsolution:Dissolve4.0gofpureEDTAcrystalsandadd
0.1gofMgCl
2
toit.Makeupto1Lusingdistilledwater.
Preparationofindicator:Dissolve0.5gofEriochromeblack-Tin100mlof
alcohol.
Preparationofbuffersolution:Add67.5gofNH
4
Clto570mlofconcentrated
ammoniasolutionanddilutewithdistilledwaterto1L.
DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
PREPARATION OF REAGENTS
Preparationofstandardhardwater:Dissolve1gofpureCaCO
3
inminimum
quantityofdil.HClandevaporateittodrynessonawaterbath.Dissolveitin
distilledwaterandmakeupto1L.EachmLofthissolutionthuscontains1mgof
CaCO
3
eqhardness.
PreparationofEDTAsolution:Dissolve4.0gofpureEDTAcrystalsandadd
0.1gofMgCl
2
toit.Makeupto1Lusingdistilledwater.
Preparationofindicator:Dissolve0.5gofEriochromeblack-Tin100mlof
alcohol.
Preparationofbuffersolution:Add67.5gofNH
4
Clto570mlofconcentrated
ammoniasolutionanddilutewithdistilledwaterto1L.
73
DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
EXPERIMENTAL PROCEDURE
A.StandardizationofEDTAsolution:RinseandfilltheburettewithEDTA
solution.Pipetteout50mlofstandardhardwaterinaconicalflask.Add
10mlofbuffersolutionand3or4dropsofindicator,thecolorchangesto
winered.TitrateitagainstEDTAtillthecolorchangestoblue.Letthevolume
ofEDTAbeV
1ml.
50 ml of std. hard water = V
1ml of EDTA
i.e. 50 mg of CaCO
3eq. = V
1ml of EDTA
Hence, 1 ml of EDTA = mg of CaCO
3 eq.
50
V
1
DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
EXPERIMENTAL PROCEDURE
A.StandardizationofEDTAsolution:RinseandfilltheburettewithEDTA
solution.Pipetteout50mlofstandardhardwaterinaconicalflask.Add
10mlofbuffersolutionand3or4dropsofindicator,thecolorchangesto
winered.TitrateitagainstEDTAtillthecolorchangestoblue.Letthevolume
ofEDTAbeV
1ml.
50 ml of std. hard water = V
1ml of EDTA
i.e. 50 mg of CaCO
3eq. = V
1ml of EDTA
Hence, 1 ml of EDTA = mg of CaCO
3 eq.
50
V
1
74
DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
EXPERIMENTAL PROCEDURE
B.EstimationofTotalhardness:Pipetteout50mlofwatersampleina
conicalflask.Add10mlofbuffersolutionand3or4dropsofindicatortoit,the
colorchangestowinered.TitrateitagainstEDTAtillthecolorchangestoblue.
LetthevolumeofEDTAbeV
2ml.
50 ml of hard water = V
2ml of EDTA
Hence, 50 ml of hard water = x V
2 mg of CaCO
3 eq.
50
V
1
For 1000 ml of H.W = x V
2 mg of CaCO
3 eq.
1000
V
1
Total hardness = x 1000 ppm
V
2
V
1
DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
EXPERIMENTAL PROCEDURE
B.EstimationofTotalhardness:Pipetteout50mlofwatersampleina
conicalflask.Add10mlofbuffersolutionand3or4dropsofindicatortoit,the
colorchangestowinered.TitrateitagainstEDTAtillthecolorchangestoblue.
LetthevolumeofEDTAbeV
2ml.
50 ml of hard water = V
2ml of EDTA
Hence, 50 ml of hard water = x V
2 mg of CaCO
3 eq.
50
V
1
For 1000 ml of H.W = x V
2 mg of CaCO
3 eq.
1000
V
1
Total hardness = x 1000 ppm
V
2
V
1
75
DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
EXPERIMENTAL PROCEDURE
C.Estimationofpermanenthardness:Take250mlofthewatersampleina
largebeakerandboilittoonethirdofitsvolume,allthebicarbonatesare
precipitatedascarbonates.Filter,washtheprecipitatewithdistilledwater,and
collectthefiltrateandwashingsin250mlvolumetricflask.Makeupthevolume
usingdistilledwater.Thentitrate50mlofthiswaterasunderstandardization.
LetthevolumeofEDTAbeV
3ml.
50 ml of boiled water = V
3ml of EDTA
50
V
1
For 1000 ml of EDTA = x V
3 mg of CaCO
3 eq.
1000
V
1
Permanent hardness = x 1000 ppm
V
3
V
1
50 ml of boiled water = x V
3mg of CaCO
3 eq.
DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
EXPERIMENTAL PROCEDURE
C.Estimationofpermanenthardness:Take250mlofthewatersampleina
largebeakerandboilittoonethirdofitsvolume,allthebicarbonatesare
precipitatedascarbonates.Filter,washtheprecipitatewithdistilledwater,and
collectthefiltrateandwashingsin250mlvolumetricflask.Makeupthevolume
usingdistilledwater.Thentitrate50mlofthiswaterasunderstandardization.
LetthevolumeofEDTAbeV
3ml.
50 ml of boiled water = V
3ml of EDTA
50
V
1
For 1000 ml of EDTA = x V
3 mg of CaCO
3 eq.
1000
V
1
Permanent hardness = x 1000 ppm
V
3
V
1
50 ml of boiled water = x V
3mg of CaCO
3 eq.
76
DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
EXPERIMENTAL PROCEDURE
D. Temporary hardness: = [Total –Permanent] hardness
Temporary hardness = x 1000 ppm
V
2 -V
3
V
1
DETERMINATION OF HARDNESS BY EDTA METHOD
MATRUSRI
ENGINEERING COLLEGE
EXPERIMENTAL PROCEDURE
D. Temporary hardness: = [Total –Permanent] hardness
Temporary hardness = x 1000 ppm
V
2 -V
3
V
1
QUIZ
1.Determination of hardness by EDTA method is a type of
a) acid base titration b) redoxtitration
c) complexometrictitrationd) precipitation titrations
2. The composition of buffer solution used to maintain pH in EDTA method
a) NH4Cl + NaOH b) NH4Cl + NH4OH
c) NaCl+ NH4OH d) none
3. The colourof metal –indicator complex in EDTA method is
a) green b) blue
c) red d) wine red
4. The blue colourappears at the end point of EDTA method due to
a) free EBT b) Metal –EBT
c) Metal –EDTA d) free EDTA
77
MATRUSRI
ENGINEERING COLLEGE
1.Determination of hardness by EDTA method is a type of
a) acid base titration b) redoxtitration
c) complexometrictitrationd) precipitation titrations
2. The composition of buffer solution used to maintain pH in EDTA method
a) NH4Cl + NaOH b) NH4Cl + NH4OH
c) NaCl+ NH4OH d) none
3. The colourof metal –indicator complex in EDTA method is
a) green b) blue
c) red d) wine red
4. The blue colourappears at the end point of EDTA method due to
a) free EBT b) Metal –EBT
c) Metal –EDTA d) free EDTA
77
MATRUSRI
ENGINEERING COLLEGE
78
MATRUSRI
ENGINEERING COLLEGE
NUMERICAL PROBLEMS BASED ON EDTA METHOD
Q1:20mlofstandardhardwatercontaining15gofCaCO3perliter,required25ml
ofEDTAsolutionforendpoint.100mlofwatersamplerequired18mlofEDTA
solution;whilesamewaterafterboilingrequired12mlofEDTAsolution.Calculate
carbonateandnoncarbonatehardnessofwater.
Solution:
1000ml of standard hard water = 15 g of CaCO3eq. = 15 mg of CaCO3eq./ml
Now, 25 ml of EDTA solution = 20 ml of standard hard water
= 20 x 15 mg of CaCO3eq. = 300 mg of CaCO3eq.
Therefore, 1 ml of EDTA solution =
300
25
= 12 mg of CaCO3eq. hardness
MATRUSRI
ENGINEERING COLLEGE
NUMERICAL PROBLEMS BASED ON EDTA METHOD
Q1:20mlofstandardhardwatercontaining15gofCaCO3perliter,required25ml
ofEDTAsolutionforendpoint.100mlofwatersamplerequired18mlofEDTA
solution;whilesamewaterafterboilingrequired12mlofEDTAsolution.Calculate
carbonateandnoncarbonatehardnessofwater.
Solution:
1000ml of standard hard water = 15 g of CaCO3eq. = 15 mg of CaCO3eq./ml
Now, 25 ml of EDTA solution = 20 ml of standard hard water
= 20 x 15 mg of CaCO3eq. = 300 mg of CaCO3eq.
Therefore, 1 ml of EDTA solution =
300
25
= 12 mg of CaCO3eq. hardness
79
MATRUSRI
ENGINEERING COLLEGE
NUMERICAL PROBLEMS BASED ON EDTA METHOD
Calculation of Total hardness:
100ml of sample water = 18 ml of EDTA solution
= 18 x 12 mg of CaCO3eq.
= 216 mg of CaCO3eq.
For 1000ml of sample water = x 1000
216
100
Total hardness = 2160 ppm
= 2160 mg of CaCOeq. hardness
MATRUSRI
ENGINEERING COLLEGE
NUMERICAL PROBLEMS BASED ON EDTA METHOD
Calculation of Total hardness:
100ml of sample water = 18 ml of EDTA solution
= 18 x 12 mg of CaCO3eq.
= 216 mg of CaCO3eq.
For 1000ml of sample water = x 1000
216
100
Total hardness = 2160 ppm
= 2160 mg of CaCOeq. hardness
80
MATRUSRI
ENGINEERING COLLEGE
NUMERICAL PROBLEMS BASED ON EDTA METHOD
Calculation of non carbonate (permanent) hardness:
100ml of boiled water = 12 ml of EDTA solution
= 12 x 12 mg of CaCO3eq.
= 144 mg of CaCO3eq.
For 1000ml of boiled water = x 1000 = 1440 mg of CaCOeq. hardness
144
100
Permanent hardness = 1440 ppm
Carbonate (temporary) hardness = [Total –Permanent] hardness
= 2160 –1440 = 720 ppm
MATRUSRI
ENGINEERING COLLEGE
NUMERICAL PROBLEMS BASED ON EDTA METHOD
Calculation of non carbonate (permanent) hardness:
100ml of boiled water = 12 ml of EDTA solution
= 12 x 12 mg of CaCO3eq.
= 144 mg of CaCO3eq.
For 1000ml of boiled water = x 1000 = 1440 mg of CaCOeq. hardness
144
100
Permanent hardness = 1440 ppm
Carbonate (temporary) hardness = [Total –Permanent] hardness
= 2160 –1440 = 720 ppm
81
MATRUSRI
ENGINEERING COLLEGE
NUMERICAL PROBLEMS BASED ON EDTA METHOD
Q2:50mlofasamplewaterconsumed12mlof0.01MEDTAbeforeboilingand
10mlofthesameEDTAafterboiling.Calculatethetotalhardness,permanent
hardnessandtemporaryhardness.
Solution:
Since, EDTA reacts with Mg & Ca ions in 1:1 ratio;
1ml of 1 M EDTA = 100 mg of CaCO3eq.
i.e. 1 ml of 0.01 M EDTA = 1 mg of CaCO3 eq.
Calculation of Total hardness:
50 ml of sample water = 12 ml of 0.01 M EDTA
= 12 x 1 = 12 mg of CaCO3eq.
For 1000 ml of sample water = x 1000 = 240 mg of CaCO3eq.
12
50
Total hardness = 240 ppm
MATRUSRI
ENGINEERING COLLEGE
NUMERICAL PROBLEMS BASED ON EDTA METHOD
Q2:50mlofasamplewaterconsumed12mlof0.01MEDTAbeforeboilingand
10mlofthesameEDTAafterboiling.Calculatethetotalhardness,permanent
hardnessandtemporaryhardness.
Solution:
Since, EDTA reacts with Mg & Ca ions in 1:1 ratio;
1ml of 1 M EDTA = 100 mg of CaCO3eq.
i.e. 1 ml of 0.01 M EDTA = 1 mg of CaCO3 eq.
Calculation of Total hardness:
50 ml of sample water = 12 ml of 0.01 M EDTA
= 12 x 1 = 12 mg of CaCO3eq.
For 1000 ml of sample water = x 1000 = 240 mg of CaCO3eq.
12
50
Total hardness = 240 ppm
82
MATRUSRI
ENGINEERING COLLEGE
NUMERICAL PROBLEMS BASED ON EDTA METHOD
Calculation of Permanent hardness:
50 ml of boiled water = 10 ml of 0.01 M EDTA
= 10 x 1 = 10 mg of CaCO3eq.
For 1000 ml of sample water = x 1000 = 200 mg of CaCO3eq.
10
50
Permanent hardness = 200 ppm
Temporary hardness = [Total –Permanent] hardness
= 240 –200 = 40 ppm
MATRUSRI
ENGINEERING COLLEGE
NUMERICAL PROBLEMS BASED ON EDTA METHOD
Calculation of Permanent hardness:
50 ml of boiled water = 10 ml of 0.01 M EDTA
= 10 x 1 = 10 mg of CaCO3eq.
For 1000 ml of sample water = x 1000 = 200 mg of CaCO3eq.
10
50
Permanent hardness = 200 ppm
Temporary hardness = [Total –Permanent] hardness
= 240 –200 = 40 ppm
83
MODULE-11: ALKALINITY
MATRUSRI
ENGINEERING COLLEGE
PRINCPLE
Alkalinityofwaterismeasureofacid-neutralizingability.
Itisattributedtothepresenceofthecausticalkalinity(OH
-
andCO
3
2-
)and
temporaryhardness(HCO
3
-
).
Thesecanbeestimatedseparatelybytitrationagainstacid,using
phenolphthaleinandmethylorangeasindicators.
1.[OH
-
] + [H
+
] →H
2
O
2. [CO
3
2-
] + [H
+
] →[HCO
3
-
]
3. [HCO
3
-
] + [H
+
] →H
2
O + CO
2
P
M
MODULE-11: ALKALINITY
MATRUSRI
ENGINEERING COLLEGE
PRINCPLE
Alkalinityofwaterismeasureofacid-neutralizingability.
Itisattributedtothepresenceofthecausticalkalinity(OH
-
andCO
3
2-
)and
temporaryhardness(HCO
3
-
).
Thesecanbeestimatedseparatelybytitrationagainstacid,using
phenolphthaleinandmethylorangeasindicators.
1.[OH
-
] + [H
+
] →H
2
O
2. [CO
3
2-
] + [H
+
] →[HCO
3
-
]
3. [HCO
3
-
] + [H
+
] →H
2
O + CO
2
P
M
84
ALKALINITY
MATRUSRI
ENGINEERING COLLEGE
The possible combinations of ions causing alkalinity in water are:
➢OH
-
only or
➢CO
3
2-
only or
➢HCO
3
-
only or
➢OH
-
& CO
3
2-
together or
➢CO
3
2-
& HCO
3
-
together
OH
-
& HCO
3
-
ions cannot exist together in water.
OH
-
+ HCO
3
-
→CO
3
2-
+ H
2
O
Onthebasisofsamereasoning,allthethreeions(OH
-
,CO
3
2-
and
HCO
3
-
)cannotexisttogether.
ALKALINITY
MATRUSRI
ENGINEERING COLLEGE
The possible combinations of ions causing alkalinity in water are:
➢OH
-
only or
➢CO
3
2-
only or
➢HCO
3
-
only or
➢OH
-
& CO
3
2-
together or
➢CO
3
2-
& HCO
3
-
together
OH
-
& HCO
3
-
ions cannot exist together in water.
OH
-
+ HCO
3
-
→CO
3
2-
+ H
2
O
Onthebasisofsamereasoning,allthethreeions(OH
-
,CO
3
2-
and
HCO
3
-
)cannotexisttogether.
85
ALKALINITY
MATRUSRI
ENGINEERING COLLEGE
COLOURPROFILEOFINDICATORS
PHENALPTHALEIN
pH = 0 –8.2pH = 8.2 -10
METHYL ORANGE
pH = 2 –4.4pH = above 4.4
ALKALINITY
MATRUSRI
ENGINEERING COLLEGE
COLOURPROFILEOFINDICATORS
PHENALPTHALEIN
pH = 0 –8.2pH = 8.2 -10
METHYL ORANGE
pH = 2 –4.4pH = above 4.4
86
ALKALINITY
MATRUSRI
ENGINEERING COLLEGE
Experimental Procedure
Pipetteout100mlwatersampleinacleanconicalflask.Add2to3dropsofa
phenolphthaleinindicatortoit.RunN/50HClfromaburette,tillthepinkcolour
isdisappeared.Thentothesamesolution,add2to3dropsofmethylorange,
continuethetitration,tillthecolorchangesfromyellowtoorangepink.
N/50 HCl
Sample water
Burette
Conical Flask
ALKALINITY
MATRUSRI
ENGINEERING COLLEGE
Experimental Procedure
Pipetteout100mlwatersampleinacleanconicalflask.Add2to3dropsofa
phenolphthaleinindicatortoit.RunN/50HClfromaburette,tillthepinkcolour
isdisappeared.Thentothesamesolution,add2to3dropsofmethylorange,
continuethetitration,tillthecolorchangesfromyellowtoorangepink.
N/50 HCl
Sample water
Burette
Conical Flask
87
ALKALINITY
MATRUSRI
ENGINEERING COLLEGE
0 ml
P
M
WhenP=0,bothOH
-
&CO
3
2-
ionsareabsent,andalkalinityinthatcasedueto
HCO
3
-
only.
WhenP=½M,onlyCO
3
2-
ionispresent,sincehalfofcarbonateneutralization
reactioni.e.[CO
3
2-
]+[H
+
]→[HCO
3
-
]takesplacewithphenolphthaleinindicator;
whilecompletecarbonateneutralizationreactioni.e.[HCO
3
-
]+[H
+
]→H
2
O+CO
2
occurswhenmethylorangeindicatorused.Thus,alkalinityduetoCO
3
2-
=2P.
WhenP=M,onlyOH
-
ispresent,becauseneitherCO
3
2-
norHCO
3
-
ispresent,thus
alkalinityduetoOH
-
=M.
WhenP>½M,inthiscase,besidesCO
3
2-
,OH
-
ionsarealsopresent.Nowhalfof
CO
3
2-
equaltoM-P;soalkalinityduetocompleteCO
3
2-
=2(M-P)
ThereforealkalinityduetoOH
-
=M-2(M-P)=2P–M.
WhenP<½M,;inthiscase,besidesCO
3
2-
,HCO
3
-
ionsarealsopresentnow
alkalinityduetoCO
3
2-
=2P.Therefore,AlkalinityduetoHCO
3
-
=(M-2P).
ALKALINITY
MATRUSRI
ENGINEERING COLLEGE
0 ml
P
M
WhenP=0,bothOH
-
&CO
3
2-
ionsareabsent,andalkalinityinthatcasedueto
HCO
3
-
only.
WhenP=½M,onlyCO
3
2-
ionispresent,sincehalfofcarbonateneutralization
reactioni.e.[CO
3
2-
]+[H
+
]→[HCO
3
-
]takesplacewithphenolphthaleinindicator;
whilecompletecarbonateneutralizationreactioni.e.[HCO
3
-
]+[H
+
]→H
2
O+CO
2
occurswhenmethylorangeindicatorused.Thus,alkalinityduetoCO
3
2-
=2P.
WhenP=M,onlyOH
-
ispresent,becauseneitherCO
3
2-
norHCO
3
-
ispresent,thus
alkalinityduetoOH
-
=M.
WhenP>½M,inthiscase,besidesCO
3
2-
,OH
-
ionsarealsopresent.Nowhalfof
CO
3
2-
equaltoM-P;soalkalinityduetocompleteCO
3
2-
=2(M-P)
ThereforealkalinityduetoOH
-
=M-2(M-P)=2P–M.
WhenP<½M,;inthiscase,besidesCO
3
2-
,HCO
3
-
ionsarealsopresentnow
alkalinityduetoCO
3
2-
=2P.Therefore,AlkalinityduetoHCO
3
-
=(M-2P).
88
ALKALINITY
MATRUSRI
ENGINEERING COLLEGE
Alkalinity OH
-
ppm CO
3
2-
ppm HCO
3
-
ppm
P=0 0 0 M
P=½M 0 2P 0
P=M M 0 0
P > ½M 2P-M 2(M-P) 0
P < ½M 0 2P M-2P
ALKALINITY
MATRUSRI
ENGINEERING COLLEGE
Alkalinity OH
-
ppm CO
3
2-
ppm HCO
3
-
ppm
P=0 0 0 M
P=½M 0 2P 0
P=M M 0 0
P > ½M 2P-M 2(M-P) 0
P < ½M 0 2P M-2P
89
QUIZ
MATRUSRI
ENGINEERING COLLEGE
1.Which of the following situation never arises with respect to the constituents causing
alkalinity in water ?
a) CO
3
2-
and HCO
3
–
together b) HCO
3
–
and OH
–
together
c) OH
–
only d) OH
–
and CO
3
2-
together
2.Which of the following indicator is pink in basic medium?
a) Methyl orange b) Phenolphthalein
c) Starch d) Litmus paper
3.The alkalinity due to hydroxide ion when P > 1/2M will be ____________
a) M-2P b) 2(M-P)
c) 2P-M d) Nil
4.The alkalinity due to carbonate ion is 2P when?
a) P = M b) P > 1/2M
c) P = 1/2Md) P < 1/2M
5.The alkalinity due to bicarbonate ion when P < M/2 will be ____________
a) M-2P b) 2(M-P)
c) d) 2P-M d) Nil
QUIZ
MATRUSRI
ENGINEERING COLLEGE
1.Which of the following situation never arises with respect to the constituents causing
alkalinity in water ?
a) CO
3
2-
and HCO
3
–
together b) HCO
3
–
and OH
–
together
c) OH
–
only d) OH
–
and CO
3
2-
together
2.Which of the following indicator is pink in basic medium?
a) Methyl orange b) Phenolphthalein
c) Starch d) Litmus paper
3.The alkalinity due to hydroxide ion when P > 1/2M will be ____________
a) M-2P b) 2(M-P)
c) 2P-M d) Nil
4.The alkalinity due to carbonate ion is 2P when?
a) P = M b) P > 1/2M
c) P = 1/2Md) P < 1/2M
5.The alkalinity due to bicarbonate ion when P < M/2 will be ____________
a) M-2P b) 2(M-P)
c) d) 2P-M d) Nil
MODULE-12: ION EXCHANGE METHOD
Removal of all ions present in water is called demineralization.
IonExchangeResin:
•Ionexchangeresinsareinsoluble,crosslinked,longchainorganic
polymerswithamicro-porousstructure.
•Theionexchangepropertyofthesepolymersisduetomainlythe
functionalgroupsattachedtothem.
•Thesefunctionalgroupsmaybeacidicorbasic.
•Basedonfunctionalgroupstheresinsmaybeclassifiedas:
a)Cationexchangeresinsb)Anionexchangeresins.
90
MATRUSRI
ENGINEERING COLLEGE
Removal of all ions present in water is called demineralization.
IonExchangeResin:
•Ionexchangeresinsareinsoluble,crosslinked,longchainorganic
polymerswithamicro-porousstructure.
•Theionexchangepropertyofthesepolymersisduetomainlythe
functionalgroupsattachedtothem.
•Thesefunctionalgroupsmaybeacidicorbasic.
•Basedonfunctionalgroupstheresinsmaybeclassifiedas:
a)Cationexchangeresinsb)Anionexchangeresins.
90
MATRUSRI
ENGINEERING COLLEGE
Cation Exchange Resins (RH
+
)
Styrene-divinylbenzenecopolymers,whichonsulphonationor
carboxylation,-SO
3Hor–COOHgroupsareintroducedtopolymers.
TheybecomecapabletoexchangetheirH
+
ionswiththecationin
water.
91
MATRUSRI
ENGINEERING COLLEGE
+
)
Styrene-divinylbenzenecopolymers,whichonsulphonationor
carboxylation,-SO
3Hor–COOHgroupsareintroducedtopolymers.
TheybecomecapabletoexchangetheirH
+
ionswiththecationin
water.
91
MATRUSRI
ENGINEERING COLLEGE
Anion Exchange Resins (R’OH
-
)
Styrene-divinylbenzeneoraminoformaldehydecopolymers,which
containaminoorquaternaryammoniumorquaternaryphosphonium
groupsasanintegralpartoftheresinmatrix.
These,aftertreatmentwithdil.NaOHsolution,becomecapableto
exchangetheirOH
-
ionwiththeanionsinwater.
92
MATRUSRI
ENGINEERING COLLEGE
-
)
Styrene-divinylbenzeneoraminoformaldehydecopolymers,which
containaminoorquaternaryammoniumorquaternaryphosphonium
groupsasanintegralpartoftheresinmatrix.
These,aftertreatmentwithdil.NaOHsolution,becomecapableto
exchangetheirOH
-
ionwiththeanionsinwater.
92
MATRUSRI
ENGINEERING COLLEGE
93
MATRUSRI
ENGINEERING COLLEGE
MATRUSRI
ENGINEERING COLLEGE
In CationExchanger:
•2 RH
+
+ Ca
2+
→R
2Ca
2+
+ 2 H
+
•2 RH
+
+ Mg
2+
→R
2Mg
2+
+ 2 H
+
In Anion Exchanger:
•R’OH
-
+ Cl
-
→R’Cl
-
+ OH
-
•2R’OH
-
+ SO
4
2-
→R’
2SO
4
2-
+ 2 OH
-
•2R’OH
-
+ CO
3
2-
→R’
2CO
3
2-
+ 2 OH
-
•The H
+
and OH
-
ions released from both the column get
combined to produce water molecule.
H
+
+ OH
-
→H
2O
94
MATRUSRI
ENGINEERING COLLEGE
•2 RH
+
+ Ca
2+
→R
2Ca
2+
+ 2 H
+
•2 RH
+
+ Mg
2+
→R
2Mg
2+
+ 2 H
+
In Anion Exchanger:
•R’OH
-
+ Cl
-
→R’Cl
-
+ OH
-
•2R’OH
-
+ SO
4
2-
→R’
2SO
4
2-
+ 2 OH
-
•2R’OH
-
+ CO
3
2-
→R’
2CO
3
2-
+ 2 OH
-
•The H
+
and OH
-
ions released from both the column get
combined to produce water molecule.
H
+
+ OH
-
→H
2O
94
MATRUSRI
ENGINEERING COLLEGE
Regeneration of Ion Exchangers
The exhausted cationexchange resin is regenerated by passing a
solution of dil.HClor dil.H
2SO
4.
R
2Ca
2+
+ 2 H
+
→2 RH
+
+ Ca
2+
(washings)
R
2Mg
2+
+ 2 H
+
→2 RH
+
+ Mg
2+
(washings)
The exhausted anion exchange resin is regenerated by passing a
solution of dil.NaOH.
R’
2SO
4
2-
+ 2 OH
-
→2R’OH
-
+ SO
4
2-
(washings)
R’
2CO
3
2-
+ 2 OH
-
→2R’OH
-
+ CO
3
2-
(washings)
R’Cl
-
+ OH
-
→R’OH
-
-+ Cl
-
(washings)
The columns are washed with deionizedwater and washings which
contain Ca
2+
, Mg
2+
, SO
4
2-
, Cl
-
ions are passed to sink or drain.
95
MATRUSRI
ENGINEERING COLLEGE
The exhausted cationexchange resin is regenerated by passing a
solution of dil.HClor dil.H
2SO
4.
R
2Ca
2+
+ 2 H
+
→2 RH
+
+ Ca
2+
(washings)
R
2Mg
2+
+ 2 H
+
→2 RH
+
+ Mg
2+
(washings)
The exhausted anion exchange resin is regenerated by passing a
solution of dil.NaOH.
R’
2SO
4
2-
+ 2 OH
-
→2R’OH
-
+ SO
4
2-
(washings)
R’
2CO
3
2-
+ 2 OH
-
→2R’OH
-
+ CO
3
2-
(washings)
R’Cl
-
+ OH
-
→R’OH
-
-+ Cl
-
(washings)
The columns are washed with deionizedwater and washings which
contain Ca
2+
, Mg
2+
, SO
4
2-
, Cl
-
ions are passed to sink or drain.
95
MATRUSRI
ENGINEERING COLLEGE
Advantages of Ion Exchange Method
•The process can be used to soften highly acidic or basic waters.
•It produces water of very low hardness (2ppm), so it is very good
for treating water for use in high pressure boilers.
96
MATRUSRI
ENGINEERING COLLEGE
•The process can be used to soften highly acidic or basic waters.
•It produces water of very low hardness (2ppm), so it is very good
for treating water for use in high pressure boilers.
96
MATRUSRI
ENGINEERING COLLEGE
Disadvantages of Ion Exchange Method
•The equipment is costly and more expensive chemicals are needed.
•If water contains turbidity, then the output of the process is reduced.
•The turbidity must be below 10ppm. If it is more it has to be removed
first by coagulation and filtration.
97Matrusri Engineering College
MATRUSRI
ENGINEERING COLLEGE
•The equipment is costly and more expensive chemicals are needed.
•If water contains turbidity, then the output of the process is reduced.
•The turbidity must be below 10ppm. If it is more it has to be removed
first by coagulation and filtration.
97Matrusri Engineering College
MATRUSRI
ENGINEERING COLLEGE
QUIZ
1. Which method are used for preparing of demineralizedwater?
a) Gas Chromatography b) Batch method ( ion exchange)
c) Mass spectroscopy d) ComplexometricTitration
2. Ion-exchange resin is
a) Linear b) Low molecular weight
c) Organic polymer with porous structured) Soluble polymer
3. Which of the following ion get released from the anion exchange column?
a) CO
3
-2
b) OH
–
c) Cl
–
d) SO
4
-2
4. The residual hardness after the treatment of water is about __________
a) 1 ppm b) Less than 1ppm
c) about 2 ppm d) 3ppm
98
MATRUSRI
ENGINEERING COLLEGE
1. Which method are used for preparing of demineralizedwater?
a) Gas Chromatography b) Batch method ( ion exchange)
c) Mass spectroscopy d) ComplexometricTitration
2. Ion-exchange resin is
a) Linear b) Low molecular weight
c) Organic polymer with porous structured) Soluble polymer
3. Which of the following ion get released from the anion exchange column?
a) CO
3
-2
b) OH
–
c) Cl
–
d) SO
4
-2
4. The residual hardness after the treatment of water is about __________
a) 1 ppm b) Less than 1ppm
c) about 2 ppm d) 3ppm
98
MATRUSRI
ENGINEERING COLLEGE
MODULE-13: REVERSE OSMOSIS
Osmosis:Whentwosolutionsofunequalconcentrationsareseparated
byasemipermeablemembraneflowofsolventtakesplacefrom
dilutetoconcentratedsides.
99
MATRUSRI
ENGINEERING COLLEGE
Semipermeablemembrane:does
notpermittheions,atoms,
moleculesetc.
Osmosis:Whentwosolutionsofunequalconcentrationsareseparated
byasemipermeablemembraneflowofsolventtakesplacefrom
dilutetoconcentratedsides.
99
MATRUSRI
ENGINEERING COLLEGE
Semipermeablemembrane:does
notpermittheions,atoms,
moleculesetc.
Reverse Osmosis
Principle:If,however,ahydrostaticpressureinexcessofosmotic
pressureisappliedontheconcentratedside,thesolventflow
reverses,i.e.solventisforcedtomovefromconcentratedsideto
dilutesideacrossthemembrane.
100
MATRUSRI
ENGINEERING COLLEGE
Principle:If,however,ahydrostaticpressureinexcessofosmotic
pressureisappliedontheconcentratedside,thesolventflow
reverses,i.e.solventisforcedtomovefromconcentratedsideto
dilutesideacrossthemembrane.
100
MATRUSRI
ENGINEERING COLLEGE
Thus,inreverseosmosisprocessmethodspurewaterisseparatedfrom
itscontaminants,ratherthanremovingcontaminantsfromthewater.
Thismembranefiltrationissometimesalsocalled“Super-filtration”or
“Hyperfiltration”.
101
MATRUSRI
ENGINEERING COLLEGE
itscontaminants,ratherthanremovingcontaminantsfromthewater.
Thismembranefiltrationissometimesalsocalled“Super-filtration”or
“Hyperfiltration”.
101
MATRUSRI
ENGINEERING COLLEGE
Process:
Inthisprocess,pressureoftheorder15to40kgcm
2-
isappliedtothesea
water/impurewatertoforceitspurewateroutthroughthesemi
permeablemembranes;leavingbehindthedissolvedsolids.
102
MATRUSRI
ENGINEERING COLLEGE
Inthisprocess,pressureoftheorder15to40kgcm
2-
isappliedtothesea
water/impurewatertoforceitspurewateroutthroughthesemi
permeablemembranes;leavingbehindthedissolvedsolids.
102
MATRUSRI
ENGINEERING COLLEGE
Semi-permeable Membrane
Themembraneconsistsofverythinfilmofcelluloseacetate,affixedto
eithersideofaperforatedtube.
Morerecentlysuperiormembranesmadeofpolymethacrylateand
polyamidepolymershavecomeintouse.
103
MATRUSRI
ENGINEERING COLLEGE
Themembraneconsistsofverythinfilmofcelluloseacetate,affixedto
eithersideofaperforatedtube.
Morerecentlysuperiormembranesmadeofpolymethacrylateand
polyamidepolymershavecomeintouse.
103
MATRUSRI
ENGINEERING COLLEGE
Advantages of Reverse Osmosis:
Reverseosmosisprocessisadistinctadvantageofremovingionicas
wellasnonionic,colloidalandhighmolecularweightorganic
matter.
Itremovescolloidalsilica,whichisnotremovedbydemineralization.
Themaintenancecostisalmostentirelyonthereplacementofthe
semipermeablemembrane.
Thelifetimeofmembraneisquitehigh,about2years.
Themembranecanbereplacedwithinafewminutes,thereproviding
uninterruptedwatersupply.
104
MATRUSRI
ENGINEERING COLLEGE
Reverseosmosisprocessisadistinctadvantageofremovingionicas
wellasnonionic,colloidalandhighmolecularweightorganic
matter.
Itremovescolloidalsilica,whichisnotremovedbydemineralization.
Themaintenancecostisalmostentirelyonthereplacementofthe
semipermeablemembrane.
Thelifetimeofmembraneisquitehigh,about2years.
Themembranecanbereplacedwithinafewminutes,thereproviding
uninterruptedwatersupply.
104
MATRUSRI
ENGINEERING COLLEGE
Advantages of Reverse Osmosis
Duetolowcapitalcost,simplicity,lowoperatingcostandhighreliability,
thereverseosmosisisgaininggroundatpresentforconvertingsea
waterintodrinkingwaterandforobtainingwaterforveryhigh
pressureboilers.
105
MATRUSRI
ENGINEERING COLLEGE
Duetolowcapitalcost,simplicity,lowoperatingcostandhighreliability,
thereverseosmosisisgaininggroundatpresentforconvertingsea
waterintodrinkingwaterandforobtainingwaterforveryhigh
pressureboilers.
105
MATRUSRI
ENGINEERING COLLEGE
QUIZ
1. The phenomenon of reverse osmosis involve
a) Osmotic pressure is greater than the hydrostatic pressure
b) Osmotic pressure is equal to the hydrostatic pressure
c) Hydrostatic pressure is greater than the osmotic pressure
d) Diffusion
2. Semi-permeable membrane is selective membrane which permits the passage of
________ particles.
a) Solvent b) Solute
c) Anhydrousd) Saturated
3. Which of the following is used as semi-permeable membrane?
a) Polymethylacrylateb) Cellulose acetate
c) Polyamide polymerd) all the above
4. Select the incorrect statement about reverse osmosis from the following option.
a) It operates at a high temperature
b) Semipermeablemembrane can be easily replaced within a few minutes
c) It is simple and reliable process
d) It is relatively energy efficient
106
MATRUSRI
ENGINEERING COLLEGE
1. The phenomenon of reverse osmosis involve
a) Osmotic pressure is greater than the hydrostatic pressure
b) Osmotic pressure is equal to the hydrostatic pressure
c) Hydrostatic pressure is greater than the osmotic pressure
d) Diffusion
2. Semi-permeable membrane is selective membrane which permits the passage of
________ particles.
a) Solvent b) Solute
c) Anhydrousd) Saturated
3. Which of the following is used as semi-permeable membrane?
a) Polymethylacrylateb) Cellulose acetate
c) Polyamide polymerd) all the above
4. Select the incorrect statement about reverse osmosis from the following option.
a) It operates at a high temperature
b) Semipermeablemembrane can be easily replaced within a few minutes
c) It is simple and reliable process
d) It is relatively energy efficient
106
MATRUSRI
ENGINEERING COLLEGE
MODULE-14:SPECIFICATIONS OF POTABLE WATER
It should be
•Sparkling clear and odorless.
•Pleasant in taste.
•Perfectly cool.
•Turbidity should not exceed 10 ppm.
•It should be free from objectionable minerals such as Pb, As, Cr, Mn
salts.
•It should be free from objectionable gases like H
2S.
•pH should be in range of 7.0 –8.0. Alkalinity should not be high.
•Dissolved solid should be less than 500 ppm.
•It should be soft and free from disease causing micro-organisms.
•Fluoride content should be less 1.5 ppm. And Chloride, Sulphate
contents should be less than 250 ppm.
107
MATRUSRI
ENGINEERING COLLEGE
It should be
•Sparkling clear and odorless.
•Pleasant in taste.
•Perfectly cool.
•Turbidity should not exceed 10 ppm.
•It should be free from objectionable minerals such as Pb, As, Cr, Mn
salts.
•It should be free from objectionable gases like H
2S.
•pH should be in range of 7.0 –8.0. Alkalinity should not be high.
•Dissolved solid should be less than 500 ppm.
•It should be soft and free from disease causing micro-organisms.
•Fluoride content should be less 1.5 ppm. And Chloride, Sulphate
contents should be less than 250 ppm.
107
MATRUSRI
ENGINEERING COLLEGE
STERILIZATION BY CHLORINATION
Chlorinationisthemostcommonlyuseddisinfectantinwatertreatment
throughoutworld.
Itcanbeemployeddirectlyasgasorintheformofconcentratedsolution
inwater.
Itproduceshypochlorousacid,whichisapowerfulgermicide.
Cl
2+H
2O→HOCl+HCl
Bacteria+HOCl→Bacteriaarekilled
108
MATRUSRI
ENGINEERING COLLEGE
Chlorinationisthemostcommonlyuseddisinfectantinwatertreatment
throughoutworld.
Itcanbeemployeddirectlyasgasorintheformofconcentratedsolution
inwater.
Itproduceshypochlorousacid,whichisapowerfulgermicide.
Cl
2+H
2O→HOCl+HCl
Bacteria+HOCl→Bacteriaarekilled
108
MATRUSRI
ENGINEERING COLLEGE
CHLORINTOR (Dosage:0.3 to 0.5ppm)
109
MATRUSRI
ENGINEERING COLLEGE
109
MATRUSRI
ENGINEERING COLLEGE
Factors affecting efficiency of chlorine
Temperatureofwater:Therateofreactionwithenzymesincreaseswith
temperature.Consequently,deathrateofmicro-organismsbychlorine
increaseswithriseintemperature.
Timeofcontact:Deathrateofmicro-organismsbychlorineisproportional
tothenumberofmicro-organismsremainingalive.Initially,thedeath
rateismaximumandwithtime,itgoesondecrease.
pHofwater:atlowerpHvalues(between5–6.5),asmallcontactis
requiredtokillorganisms.
110
MATRUSRI
ENGINEERING COLLEGE
Temperatureofwater:Therateofreactionwithenzymesincreaseswith
temperature.Consequently,deathrateofmicro-organismsbychlorine
increaseswithriseintemperature.
Timeofcontact:Deathrateofmicro-organismsbychlorineisproportional
tothenumberofmicro-organismsremainingalive.Initially,thedeath
rateismaximumandwithtime,itgoesondecrease.
pHofwater:atlowerpHvalues(between5–6.5),asmallcontactis
requiredtokillorganisms.
110
MATRUSRI
ENGINEERING COLLEGE
Advantages of Chlorination
•Itiseffectiveandeconomical.
•Itisstable,requiressmallspaceforstorage,anddoesnot
deteriorateonkeeping.
•Itcanbeusedathighaswellaslowtemperatures.
•Itdoesnotintroduceanyimpurityinwater.
•Itismostidealdisinfectant.
111
MATRUSRI
ENGINEERING COLLEGE
•Itiseffectiveandeconomical.
•Itisstable,requiressmallspaceforstorage,anddoesnot
deteriorateonkeeping.
•Itcanbeusedathighaswellaslowtemperatures.
•Itdoesnotintroduceanyimpurityinwater.
•Itismostidealdisinfectant.
111
MATRUSRI
ENGINEERING COLLEGE
Disadvantages of Chlorination
•Excessofchlorine,producesbadtasteanddisagreeableodor.
•Excesschlorineproducesirritationonmucousmembrane.
•Thequantityoffreechlorineintreatedwatershouldnotexceed0.1to
0.2ppm.
•ItismoreeffectivebelowpH6.5andlesseffectiveathigherpHvales.
112
MATRUSRI
ENGINEERING COLLEGE
•Excessofchlorine,producesbadtasteanddisagreeableodor.
•Excesschlorineproducesirritationonmucousmembrane.
•Thequantityoffreechlorineintreatedwatershouldnotexceed0.1to
0.2ppm.
•ItismoreeffectivebelowpH6.5andlesseffectiveathigherpHvales.
112
MATRUSRI
ENGINEERING COLLEGE
QUIZ
1.The pH for the potable water should be in the range of
a) 5-6 b) 7-8.5
c) 9-10 d) 12-13
2.The total hardness of the potable water should be less than
a) 500 ppm b) 700 ppm
c) 900 ppm d) 1000 ppm
3.What is the chemical formula of bleaching powder?
a) Ca(OCl)
2 b) Ca(OCl)
c) Ca(OCl)
3 d) CaCl
2
4.The commonly used chemicals to treat municipal water
a) Chlorineb) bleaching powder
c) Ozone d) all the above
113
MATRUSRI
ENGINEERING COLLEGE
1.The pH for the potable water should be in the range of
a) 5-6 b) 7-8.5
c) 9-10 d) 12-13
2.The total hardness of the potable water should be less than
a) 500 ppm b) 700 ppm
c) 900 ppm d) 1000 ppm
3.What is the chemical formula of bleaching powder?
a) Ca(OCl)
2 b) Ca(OCl)
c) Ca(OCl)
3 d) CaCl
2
4.The commonly used chemicals to treat municipal water
a) Chlorineb) bleaching powder
c) Ozone d) all the above
113
MATRUSRI
ENGINEERING COLLEGE
MODULE-15 :BREAK-POINT CHLORINATION
Itmeansthatchlorinationofwatertosuchanextentthatlivingorganisms
aswellasotherorganicimpuritiesinwateraredestroyed.
Itinvolvesinadditionofsufficientamountofchlorinetooxidizeorganic
matter,reducingsubstancesandfreeammoniainrawwater,
Leavingbehindmainlyfreechlorinewhichpossessesdisinfectingaction
againstpathogenicbacteria’s.
Itisalsoknownasfree-residualchlorination.
114
MATRUSRI
ENGINEERING COLLEGE
Itmeansthatchlorinationofwatertosuchanextentthatlivingorganisms
aswellasotherorganicimpuritiesinwateraredestroyed.
Itinvolvesinadditionofsufficientamountofchlorinetooxidizeorganic
matter,reducingsubstancesandfreeammoniainrawwater,
Leavingbehindmainlyfreechlorinewhichpossessesdisinfectingaction
againstpathogenicbacteria’s.
Itisalsoknownasfree-residualchlorination.
114
MATRUSRI
ENGINEERING COLLEGE
Break-Point Chlorination
115
MATRUSRI
ENGINEERING COLLEGE
115
MATRUSRI
ENGINEERING COLLEGE
Advantages
•It ensures complete destruction of organic matter which impart color,
bad odor and unpleasant taste to water.
•It completely destroys all the disease causing bacteria.
•It prevents the growth of any weeds in water.
116
MATRUSRI
ENGINEERING COLLEGE
•It ensures complete destruction of organic matter which impart color,
bad odor and unpleasant taste to water.
•It completely destroys all the disease causing bacteria.
•It prevents the growth of any weeds in water.
116
MATRUSRI
ENGINEERING COLLEGE
QUIZ
1.The permissible limit of free residual chlorine is ___________
a) 0.02ppm b) 0.2ppm
c) 1ppm d) 2ppm
2.Chlorine which gets consumed in the oxidation of impurities before disinfection is
a) Free chlorine b) Residual chlorine
c) Chlorine demand d) Residual demand
3.The normal dose of chlorine during break point chlorination is ____________
a) 0.5-1ppm b) 0.1-0.2ppm
c) 3-7ppm d) 1-2ppm
4. The point at which chlorine demand has been totally satisfied, i.ethe chlorine has
reacted with all reducing agents, organics, and ammonia in the water is
a) Residual Point b) Break point chlorination
c) chlorine demand pointd) none of the above
117
MATRUSRI
ENGINEERING COLLEGE
1.The permissible limit of free residual chlorine is ___________
a) 0.02ppm b) 0.2ppm
c) 1ppm d) 2ppm
2.Chlorine which gets consumed in the oxidation of impurities before disinfection is
a) Free chlorine b) Residual chlorine
c) Chlorine demand d) Residual demand
3.The normal dose of chlorine during break point chlorination is ____________
a) 0.5-1ppm b) 0.1-0.2ppm
c) 3-7ppm d) 1-2ppm
4. The point at which chlorine demand has been totally satisfied, i.ethe chlorine has
reacted with all reducing agents, organics, and ammonia in the water is
a) Residual Point b) Break point chlorination
c) chlorine demand pointd) none of the above
117
MATRUSRI
ENGINEERING COLLEGE
MATRUSRI
ENGINEERING COLLEGE
118
ENGINEERING COLLEGE
118
Tags
Categories
ScienceDownload
Download Slideshow Get the original presentation fileQuick Actions
Statistics
- Views 1,111
- Slides 118
- Favorites 2
- Age 1522 days
Related Slideshows
23
Earthquakes_Type of Faults_Science G8.pptx
OctabellFabila1
31 views
15
Quiz #1 Science 10 in the first quarter for jhs
HendrixAntonniAmante
30 views
9
Astronomy history from long ago till doday
ssuserbd9abe
29 views
9
Great history of astronomy from long ago till today
ssuserbd9abe
27 views
20
EARTHQUAKE-DRILL.powerpoint.............
chalobrido8
30 views
9
History of astronomy from old times to the present times
ssuserbd9abe
30 views