Engineering chemistry[As per New CBCS Scheme for I/II semester BE courses of VTU, bengaluru]

ENGINEERING
CHEMISTRY
[As per New CBCS Scheme, for I/II Semester
B.E. courses of VTU, Karnataka]
By,
RASHMI M
Assistant Professor, Dept. of Chemistry
Sri Krishna Institute of Technology,
Bengaluru

ENGG.CHEMISTRY [RM] Page 2
Table of Contents
MODULE-1:.................................................................................................................................7
ELECTROCHEMISTRY ............................................................................................................7
1.1 Electrochemistry:...................................................................................................................7
1.2 Electrochemical series:...........................................................................................................8
1.3 Derivation of Nernst Equation for Electrode potential:............................................................9
1.4 Concentrations cells:............................................................................................................ 10
1.5 Reference Electrodes: .......................................................................................................... 12
1.6 Construction and working of Standard Calomel electrode (SCE):............................................ 12
1.7 Measurement of single electrode potential using calomel electrode: .................................... 13
1.8 Construction and working of Silver- Silver Chloride electrode:............................................... 14
1.9 Ion selective electrode (ISE):................................................................................................. 15
1.10 Construction and working of Glass electrode: ..................................................................... 15
1.10 Determination of pH using glass electrode:......................................................................... 16
1.11 Numerical on concentration cell: ........................................................................................ 17
1.12 Questions: ......................................................................................................................... 19
MODULE-1 :............................................................................................................................ 20
BATTERY TECHNOLOGY..................................................................................................... 20
1.13 Battery: ............................................................................................................................. 20
1.14 Principal Component Of A Battery: ..................................................................................... 20
1.15 Classification of batteries: .................................................................................................. 20
1.16 Operation of a battery during discharging and charging: ..................................................... 20
1.17 characteristics of a battery: ................................................................................................ 21
1.18 Zn-air cell (Primary battery, non rechargeable) ................................................................... 22
1.19 Li-MnO2 cell: (primary battery, non rechargeable) .............................................................. 23
1.20 Lithium-ion batteries.......................................................................................................... 24
1.21 Nickel-metal hydride battery.............................................................................................. 26
1.22 Fuel cells:........................................................................................................................... 26
1.23 Methanol – Oxygen fuel cell ............................................................................................... 27
Questions:................................................................................................................................. 28
MODULE-2 :............................................................................................................................ 29
CORROSION............................................................................................................................ 29
2.1 Definition of corrosion: ........................................................................................................ 29
2.2 Types of corrosion:............................................................................................................... 29
2.3 Electrochemical theory of corrosion: .................................................................................... 29

2.4 Galvanic Series:.................................................................................................................... 31
2.5 Different types of corrosion: ................................................................................................ 32
2.6 Differential metal corrosion: ................................................................................................ 32
2.7 Differential aeration corrosion: ............................................................................................ 32
2.8 Water line corrosion: ........................................................................................................... 33
2.9 Pitting corrosion: ................................................................................................................. 33
2.10 Stress corrosion: ................................................................................................................ 34
2.11 Factors affecting the rate of corrosion: ............................................................................... 34
2.12 Corrosion control ............................................................................................................... 36
2.12 Anodizing (Anodizing of aluminum): ................................................................................... 36
2.13 Phosphating:...................................................................................................................... 37
2.14 Metal coatings: .................................................................................................................. 37
2.15 Anodic metal coating: ........................................................................................................ 37
2.15 Galvanizing of iron : ........................................................................................................... 37
2.16 Cathodic metal coating :..................................................................................................... 38
2.16 Tinning: ............................................................................................................................. 38
2.17 Cathodic protection:- ......................................................................................................... 38
2.18 Sacrificial anode method:................................................................................................... 39
2.19 Impressed current method (impressed voltage method): .................................................... 39
2.20 Questions: ......................................................................................................................... 40
MODULE-2 : .............................................................................................................................. 41
Metal finishing ................................................................................................................ 41
2.21 Definition of metal finishing:.............................................................................................. 41
2.22 Technological importance of metal finishing:...................................................................... 41
2.23 Electroplating:.................................................................................................................... 41
2.24 Polarization: ...................................................................................................................... 41
2.25 Decomposition potential [Ed].............................................................................................. 42
2.26 Over voltage over potential η ........................................................................................ 43
2.27 Principal components of an electroplating process:............................................................. 43
2.28 Effect of plating variables on the property of electrodeposit: .............................................. 44
2.29 Electroplating of chromium ................................................................................................ 46
2.30 Electroplating of Nickel by watt’s method :......................................................................... 47
2.31 Electroless plating:............................................................................................................. 48
2.32 Distinction between electroplating and electroless plating:................................................. 48
2.33 Electroless plating of Copper .............................................................................................. 49
2.34 Through-hole connection is PCB’s:...................................................................................... 49

2.35 Questions: ......................................................................................................................... 50
MODULE-3:............................................................................................................................... 51
Chemical fuels & solar cells.................................................................................. 51
3.0 Definition of a chemical fuel:................................................................................................ 51
3.1 Classification of chemical fuels: ............................................................................................ 51
3.2 Definition of calorific value of a fuel [Gross calorific value]:.................................................. 51
3.3 Definition of net calorific value:............................................................................................ 52
3.4 Determination of calorific value of a solid fuel using Bomb Calorimeter: ............................... 52
3.5 Numerical on GCV & NCV: .................................................................................................... 53
3.6 Cracking............................................................................................................................... 57
3.7 Fluidized bed catalytic cracking: ........................................................................................... 57
3.8 Reformation of petrol .......................................................................................................... 58
3.9 Synthesis of petrol by Fischer-Tropsch process:.................................................................... 59
3.10 Knocking in petrol engine:.................................................................................................. 60
3.11 Mechanism of knocking in chemical terms:......................................................................... 60
3.12 Antiknocking agent for Petrol engine:................................................................................. 61
3.13 Definition of octane number: ............................................................................................. 61
3.14 Knocking in diesel engine: ................................................................................................. 62
3.15 Antiknocking agent for diesel engine: ................................................................................. 62
3.16 Cetane number: ................................................................................................................. 62
3.17 Power Alcohol.................................................................................................................... 62
3.18 Biodiesel:........................................................................................................................... 63
3.19 Solar Energy....................................................................................................................... 64
3.20 Photovoltaic Cells:.............................................................................................................. 64
3.21 Construction & Working of Photovoltaic Cell: ..................................................................... 64
3.22 Photovoltaic Module , Panel & Array.................................................................................. 65
3.33 Production of solar grade silicon:........................................................................................ 66
3.34 The Union Carbide process:................................................................................................ 66
3.35 Purification of Silicon by Zone refining Process................................................................. 67
3.36 Doping of Silicon: ............................................................................................................... 67
3.37 Diffusion Technique: .......................................................................................................... 68
3.38 Doping of Silicon by Diffusion Technique: ........................................................................... 68
3.39 Questions : ........................................................................................................................ 68
MODULE-4:............................................................................................................................... 69
High polymers................................................................................................................... 69
4.0 POLYMER:............................................................................................................................ 69

4.1 Polymerization:.................................................................................................................... 69
4.2 Degree of polymerization..................................................................................................... 69
4.3 Classification of polymers:.................................................................................................... 69
4.4 Explain free radical mechanism of addition polymerization by taking Vinyl Chloride as an
example.................................................................................................................................... 70
4.5 Molecular mass of polymers:................................................................................................ 72
4.6 Number – average molecular mass [
n
M ] :........................................................................... 72
4.7 Mass – average molecular mass
w
M : ................................................................................. 72
4.8 Poly Dispersity Index [PDI]: .................................................................................................. 72
4.9 Numerical on Number average & weight average Molecular Mass: ....................................... 73
4.10 Glass transition temperature (Tg): ...................................................................................... 75
4.11 Factors influencing Tg value: .............................................................................................. 75
4.12 Structure-property relationship:......................................................................................... 77
4.13 Synthesis, properties and applications of few polymers: ..................................................... 77
4.14 Polymethylmethacrylate(PMMA-Plexi glass):...................................................................... 77
4.15 Polyurethanes:................................................................................................................... 78
4.16 Polycarbonates: ................................................................................................................. 78
4.17 Elastomers:........................................................................................................................ 79
4.18 Silicone rubber:.................................................................................................................. 79
4.19 Adhesives: ......................................................................................................................... 80
4.20 Preparation, properties and applications of epoxy resin:..................................................... 80
4.21 Polymer composites:.......................................................................................................... 81
4.22 Kevlar fiber:....................................................................................................................... 81
4.23 Conducting polymer:.......................................................................................................... 82
4.24 Mechanism of conduction in polyaniline:............................................................................ 83
4.25 Questions : ........................................................................................................................ 84
MODULE-5:............................................................................................................................... 85
Water technology & nano materials.................................................................. 85
5.1 Source of water: .................................................................................................................. 85
5.2 Nature of impurities in water: .............................................................................................. 85
5.3 Sources of Water: ................................................................................................................ 85
5.4 Boiler feed water & Boiler troubles ...................................................................................... 85
5.5 Sludge and scale: ................................................................................................................. 86
5.6 Differences between sludge and scale: ................................................................................. 86
5.7 Priming and Foaming: .......................................................................................................... 86

5.8 Boiler Corrosion:.................................................................................................................. 87
5.9 Determination of dissolved oxygen (DO) & BOD: [ Winkler’s Method]................................... 87
5.10 Chemical oxygen demand................................................................................................... 89
5.11 Numerical on COD:............................................................................................................. 89
5.12 Sewage treatment:............................................................................................................. 91
5.13 Primary treatment: ............................................................................................................ 91
5.14 Secondary treatment [Activated Sludge Process]: ............................................................... 91
5.15 Tertiary treatment: ............................................................................................................ 92
5.16 Softening of water ............................................................................................................. 93
5.17 Softening of water by ion exchange method [demineralization]: ......................................... 93
5.18 Desalination of water:........................................................................................................ 94
5.19 Reverse osmosis:................................................................................................................ 94
5.20 Electrodialysis :.................................................................................................................. 96
5.21 Questions : ........................................................................................................................ 97
MODULE-5:............................................................................................................................... 98
nano materials ............................................................................................................... 98
5.22 NANO MATERIALS.............................................................................................................. 98
5.23 Nano science...................................................................................................................... 98
5.24 Nanotechnology................................................................................................................. 98
5.25 Size – dependent properties of nano materials: .................................................................. 99
5.26 Surface area:...................................................................................................................... 99
5.27 Electrical properties: ........................................................................................................ 100
5.28 Optical properties: ........................................................................................................... 100
5.29 Synthesis Of Nanoparticles:.............................................................................................. 100
5.30 Bottom Up Approach ....................................................................................................... 101
5.31 Sol – Gel Process: ............................................................................................................. 101
5.32 Precipitation method: ...................................................................................................... 102
5.33 Inert gas condensation..................................................................................................... 103
5.34 Chemical vapour deposition ............................................................................................. 104
5.35 Nano scale materials:....................................................................................................... 104
5.36 Nano wires and nano rods:............................................................................................... 105
5.37 Carbon nanotubes :.......................................................................................................... 105
5.38 Fullerenes:....................................................................................................................... 107
5.39 Nano composites: ............................................................................................................ 109
5.40 Dendrimers:..................................................................................................................... 110
5.41 Questions: ....................................................................................................................... 112

MODULE-1:
ELECTROCHEMISTRY
1.1 Electrochemistry: It is a branch of chemistry which deals with the study of transformation
of chemical energy into electrical energy and vice versa”
Electrochemical cell and Classification with examples:
An electrochemical cell is a device, which is used to convert chemical energy into electrical energy and vice
versa.
These electrochemical cells are classified into two types as follows.
1) Galvanic or Voltaic cells: These are the electrochemical cells, which convert chemical energy into electrical
energy.
Ex. Daniel cell, Dry cell, etc
2) Electrolytic cells-are devices which convert electrical energy into chemical energy.
Example: Electrolysis of molten NaCl, Recharge process of lead acid battery
Galvanic or Voltaic cells:
Galvanic or Voltaic cells are again classified into three types as follows
a) Primary cells: These are the cells which serve as a source of energy only as long as the active chemical
species are present in the cell. The cell reactions are irreversible. These are designed for only single discharge
and cannot be charged again.
Ex: Dry Cell, Zn – Hgo cell, Zn-Ag2o cell etc.
b) Secondary cells: These cells are chargeable and can be used again and again. The cell reactions are
reversible and are often called as reversible cells. During discharging the cells acts like voltaic cell converting
chemical energy into electrical energy. During charging the cell acts like electrolytic cell by converting electric
energy into chemical energy, hence these batteries are called as storage battery.
Ex: Lead acid Battery, Ni-cd cells. Lithium ion cells etc.
c) Concentration of cells:
These are the electrochemical cells consisting of same metalelectrodes dipped in same metal ionic solution in
both the half cells butare different in the concentration of the metal ions.
Ex: Cu/Cu2+
(M1) || Cu2+
(M2)/Cu
Ex: Copper concentration cell, Zinc concentration cell
Oxidation: A species loses one or more electrons resulting in the increase in its oxidation number.
Reduction: A species gain one or more electrons resulting in a decreasing in its oxidation number.

Oxidation should accompanied by reduction, because if one losses electrons another must ready to accept
electrons. This reaction is called redox reaction.
Single electrode Potential:
It is defined as the potential developed at the interphase between the metal and the solution, when a
metal is dipped in a solution containing its own ions. It is represented as E
Standard reduction potential (Eo
) :
It is defined as potential developed at the interface between the metal and the solution, when a metal is dipped
in a solution containing its own ions of unit concentration at 298K. [If the electrodes involve gases then it is one
atmospheric pressure] It is denoted as E0
.
Electromotive force (EMF):
It is defined as the potential difference between the two electrodes of a galvanic cell which causes the flow of
current from an electrode with higher reduction potential to the electrode with lower reduction potential.
It is denoted as E cell.
E cell = E right –E left.
E cell = E cathode – E anode.
1.2 Electrochemical series:
The arrangement of elements in the order of their standard reduction potential is refered as emf or
electrochemical series. Such a arrangement of few elements given in the table.
Mn+
/M Eo
(volts) Mn+
/M Eo
(volts)
Li+
/Li -3.05 H+
/H2 0.00
K+
/K -2.93 Sn4+
/ Sn2+
+0.15
Mg+
/Mg -2.37 Cu2+
/Cu +0.16
Al3+
/Al -1.66 Cu+
/Cu +0.52
Zn2+
/Zn -0.76 I2/I-
+0.54
Cr3+
/Cr -0.74 Fe3+
/Fe2+
+0.77
Fe2+
/Fe -0.44 Hg2+
/Hg+
+0.79
Cr3+
/Cr2+
-0.41 Ag+
/Ag +0.80
Cd2+
/Cd -0.40 Hg2+
/Hg +0.85
Ni2+
/Ni -0.25 Pt2+
/Pt +1.20
Sn2+
/Sn -0.14 Cr7+
/Cr3+
+1.31
Pb2+
/Pb -0.13 Cl2/2Cl-
+1.36
Fe3+
/Fe2+
-0.041 Au3+
/Au +1.50
1) A negative value indicates oxidation tendency and a positive value indicates reduction tendency with respect
to hydrogen.
2) The metal with lower electrode potential is more reactive and as the electrode potential increases, the
reactivity decreases, and metals with higher electrode potentials are nobler.
3) Metals with lower electrode potentials have the tendency to replace metals with higher electrode potential
from their solutions for example, Zn displaces Cu, and Cu displaces Ag
4) Metals with negative electrode potentials can liberate hydrogen from acidic solutions

1.3 Derivation of Nernst Equation for Electrode potential:
In 1889 Nernst derived a quantitative relationship between the electrode potential and the concentrations of
metal ions are involved. The maximum work available from a reversible chemical process is equal to the
maximum amount of electrical energy that can be obtained; it shows decrease in free energy.
Wmax = – ∆G------------------------------------[1]
And
Wmax = difference in potential between two electrode x total quantity of charge flowing through the cell
Total quantity of charge flowing through the cell = (No. of moles of electrons) x (Faradays constant)
So Wmax = nFEcell -----------------------------[2]
Where,
E = Electrode potential
E0
= standard electrode potential
n = no. of electrons
[Mn+
] = Concentration of metal ions
R = Universal gas constant = 8.314J K-1
mol-1
]5[
c
Kln0GG
,isotherm'reactionhoffvant'abyrelatedare0GandG,
c
K
]4[
]n[M
[M]
c
K
aswrittenbecan
c
Kconstantequlibrium,reactionabovefor the
M-nenM
reaction,electrodereversibleaconsider
0nFE-0Gion,std.conditunder
[3]-----nFE-G
[2]&[1]eqnequate








RT
]6[]nlog[M
303.20EE
1[M]condition,standardunder
]n[M
[M]
lnRT0EE
nF-bysidesboth thedivide
]n[M
[M]
ln0-nFEnFE-
equation,abovetheto0GandG,
c
Kofvaluesthesubstitute







nF
RT
nF
RT
RT

T = Temperature (In Kelvin) = 298K
 
 reactant
product
cKwherelog
2
0591.00 
c
KE
cell
E
 
 anodeatSpecies
cathodeatSpecies
log
2
0591.00  E
cell
E
1.4 Concentrations cells:
“A concentration cell is an electrochemical cell in which electrode materials and electrolytes of two half
cells are composed of same material but the concentration of two solutions are different”
Ex- Cu/Cu2+
(M1)|| Cu2+
(M2)/Cu
A concentration cell consists of two same metal electrode dipped into their own ionic solutions of two different
concentration.
Thus in a concentration cell, the electrode with lower electrolyte concentration acts as anode and the one
with higher electrolyte concentration acts as cathode. The concentration of ions at anode increases and at
cathode decreases, when the cell is in operation.
Consider two copper rods are dipped into their own ionic solutions of M1 and M2 and it is represented as
Cu/Cu2+
(M1) Cu2+
(M2)/Cu
By electrochemical conventions, if M2 > M1 then, we have the following reactions.
At anode



 eMCu
s
Cu 2)1(
2
)(
At cathode
]7[]n[Mlog
0591.00 
n
E
cell
E

)(
2)2(
2
s
CueMCu 



The emf of the concentration cell will be



  1log
2
0591.002log
2
0591.00
MEME
cell
E
1
2
log
2
0591.0
M
M
cell
E 
The emf of the cell is + ve only if M2 > M1
The following characteristics of concentration cell can be noted:
1. When M2 = M1, the concentration cell does not generate electrical energy.
2. When M2 > M1, the Ecell is + ve.
3. When M2<M1, Ecell is – ve.
4. Higher the ratio of M2/M1, greater is the cell potential.
Types of electrodes:
1. Metal-Metal ion electrode: An electrode of this type consists of a metal dipped in a solution containing its
ions. Ex- Zn/Zn2+
, Cu/Cu2+
etc
2. Metal-Metal salt ion electrode: These electrodes consist of a metal is in contact with a sparingly soluble salt
of the same metal dipped in a solution containing anion of the salt.
Example-Calomel (Hg|Hg2Cl2|Cl-
, Silver- Silver salt electrode (Ag| AgCl |Cl-
)
3. Gas electrode: Gas electrode consists of a gas bubbling about an inert metal wire, immersed in solution
containing ions to which the gas is reversible. The metal provides electrical contact and facilitates the
establishment of equilibrium between the gas and its ions.
Example-Hydrogen electrode (Pt|H2|H+)
, Chlorine electrode (Pt|Cl2|Cl-
)
4. Oxidation-Reduction electrode: An oxidation-reduction electrode is a one in which the electrode potential
arises from the presence of oxidized and reduced forms of the same substance in solution. The potential arises
from the tendency of one form changes into the other more stable form. The potential developed is picked up by
an inert electrode like platinum.
Example-Pt|Fe2+
, Fe3+
Pt|Ce3+
, Ce4+
5. Ion selective electrode: In ion selective electrode, a membrane is in contact with a solution, with which it can
exchange ions.
Example-Glass electrode.

1.5 Reference Electrodes:
“Reference electrode are the electrode with reference to those, the electrode potential of any electrode
can be measured.”
It can acts both as an anode or cathode depending upon the nature of other electrode.
The Reference Electrodes can be classified in to two types
i) Primary reference electrodes Ex: Standard hydrogen electrode
ii) Secondary reference electrodes Ex: Calomel and Ag/Agcl electrodes
SHE has two main Limitations:
i) The construction of SHE is difficult. It is very difficult to maintain the concentration of H+
as 1M and
pressure H2 gas at 1atm
ii) Platinum electrode is poisoned by the impurities of the gas
1.6 Construction and working of Standard Calomel electrode (SCE):
1. Calomel electrode is a metal-metal salt Ion electrode.
2. It consists of mercury, mercurous Chloride and a solution of KCl. Mercury is placed at the bottom of a
glass tube.
3. A paste of mercury and mercurous chloride Is placed above the mercury. The space above the paste is filled
with a KCl solution of known concentration.
4. A platinum wire is kept immersed into the mercury to obtain electrical contact.
5. Calomel electrode can be represented as,
Hg | Hg2Cl2 | sat KCl
The calomel electrode can acts as anode or cathode depending on the nature of the other electrode of the cell.
The net cell reversible electrode reaction is,
Electrode potential,  20
log.
303.2 
 Cl
nF
RT
EE
 ,log.
303.20 
 Cl
F
RT
EE Where
n=2
Therefore electrode potential of calomel electrode is depending upon the concentration of KCl.
 The electrode is reversible with chloride ions.
 The potential of the calomel electrode depends on the concentration of the KCl.
 
 ClEE log0591.00
at 298K
Saturated KCl
Mercury
Calomel paste
Pt wire
Porous disc
Hg2Cl2(s) + 2e-
2Hg(l) + 2Cl-

For saturated KCl, the potential is 0.241V; For 1M KCl , 0.280V; For 0.1M KCl, 0.334V.
1.7 Measurement of single electrode potential using calomel
electrode:
Electrode potential of a given electrode can be measured by using calomel electrode as a reference electrode.
Example-1: To measure the electrode potential of zinc: To measure the potential of the Zn- electrode, the
Zn- electrode is coupled with the SCE through a salt bridge. The anode and the cathode of the cell can be
identified by connecting the electrodes to the appropriate terminals of the voltmeter. Proper measurements can
be made only when the Zn-electrode is connected to the –ve terminal and the calomel electrode to the +ve
terminal of the voltmeter indicating that Zinc electrode is anode & the calomel electrode is a cathode.
HgClHgsatdKClSOZnZn 224 )(
At anode: Zn Zn2+
+ 2e
At cathode: Hg2Cl2 + 2e-
2Hg + 2C
Overall reaction: Zn + Hg2Cl2 Zn2+
+2Hg + 2Cl-
Ecell = Ecathode- Eanode
=ESCE –EZn
2+
/Zn
=0.2422V – Eo
Zn
2+
/Zn
EZn
2+
/Zn=0.2422-Ecell
EZn
2+
/Zn=0.2422-1.001
EZn
2+
/Zn= - 0.76V
Example-2: To measure the electrode potential of copper: Similarly to determine the copper electrode
potential of the cell, the cell is constructed as follows. Calomel electrode being the anode is connected to –ve
terminal of the voltmeter and copper electrode being the cathode is connected to the +ve terminal of the
voltmeter.
Hg/Hg2Cl2/KCl(sat)//Cu2+
/Cu
At anode: 2Hg + 2Cl-
Hg2Cl2 +2 e-
At cathode: Cu2+
+ 2e Cu
Overall reaction: 2Hg + 2Cl-
+ Cu2+
Hg2Cl2 + Cu
Ecell= Ecathode –Eanode
= Ecu
2+
/cu - ESCE
Ecu
2+
/cu = Ecell + 0.2422
Ecu
2+
/cu = 0.1 + 0.2422
Ecu
2+
/cu = +0.34V
Voltmeter
Calomel
Electrode
copper
Electrode
CuSO4
solution
Voltmeter
zinc
Electrode
Pt wire
ZnSO4
solutiom
Calomel
electrode

Advantages of calomel electrode:-
1. It is easily setup (simple to construct).
2. The cell potential is reproducible and stable over a long period.
3. It is used as a secondary reference electrode in the measurement of single electrode
potential.
4. It is the most commonly used reference electrode in all potentiometric determinations
and to measure pH of the given solution
Applications:
1. It is used as secondary reference electrode in the measurement of single electrode.
2. It is used as reference electrode in all potentiometer determinations and to measure pH of the given
solution.
1.8 Construction and working of Silver- Silver Chloride
electrode:
1. Silver-Silver chloride is also a metal-metal salt ion electrode.
2. Silver and its sparingly soluble salt silver chlorides are in contact with a solution of chloride solution
ions. Generally a silver wire is coated with AgCl and dipped in a solution of KCl .
3. Cell representation is as follows
Ag |AgCl | sat KCl
Net half cell reaction is
AgCl + e-
Ag + Cl-
Electrodepotential  ,log.
303.20 
 Cl
nF
RT
EE Where n=1
 
 Cl
F
RT
EE log
303.20
 Therefore electrode potential of calomel electrode is depending upon
the concentration of KCl.
 The electrode is reversible with chloride ions.
 The potential of the calomel electrode depends on the concentration of the KCl.
For 1N solution, the electrode potential is 0.223V and for saturated solution is 0.199V at 298K
Applications:
1. Used as secondary reference electrode in ion selective elctrode.
2. In determining the distribution of potential on the ship hull and pipe lines.
 
 ClEE log0591.00
at 298K

1.9 Ion selective electrode (ISE):
“Ion selective electrode is one which selectively responds to a specific ion in a mixture and the potential
developed at the electrode is a function of the concentration of that ion in the solution”
1.10 Construction and working of Glass electrode:
A glass electrode is an ion selective electrode where potential depends upon the pH of the medium.
1. The glass electrode consists of a glass bulb made up of special type of glass (sodium silicate type of
glass) with high electrical conductance.
2. The glass bulb is filled with a solution of constant pH (0.1MHCl) and insert with a Ag-AgCl electrode,
which is the Internal reference electrode and also serves for the external electrical contact.
3. The electrode dipped in a solution containing H+
ions as shown in the figure.
4. The electrode representation is,
Glass | 0.1M HCl | Ag/AgCl.
INTERNAL SOLUTION EXTERNAL SOLUTION
C1= CONSTANT C2= [H+
]
E1 E2
Eb
The glass electrode works on the principle that when a thin glass membrane is in contact with a solution , A
boundary potential Eb is developed at layers of the glass membrane. This potential arises due to difference in the
concentration of H+
ion inside and outside the membrane.
Boundary potential, Eb = E2 – E1-------------------------(1)
1
Clog.
0591.00
1 n
EE 
2
log
0591.00
2
C
n
EE 
Where, C1 and C2 are concentration of H+
ions inner and outer membrane.
Substitute the values of E1 & E2 into eqn (1), we get





1
log
0591.00
2
log.
0591.00 C
n
EC
n
EEb
H+
Ion Solution
Ag/AgCl electrode
0.1 M HCl
GLASS ELECTRODE
GLASS
MEMBRANE

1
log
0591.0
2
log
0591.0
C
n
C
n
Eb  (n = 1)
1
log0591.0
2
log0591.0 CCEb 
(n=1, Since the concentration of the inner solution is constant, C1 is constant & (C2) = (H+
))



  HConstEb log0591.0
Where Const = K = -0.0591logC1
The glass electrode potential is sum of the
i) Boundary potential Eb,
ii) Ag-AgCl electrode potential EAg/AgCl and
iii) Asymmetry potential Easy.
asy
E
AgClAg
E
b
E
G
E 
/
Theoritically, Eb = 0 for C1 = C2. However, a small additional potential is exists called Easy
potential.
asy
E
AgClAg
EpHK
G
E 
/
0591.0
asy
E
AgClAg
EKGEwhere 
/
0
1.10 Determination of pH using glass electrode:
Procedure: glass electrode is immersed in the solution; the pH is to be determined. It is combined with a
reference electrode such as a calomel electrode through a salt bridge. The cell assembly is represented as,
pHKEb 0591.0
0591.00 pHGE
G
E 
pH Meter
Calomel
Electrode
Glass
Electrode
Solution of
Unknown pH

Hg| Hg2Cl2|Cl-
||Solution of unknown pH|glass|0.1M HCl|Ag|AgCl
The emf of the above cell, Ecell is measured using an electronic voltmeter with a pH meter.
The emf of the cell is given by
anode
E
cathode
E
cell
E 
……………… (1)
SCE
E
G
E
cell
E 
……………………… (2)
Since E SCE is knowing emf the cell,
E glass can be evaluated.
pHGE
G
E 0591.0
0
 …………………. (3)
SCE
EpHGEEcell  0591.0
0
…………..(4)
Advantages
1. This electrode can be used to determine PH
in the range 0-9, with special type of glass even up to 12 can be
calculated.
2. It can be used even in the case of strong oxidizing agents.
3. The equilibrium is reached quickly.
4. It is simple to operate, hence extensively used in various laboratories.
Limitations
1. The glass membrane though it is very thin, it offers high resistance. Therefore ordinary potentiometers cannot
be used; hence it is necessary to use electronic potentiometers.
2. This electrode cannot be used to determine the PH
above 12
1.11 Numerical on concentration cell:
1. Two Copper electrodes placed in CuSO4 solutions of equal concentration are connected to form o
concentration cell.
a) What is the cell voltage?
b) If one of the solutions is diluted until the concentration of Cu2+
ions is 1/5th
of its original value.
What will be the cell voltage after dilution?
Solution:
a) The cell potential of concentration cell is given as
1
2
log
0591.0
C
C
ncell
E 
When the concentration of the species are gqual (C2 = C1) the cell voltage is zero.
0591.0
0
SCEcellG EEE
pH



b) When one of the solution is diluted to
1
5
ℎ of its original value, C2 =1M & C1=
1
5
1
2
log
0591.0
C
C
ncell
E 
5/1
1
log
2
0591.0

cell
E
5log
2
0591.0

cell
E
699.002955.0 
cell
E
V
cell
E 0206.0
2. Two zinc rods are placed in 0.1M & 1M ZnSO4 solution separately to form a cell. Give the
electrochemical representation of the cell & calculate its emf.
Solution: Cell representation
Zn(S)/ZnSO4 (0.1M) ZnSO4 (1M)/Zn(S)
1
2
log
0591.0
C
C
ncell
E 
1.0
1
log
2
0591.0

cell
E
10log
2
0591.0

cell
E
V
cell
E 0295.0
3. Calculate the emf of the given concentration cell at 298K. Ag(s) /AgNO 3 (0.018M) AgNO3 (1.2M)
/Ag.
Solution :
1
2
log
0591.0
C
C
ncell
E 
018.0
2.1
log
1
0591.0

cell
E
66.66log
1
0591.0

cell
E
V
cell
E 1708.0
4. EMF of the cell Ag/AgNO3 (C1)// AgNO3 (C2=0.2M)/Ag is 0.8V. Calculate C1 of the cell.
Ecell = 0.0591/n logC2/ C1
0.8 = 0.591/1 log (0.2 / C1)
C1 = 5.5 X 10-14
M

5. The spontaneous galvanic cell Tin/Tin –ion (0.024M)//Tin-ion (0.064M)/Tin develops an Emf of
0.0126V at 25O
C. Calculate the valency of Tin.
Ecell = 0.0591/n logC2/ C1
0.0126 = 0.0591/n log (0.064/0.024)
n = 1.998 = 2.
1.12 Questions:
1. What is single electrode potential? Derive the Nernst equation for single electrode potential.
2. What are concentration cells? Deduce the expression for the EMF of a copper concentration cell.
3. Explain the construction & working of CALOMEL electrode.
4. Explain the measurement of electrode potential by using standard calomel electrode
5. Explain the construction & working of Ag/AgCl electrode
6. What is an ion selective electrode?
7. Explain the construction & working of GLASS electrode
8. Explain how glass electrode can be used in the determination of a PH
of a solution.

MODULE-1 :
BATTERY TECHNOLOGY
1.13 Battery:
It is a compact device consisting of two or more galvanic cells connected in series or parallel or
both. It stores chemical energy in the form of active materials and on demand converts it into electrical
energy through redox reactions.
Batteries are used in calculators, digital watches, pace makers, hearing aids, portable computers,
electronically controlled cameras, digital watches, stand by power supplies, emergency lighting and
electroplating, telecommunication, military & space applications.
1.14 Principal Component Of A Battery:
1. An anode where oxidation
2. A cathode where reduction occurs
3. An electrolyte , which is ironically conducting
4. A separator to separate anode and cathode compartments.
1.15 Classification of batteries:
Batteries are classified into three types as follows.
a) Primary
b) Secondary
c) Reserve batteries.
a) Primary Batteries: These are the batteries which serve as a source of energy only as long as the active
chemical species are present in the battery or in the cell. The cell reactions are irreversible. These are
designed for only single discharge and cannot be charged again.
Ex: Dry Cell, Zn – HgO cell, Zn-air cell etc.
b) Secondary Batteries: These batteries are chargeable and can be used again and again. The cell
reactions are reversible and are often called reversible batteries. During discharging the cell acts like
galvanic cell converting chemical energy into electrical energy. During charging the cell acts like
electrolytic cell by converting electric energy into chemical energy, hence these batteries are called as
storage battery.
Ex: Lead acid Battery, Ni-Cd battery etc.
c) Reserve Batteries: The key components of the batteries such as electrolyte etc., is separated from the
rest of the component of the battery. And the battery is stored for a longer time. The electrolyte is filled
before its usage.
Ex: Mg – water activated batteries, Zn-Ag2O Batteries etc.
1.16 Operation of a battery during discharging and charging:
Discharge: During discharge, oxidation takes place at the anode and reduction takes place at the cathode.
The reaction is a spontaneous reaction. Chemical energy is converted into electrical energy.

The reactions occurring during discharge are
tcompartmencathodein
speciesactive
cathodenYMneYM
anodeneMM
c
nn
c
n
aa




At anode: electrons are released to the external circuit.
At cathode: electrons from the external circuit are consumed.
Charging: During charging, reverse reactions take place. The reverse reactions are non-spontaneous
reactions. The battery is connected to an external d.c. power supply. Electrical energy is converted in to
chemical energy.
Example: The reverse of the above reactions occur during charging.
1.17 characteristics of a battery:
1. Voltage: The voltage of a battery mainly depends upon the emf of the cells which constitute the
battery system. The emf of the cell depends on the free energy changes in the overall cell reaction. As
given by Nernst equation,
 
 
 
 reactant
product
QquotientreactiontheisQandEEEwhere
Qlog
nF
RT303.2
EE
M
M
log
nF
RT303.2
EE
nFEG
anode
0
cathode
0
cell
0
0
n
0





Where Ecell =Ecathode- Eanode, and Q is the reaction quotient for the cell reaction at any stage of the reaction.
As it is evident from the above equation, is dependent on
a) Higher the standard electrode potential difference between the cathode and anode, higher is the emf of
the cell and the voltage available from the battery
b) As the temperature increases, emf of the cell decreases.
c) Emf of the cell decreases as the Q increases
2. Current: Current is a measure of the rate at which the battery is discharging. Higher the rate of
spontaneous reaction, higher is the current. Higher the surface area of the electrodes, higher is the rate
of reaction. Current is measured in A.
3. Capacity: Capacity is a measure of the amount of electricity that could be obtained from the fully
charged battery. It is expressed in Ah (ampere hours). It is proportional to the amount of charge in

Coulombs that may be transported from anode to cathode through the external circuit. The charge (C)
in Coulombs is given by the Faraday’s relation:
M
Fnw
C


Where, C is Capacity of battery (in Ah)
W is Weight of the active material
n is number of electrons involved in discharge reaction
F is Faradays constant, 96500 C/mol
M is Molar mass.
4. Electricity storage density: It is the amount of electricity stored in the battery per unit weight of the
battery. i.e. it is the capacity per unit weight. It can be expressed in Coulombs/kg or in Ah/kg. The
weight includes the weight of all components of the battery (i.e. total weight of active material,
electrolyte, terminals etc.)
5. Energy efficiency: The energy efficiency of a rechargeable battery is given by
chargingduringconsumedEnergy
100gdischarginduringreleasedEnergy
efficiencyEnergy%


It holds good only for secondary battery.
6. Cycle Life: Primary batteries are designed for single discharge and secondary batteries can be
chargeable again and again.
The number of charge and discharge cycles that are possible in secondary batteries, before
failure occurs is called cycle life.
The cycle life of batteries must be high for secondary batteries.
7. Shelf life: The duration of storage battery under specified conditions at the end of which a cell or a
battery retains its ability performance lelvel is called shelf life. A good battery should have more shelf
life.
1.18 Zn-air cell (Primary battery, non rechargeable)
Zinc –air battery is a modern and metal air battery. It uses oxygen from the atmosphere and it does not
contribute to the weight of the battery so these batteries offer high energy density.
Construction:

In zinc-air cell, granulated powder of zinc mixed with the electrolyte (KOH) acts as anode material.
Cathode is a carbon-catalyst mixture. The anode can and cathode can act as terminals. The anode material
is separated from the cathode material by an electrolyte absorbent separator. 5M KOH is used as the
electrolyte.
Anode: granulated zinc powder
Cathode: carbon – MnO2catalyst mixture
Electrolyte: 5M KOH
Separator: Polypropylene.
Cell gives a voltage of 1.4V, Energy density 100Wh/Kg.
Cell representation:
air,CKOHZn
When air passed through the cell, zinc is oxidized to ZnO at the anode, during discharge.
Cell reactions:
At anode : Zn + 2OH-
At cathode : 1/2 O2 + H2O +2e-
Over all reaction Zn + 1/2 O2
ZnO + H2O + 2e-
2OH-
ZnO
Uses: Used in Military & radio receivers
Used as a power source in hearing aids.
Used in electronic pagers & various medical devices such as nerve & muscle simulator.
Used in drug impulsion equipment.
1.19 Li-MnO2 cell: (primary battery, non rechargeable)
Li-MnO2 is a primary battery and produces a voltage of about 3V, Energy density 230Wh/Kg.
Lithium has the following advantages:
1. It is light.
2. It has a good electrical conductivity.
3. It has low standard electrode potential (Eo
= -3.05V) .
Construction:
1. The anode is made of lithium metal.
2. The cathode is made of MnO2.
3. A solution of lithium halide in organic solvent acts as the electrolyte.
4. The anode and cathode are separated by a polypropylene separator.
[Lithium halides: LiCl, LiBr, LiAlCl4
Organic solvents: Propylene carbonate and 1, 2 –Dimethoxyethane]

Cell representation : 2MnOsolventsorganicinhalideLithiumLi
Cell reactions:
At anode : Li
At cathode : MnO2 + Li+
+ e-
Over all reaction: Li + MnO2
Li+
+ e-
LiMnO2
LiMnO2
Mn (IV) reduced to Mn( III) & Li+
enters crystal lattice of MnO2
Uses:
Used as memory back up equipments.
Used in watches, calculators, toys, cameras etc.
Used in safety & security devices
1.20 Lithium-ion batteries
The lithium ion batteries are rechargeable battery best suited to mobile devices that requires small size,
light weight and high performance.
In lithium-ion batteries, lithium compounds are used as anode. These batteries are known as re-chargeable
batteries. Therefore, Lithium ion batteries are considered as best than pure Lithium based batteries. It
works on the principal of Intercalation mechanism.
CONSTRUCTION:

1. Li-ion cell has a four-layer structure.
2. Anode: Lithium intercalated graphite/carbon (specialty carbon)
3. Cathode : lithium metal oxide compound such as LiyNiO2 , LiyCoO2 and LiyMnO2
4. Anode current collector -copper foil
5. Cathode current collector- aluminum foil
6. Separator : Polypropylene
7. An electrolyte made with lithium salt [LiPF6] in an organic solvent [propylene carbonate or 1,2 –
dimethoxyethane]..
8. Lithium ion secondary battery depends on an "intercalation" mechanism.
Cell reactions :
During discharge Li ions are dissociated from the anode and migrate across the electrolyte and are
inserted into the crystal structure of the host compound of cathode.
During charging, lithium in positive electrode material is ionized and moves from layer to layer and
inserted into the negative electrode.
At the same time the compensating electrons travel in the external circuit and are accepted by the host to
balance the reaction.
Advantages
1. They have high energy density than other rechargeable batteries
2. They are less weight
3. They produce high voltage out about 4 V as compared with other batteries.
4. They have improved safety, i.e. more resistance to overcharge
5. No liquid electrolyte means they are immune from leaking.
6. Fast charge and discharge rate

Applications:
1. The Li-ion batteries are used in cameras, calculators.
2. They are used in cardiac pacemakers and other implantable device
3. They are used in telecommunication equipment, instruments, portable radios and TVs, pagers
4. They are used to operate laptop computers and mobile phones and aerospace application.
1.21 Nickel-metal hydride battery
[Alkaline storage battery & Secondary battery]
Construction:
1. In these batteries, electrodes are made of porous nickel foil or nickel grid, into which the active
material is packed.
2. Anode: The active material for the anode is a mixture of a metal hydride (such as TiH2, VH2, or ZrH2)
with a hydrogen storage alloy ( such as LaNi5 or TiNi ).
3. Cathode: The active material for cathode is nickel oxy hydroxide, NiO(OH).
4. Electrolyte: An aqueous solution of KOH acts as the electrolyte.
5. Separator: Polypropylene
Cell representation : 2i(OH)N/NiO(OH)/MH/KOH(5M)
The battery produces 1.25 to 1.35V per cell.
Cell reactions:
At anode : MH + OH-
At cathode : NiO(OH) + H2O + e-
Over all reaction: MH + NiO(OH)
M + H2O + e-
Ni(OH)2 + OH-
M + Ni(OH)2
Uses: Used in cellular phones, camcorders and laptop computers.
1.22 Fuel cells:
Fuel cells is defined as a
Galvanic cells in which chemical energy of a fuel directly converted into electrical energy.
Cell can
Cathode
Separator
Anode
Sealing washer
separator
Cell cap
Contact spring

Basic component of fuel cell:
1. Fuel cells consist of electrodes and electrolytes.
2. Catalyst used is embedded in the electrodes.
3. Gaskets are used to prevent the leakage of gases between the electrodes.
Reactions:
At anode: Fuel  Oxidised product + ne-
At cathode: Oxidant + ne-
 Reduced product
Fuel cells are represented as: Fuel /anode/electrolyte/cathode/oxidant
Difference between a battery and a fuel cell:
BATTERIES FUEL CELLS
Batteries are energy storage devices Fuel cells are energy conversion devices.
Secondary batteries are rechargeable Fuel cells are not chargeble.
The reactants and products form an integral
part of batteries.
In fuel cells, continous movement of fuel,
oxidant, and reaction product in and out of cells.
Advantages:
1. High power efficiency approximately 75%.
2. No need of charging.
3. Produces direct current for a long time.
4. No moving parts. Hence wear and tear is eliminated.
5. Harmful products are absent. Hence fuel cells are ecofriendly.
Limitations:
1. Electrodes and electrolytes are expensive.
2. Storage of fuel and oxidant.
3. Gives DC output and should be converted to AC.
1.23 Methanol – Oxygen fuel cell
It is an electroconductive organic fuel cell,
Construction:
1. It consists of anode and cathode made of platinum.
2. Sulphuric acid acts as the electrolyte.
3. A membrane is inserted adjacent to the cathode on the electrolyte side to minimize the diffusion of
methanol into the cathode.
4. Methanol – H2SO4 mixture is circulated through the anode chamber.
5. Pure oxygen is passed through the cathode chamber.

Cell reactions:
At anode : CH3OH + H2O
At cathode : 11/2 O2 + 6H+
+ 6e-
Over all reaction: CH3OH + 11/2 O2
3H2O
CO2 + 2H2O
CO2 + 6H+
+ 6e-
Uses: It is used in large-scale power production.
Used in space vehicles, military & mobile power systems.
Questions:
1. What is battery? Explain the classification of battery.
2. Explain the following battery characteristics:
i. voltage, ii. Current , iii. Capacity, iv. Electricity storage density, v. Energy efficiency ,
vi. Cycle life vii. Shelf life
3. Explain the construction, working & applications of ZINC-AIR battery
4. Explain the construction, working & applications of Li-MnO2 cell
5. Explain the construction, working & applications of Li-Ion battery
6. Explain the construction, working & applications of Ni-MH battery
7. What is a fuel cell? How is it different from the conventional batteries
8. Explain the construction, working & applications of METHANOL-OXYGEN fuel cell
O2CH3OH +
H2SO4
Excess Oxygen and
water
Cathode
Membrane
H2SO4 (electrolyte)
Anode
CO2
CO2

MODULE-2 :
CORROSION
2.1 Definition of corrosion:
Corrosion is defined as the destruction of metals or alloys by the surrounding environment through
chemical or electrochemical reaction.
Example:
i. Formation of rust on the surface of iron,
ii. Formation of green film on the surface of copper.
Corrosion is also called as extractive metallurgy in reverse.
2.2 Types of corrosion:
DRY CORROSION: Dry corrosion occurs due to direct chemical reaction between the metal and the gasses
present in the corrosive environment.
Example: Metals when exposed to dry gasses like O2, SO2, CO2, H2S etc.
WET CORROSION: It is a common type of corrosion of metal in aqueous corrosive environment. This type of
corrosion occurs when the metal comes in contact with a conducting liquid or when two dissimilar metals are
immersed or dipped partly in a solution.
2.3 Electrochemical theory of corrosion:
According to electrochemical theory, when a metal such as iron is exposed to corrosive environment,
following changes occur.
1. Formation of galvanic cells: A large number of tiny galvanic cells with anodic and cathodic regions
are formed.
2. Anodic reaction: Oxidation of metal takes place at the anodic region.
Fe  Fe2+
+ 2 e-
OH- OH-Fe2+
Fe2+
IRON METAL
O2
H2O
Electrons
CATHODEANODE RUST

The Fe2+
ions dissolve, so corrosion takes place at the anodic region.
3. The electrons travel through the metal from the anodic region to cathodic region.
4. Cathodic reaction : Reduction of O2 or H+
takes place at the cathodic region.
In acidic medium,
2H+
+ 2e-
H2
In neutral medium,
O2 + 2H2O + ne-
4OH-
The metal is unaffected at the cathodic region.
5. Fe2+
and OH-
ions travel through the aqueous medium and form corrosion product.
Fe2+
+ 2OH-
Fe(OH)2
6. The corrosion product may undergo further oxidation to form rust.
2Fe(OH)2 + 11/2 O2 + H2O Fe2O3.3H2O
[Yellow rust]
The cathodic and anodic reactions must occur at the same rate. If 𝑖 is the current (corrosion current)
flowing , then the rate of corrosion of iron is given by the equation,
𝑅𝑎 𝑖 =
𝑖
𝑎
𝑤ℎ 𝑖 ℎ𝑎 ℎ 𝑖 𝑎 𝑖 𝑎 𝑎 𝑎𝑦 𝑎
The total current due to the cathodic reaction [ ∑ 𝑖 ] must be equal ,but opposite in sign , to the total
current flowing out due to the anodic reaction [ − ∑ 𝑖 𝑎] .
𝑖 = − ∑ 𝑖 𝑎 = ∑ 𝑖
Reactions at cathodic region: At cathode, the reaction is either a) liberation of hydrogen or b)
absorption of oxygen.
Liberation of hydrogen (in the absence of oxyge Absorption of oxygen(in the presence of oxyge
In acidic medium
2H+
+ 2e-
H2
In acidic medium,
4H+
+ O2 + 4e-
2H2O
In neutral,
2H2O + 2e-
2OH-
+ H2
In neutral,
O2 + 2H2O + ne-
4OH-

2.4 Galvanic Series:
Galvanic series is a series in which the metals and alloys are arranged in the order of their corrosion
tendencies or corrosion resistance.
According to galvanic series,
1. The metal/alloy higher up in the series corrodes faster than the metal/alloys in the bottom of the series.
2. Metals like Ti (placed below Ag in galvanic series but above in emf series) and Al (placed below Zn in
galvanic series but above in emf series) exhibit resistance to corrosion due to phenomenon called Passivation.
3. Passivation: It is the phenomenon of protection of metals against atmospheric corrosion due to
formation of a thin layer of non-porous film of metal oxide. The film forms a barrier between the corrosive
medium and metal [protective layer].
Comparison between Galvanic Series Vs Electrochemical Series:
# Galvanic Series Electrochemical Series
1 It predicts the corrosive tendencies of metal alloys It predicts the relative displacement tendencies
2 Calomel electrode is used as a reference electrode
Standard hydrogen electrode is used as reference
Electrode
3 Positioning of metal or alloy may change Position of metal is fixed. That cannot be changed
4
The metals and alloys are immersed in the sea
water for study
concentration of salts of the same metal that was being used
5
Electrode potentials are measured for both metals
and alloys.
Electrode potentials measured only for metals and non-metals

2.5 Different types of corrosion:
2.6 Differential metal corrosion:
This type of corrosion occurs when two dissimilar metals are in contact with each other and are exposed to
a corrosive environment. The two metals differ in their electrode potentials. The metal with lower
electrode potential acts as anode and the other metal with higher electrode potential acts as cathode. A
galvanic cell develops between the two metals.
The anodic metal undergoes oxidation and gets corroded. A reduction reaction occurs at the cathodic
metal. The cathodic metal does not undergo corrosion.
The reactions may be represented as follows:
Cell reactions:
At anode : M
At cathode : O2 + 2H2O + 4e-
4OH-
(Reduction of oxygen)
Mn+
+ ne-
(Oxidation of metal M)
Higher the potential difference between the anodic and cathodic metals, higher is the rate of corrosion.
Other examples:
1. Steel screws in copper sheet.
2. Steel screws with copper washer.
3. Bolt & nut are made of different metals.
2.7 Differential aeration corrosion:
This type of corrosion occurs when two different parts of the same metal are exposed to different oxygen
concentrations. (e.g. An iron rod partially dipped in water.) The part of the metal which is exposed to
less oxygen concentration acts as anode. The part which is exposed to more oxygen concentration acts as
cathode. The anodic region undergoes corrosion and the cathodic region is unaffected.
Zn metal
[Anode]
Fe metal
[Cathode]
Fe metal
[Anode]
Cu metal
[Cathode]
Fe metal
[Anode]
Sn metal
[Cathode]
Less O2, (Anode)
Water
More O2,
(Cathode)
Iron rod

Cell reactions:
At anode : M
4OH-
Mn+
+ ne-
Other examples:
1. Part of the nail inside the wall undergoes corrosion.
2. When a dirt particle sits on a metal bar, the part under the dirt undergoes corrosion.
3. Partially filled iron tank undergoes corrosion inside water.
2.8 Water line corrosion: This is an example of differential aeration corrosion.
When a steel tank is partially filled with water for a long time, the inner portion of the tank below the
water line is exposed only to dissolve oxygen, whereas, the portion above the water line is exposed to
more oxygen. Thus the portion below the water line acts as anode and undergoes corrosion. The upper
portion acts as cathode and is unaffected.
A distinct brown line is formed just below the water line due to the deposition of rust.
Cell reactions:
At anode : M
4OH-
Mn+
+ ne-
Other example: Ships which remain partially immersed in sea water for a long time undergo water line
corrosion.
2.9 Pitting corrosion: This is an example of differential aeration corrosion.
Rust
Water
More
oxygen,
(Cathode)
Less
Oxygen
(Anode)

When a small dust particle gets deposited on a steel surface, the region below the dust particle is exposed
to less oxygen compared to the remaining part. As a result, the region below the dust particle acts as
anode undergoes corrosion and forms a pit. The remaining region of the metal acts as cathode and is
unaffected.
Cell reactions:
At anode : M
4OH-
Mn+
+ ne-
Formation of a small anodic area and a large cathodic area results in intense corrosion below the dust
particle.
2.10 Stress corrosion: In a metallic structure, if there is a portion under stress, it will
act as anode and rest part of the structure will act as cathode. It is now a galvanic system and hence
anodic part which is small in area will corrode more.
Example: Caustic embrittlement in boilers -
1. It is a type of boiler corrosion which makes boiler material brittle. This is caused by using highly alkaline water
in the boiler, most commonly in high pressure boiler. During lime soda process, free Na2CO3 is usually present in
small proportion in the softened water.
2. Na2CO3 in high pressure boilers decomposes to give sodium hydroxide and carbon dioxide. This makes boiler
water caustic.
Na2CO3+H2O2NaOH+CO2
3. This causes embrittlement of boiler parts, particularly stressed parts like bends, joints etc.
4. The water containing NaOH flows into the minute hair-cracks, in the inner wall of boiler, by capillary action.
Here, water evaporates and the concentration of NaOH increases progressively. When the concentration of NaOH
increases to 10%, caustic soda attacks the surrounding areas, thereby dissolving iron of boiler wall as sodium-
ferroate. This causes embrittlement of boiler wall at stressed parts like bends, joints, etc.
3Na2FeO2 + 3H2O Fe3O4 + H2 + 6NaOH
Addition of Na2SO4 and phosphates to boiler water prevents caustic cracking.
2.11 Factors affecting the rate of corrosion:
1. Nature of the metal: Metals with lower electrode potentials are more reactive and are more
susceptible to corrosion. For example, elements such as Mg and Zn, which have low electrode potentials,
Cathode
Boiler
Soft water =
Very dilute NaOH
Anode

are highly susceptible to corrosion. Noble metal such as gold and platinum, which have higher electrode
potentials, are less susceptible to corrosion.
Exceptions: Metals and alloys which show passivity are exceptions for this general trend. Such metals
form a protective coating on the surface which prevents corrosion.
2. Nature of corrosion product:
If the corrosion product [OXIDE LAYER] is insoluble, stable and non-porous, then it acts as a protective
film which prevents further corrosion. The film acts as a barrier between the fresh metal surface and the
corrosive environment.
On the other hand, if the corrosion product is soluble, unstable and porous, then the corrosion process
continues even after the formation of corrosion product.
Example: Aluminium, titanium and chromium form a protective film of metal oxide on the surface.
Stainless steel forms a protective film of Cr2O3 on the surface. But in the case of Zn and Fe, the
corrosion products formed do not have protective value.
3. Difference in potential between anodic and cathodic regions: Larger the potential
difference between the anodic and cathodic regions, higher is the rate of corrosion. For example, the
potential difference between iron and copper is 0.78 V, and between iron and tin is 0.3 V. Therefore,
corrosion is faster when iron is in contact with copper.
The use of dissimilar metals should be avoided wherever possible. Otherwise, the anodic metal gets
corroded.
4. Anodic and cathodic areas:
Smaller the anodic area and larger the cathodic area exposed to corrosive atmosphere, more intense and
faster is the corrosion occurring at anode.
When anode is smaller and cathode region is larger the liberated electrons at anode are rapidly consumed.
If the cathode is smaller and reverse process takes place, decrease rate of corrosion. .
𝑪 𝑹𝒂 =
𝑪𝒂 𝒂 𝒂
𝑨 𝒂 𝒂
Larger the anodic area and smaller the cathodic area, decreases the rate of corrosion.
Ex: A small steel pipe fitted to copper tank, increases the rate of corrosion.
5. pH
of the medium: Rate of corrosion increases with decrease in pH.
a) Metals do not undergo corrosion at pH
greater than 10. This is due to the formation of protective coating
of hydrous oxides of iron.
b) Between pH
10 and 3, the presence of oxygen is essential for corrosion.
c) If the pH
is less than 3, corrosion occurs even in the absence of oxygen.

6. Temperature: Higher the temperature, higher is the rate of corrosion.
Increase in temperature increases the ionic conductivity of the corrosive medium. This also contributes to
the increase in corrosion rate.
7. Conductance: As the conductivity of the corrosion medium increases, the corrosion rate also
increases. Higher the conductivity of the medium, faster the ions can migrate between the anodic and
cathodic regions of the corrosion cell, in turn, faster will be the exchange of electrons at the electrode
surfaces. This facilitates higher corrosion rate.
2.12 Corrosion control
2.12 Anodizing (Anodizing of aluminum):
When aluminum metal is made anodic in an electrolytic bath with sulphuric acid or chromic acid as
the electrolyte, a thin layer of aluminium oxide (Al2O3) is formed on the surface. This process is called
anodizing of aluminium or anodic oxidation of aluminum.
Anodizing is carried out as follows:
The article is made as anode and steel or copper is made as cathode. The electrodes are dipped in a
solution of 5 – 10% chromic acid, the temperature of the bath is maintained at 350
c. A potential is
applied and gradually increased from 0 to 40V during the first 10 min. Anodizing is carried out for 20 min
at 40V. After 20 min, the potential is increased
to 50V and held at this potential for 5min. An
opaque layer of 2-8 µm thickness is obtained.
Anodized aluminium is exposed to a corrosive
environment, the Al2O3 layer on the surface
acts as a protective coating. Hence corrosion is
prevented.
Other metals such as Mg, Ti etc. can also be
anodized.
(Note: On anodizing, Al2O3 is formed on the surface as a porous layer. The layer may be made compact
by sealing, which involves heating with boiling water or steam. During sealing, Al2O3 is converted into
Al2O3.H2O which occupies higher volume. Therefore, the pores are sealed.)
Applications: Anodized aluminium is used in computer hardware, roofs, floor, ceilings, curtains, escalators
and commercial buildings.
Electrolyte 5-10% of chromic
Temperature 350
c
Thickness of oxide layer 2-8µm
Dc Power
Al2O3 H2CrO4
Cathode
Anode Al

2.13 Phosphating: Phosphating is a process of Conversion of surface metal atoms into
their phosphates by chemical or electrochemical reactions is called phosphating.
The phosphating bath contains three essential components:
(i) free phosphoric acid,
(ii) a metal phosphate such as Fe, Mn phosphate and
(iii) An accelerator such as H2O2, nitrites, nitrates.
(iv) Temperature – 35o
C
(v) pH – 1.8-3.2
Phosphating not only improves the corrosion resistance but also imparts good paint adhesion quality to the surface.
Applications: Phosphate coating is given as an under layer [primer coat] before painting the car bodies,
refrigerators and washing machines.
2.14 Metal coatings:
2.15 Anodic metal coating: It is a process of coating of base metals with anodic
metals such as Zn, Al, Mg, and Cd etc.
Example: Galvanizing
2.15 Galvanizing of iron : Galvanizing is the process of coating a metal surface such as
iron with zinc metal.
Galvanization is carried out by hot dipping method. It involves the following steps.
i) The metal surface is washed with dilute sulphuric acid.(Pickling process) to remove ant dirt ,rust on the surface.
[descaling].
ii) Oil, grease is removed by washing organic solvents (CCl4, toluene) [degreasing].
iii)Finally, the article is washed with water and air-dried.
iv)The article is then dipped in a bath of molten zinc. (Molten zinc is covered with a flux of ammonium chloride to
prevent the oxidation of molten zinc.).
v) The excess zinc on the surface is removed by passing through a pair of hot rollers.
Application: Galvanization of iron is carried out to produce roofing sheets, fencing wire, buckets, bolts,
nuts, pipes etc.
Iron
sheet
Dil .H2SO4
Organic
Solvent
Water Molten Zinc +
NH4Cl (flux)
At 420 -5000C
Air drier
Pair of hot
rollers
Excess of Zn
Galvanized
sheet

2.16 Cathodic metal coating : It is a process of coating of base metals with
cathodic metals such as Sn , Ni , Cr and Cu etc.
Example: Tinning
2.16 Tinning: Tinning is the process of coating the surface of a base metal (such as iron) with
tin. Tinning of iron metal is an example of cathodic metal coating on an anodic base metal.
Tinning of iron is carried out by hot dipping method. It involves the following steps.
i) The metal surface is washed with dilute sulphuric acid.(Pickling process) to remove any dirt ,rust on the
surface. [descaling].
ii) Oil, grease is removed by washing organic solvents (CCl4, toluene) [degreasing].
iii) Finally, the article is washed with water and air-dried.
iv) It is then passed through molten zinc chloride flux. The flux helps the molten tin to adhere strongly on the
surface.
v) It is then dipped in a bath of molten tin.
vi) The coated tin is immersed in palm oil. The oil prevents the oxidation of tin coating.
vii) The excess zinc on the surface is removed by passing through a pair of hot rollers.
Applications: Tin-coated steel is used for manufacturing containers.
(Note: Copper utensils are coated with tin to prevent contamination of food with poisonous copper salts.)
2.17 Cathodic protection:-
In cathodic protection, the metal to be protected is completely converted into a cathode. Since cathodes
do not undergo corrosion, the metal is protected against corrosion.
Iron
sheet
Dil .H2SO4 Organi
c
Water
Air drier
Pair of
hot
Rollers
Excess of Sn
ZnCl2
flux
Palm oil
Molten tin

2.18 Sacrificial anode method:
In sacrificial anode method, the metal to be protected is electrically connected to a more active metal. For
example, when steel is to be protected, it may be connected to a block of Mg or Zn. In such a situation,
steel acts as cathode and is unaffected. Mg and Zn act as anode and undergo sacrificial corrosion. When
the sacrificial anode gets exhausted, it is replaced with new ones.
Other examples: Mg bars are fixed to the sides of ships to act as sacrificial anode.
Mg blocks are connected to burried pipe lines.
2.19 Impressed current method (impressed voltage
method):
In impressed current method, the metal to be protected is connected to the negative terminal of an external
d.c. power supply. The positive terminal is connected to an inert electrode such as graphite. Under these
conditions, the metal acts as cathode and hence does not undergo corrosion. The inert electrode acts as
anode; but it does not undergo corrosion because it is inert.
Zn or Mg block

2.20 Questions:
1. Describe electrochemical theory of corrosion with iron as example.
2. Define corrosion.
3. Describe differential metal corrosion.
4. Explain differential aeration corrosion.
5. Describe pitting corrosion
6. Explain waterline corrosion.
7. Describe stress corrosion [caustic embrittlement in boilers].
8. Describe the effect of following factors on the rate of corrosion: (i) Nature of metal, (ii) Nature of
corrosion product, (iii) Difference in potential between anodic and cathodic regions.(iv) Anodic and
cathodic areas
9. Describe the effect of pH
, temperature & conductance on the rate of corrosion.
10. What is anodizing? Describe anodizing of aluminium.
11. Explain phosphating.
12. What is galvanizing? Describe galvanizing of iron.
13. Explain tinning.
14. Explain cathodic protection by sacrificial anode method and ICCP method

MODULE-2 :
Metal finishing
2.21 Definition of metal finishing:
Metal finishing is the process of deposition of a layer of one metal on the surface of substrate
(metal, plastic etc) or the process of conversion of a surface layer of atoms on a metal into an oxide
film. (Note: Metal finishing is the process of surface modification of a metal)
2.22 Technological importance of metal finishing:
Importance of metal finishing are,
 A decorative appearance.
 To increase the corrosion resistance
 To increase thermal resistance
 To increase optical reflectivity.
 To impart electrical and thermal properties such as semi-conduction and fire
resistance.
 To impart hardness & solderability
 To provide electrical and thermal conducting surface
 Manufacturing electrical and electronic components such as contacts, PCB, capacitors
& contacts etc.
 In electroforming (to manufacture metal articles entirely by electroplating)
 In electrotyping (to produce finely engraved dies or similar finely divided articles such
as gramophone records)
 In electrochemical machining, polishing and etching.
 To build up material or restoration
2.23 Electroplating:
Definition: Electroplating is the process of electrolytic deposition of a metal on the surface of
another metal, alloy or conductor by the process of electrolysis.
The three important factors governing the process of electrolysis,
i. Polarization
ii. Decomposition potential
iii.Over voltage
2.24 Polarization:
Definition: Polarization is defined as a process where there is a variation of electrode potential due to
inadequate [slow] supply of ionic species from the bulk of the solution to the electrode surface.

Polarization is an electrode phenomenon,
The electrode potential is given by the Nernst’s equation,
Where E0
= standard electrode potential and [ Mn+
] is the metal ion concentration surrounding the electrode
surface at equilibrium.
Explanation: Consider an electrolytic cell under operation. When current is being passed, positive ions are
produced at the anode and are consumed at the cathode. If the diffusion of ions in the electrolyte is slow,
there will be an accumulation of positive ions in the vicinity of anode. Similarly, there will be a depletion of
ions in the vicinity of cathode. Under these conditions, the anode and cathode are said to be polarized. This
type of polarization is known as concentration polarization.
Factors affecting the electrode polarization:
1. Nature of the electrode [size, shape & composition]
2. Electrolyte concentration
3. Temperature
4. Rate of stirring of the electrolyte
5. Products formed at the electrode
Large electrode surface, low [Mn+
] concentration, continuous stirring decreases polarization
2.25 Decomposition potential [Ed]
Definition: Decomposition potential is defined as the minimum voltage that must be applied in
order to carry out continuous electrolysis of an electrolyte.
The decomposition potential is determined using an electrolytic cell as shown in figure:
]n[Mlog
n
0591.00E
cell
E 
A graph of variation of current w. r. to applied potential

Example: In the electrolysis of water, a pair of platinum electrodes immersed in a solution of an acid.
It is found experimentally that a potential of about 1.7V must be applied to the cell before there sets in
a continuous evolution of H2 and O2 .The voltage at which the current increases suddenly is called Ed
of the electrolyte.
2.26 Over voltage (over potential) (η)
Definition: Over voltage is defined as the excess voltage that has to be applied above the theoretical
decomposition potential to start the electrolysis.
η = [Ed] experimental -[Ed] theoretical
Example: For electrolysis of water using smooth platinum electrodes,
The theoretical decomposition potential using Pt electrode is 1.23 V.
The experimental decomposition potential using smooth platinum electrode is 1.7 V.
η = 1.7-1.23 = 0.47V
Factors affecting the over voltage value:
1. Nature of the electrode.
2. Nature of the product formed at the electrode.
3. Current density (i.e. current per unit area of the electrode surface.)
4. Temperature
5. Rate of stirring.
2.27 Principal components of an electroplating process:
The principal components are shown in the following figure.
The main components are:
1. Electroplating bath: It contains a suitable
salt solution of the metal being plated. It also
contains other additives.
2. Anode: It may be a rod or pellets of the
metal being plated. It may be an inert
electrode. It should be electrically conducting.
3. Cathode: It is the article to be plated. It
should have an electrically conducting surface.
4. Inert vessel: It contains above mentioned
materials. It may be a vessel made of rubber
lined steel, plastic concrete or wood.
5. D.C. power supply: The positive terminal
of the power supply is connected to the anode and the negative terminal is connected to the cathode.

2.28 Effect of plating variables on the property of electrodeposit:
1.Current density: Current per unit area of the electrode surface. [Amperes/cm2
].
 At low current density, a bright, fine grained crystalline deposit is obtained but the rate of deposition
is slow.
 At high current density, hydrogen evolution occurs at the cathode, a burnt and spongy deposit
results.
In general, for a particular bath, the optimum current density is experimentally determined and
applied.
Optimum current density ranges from 10 to70 mA/cm2
2. Concentration of metal ion:
 At high concentration of electrolyte, mass transfer increases leads to poor deposit.
 At low concentration, crystal size decreases and results in fine deposit. Therefore, the free metal ion
concentration is kept low.
Optimum molar concentration of an electrolyte maintained is 1-3mol/dm3
 A low metal ion concentration may be achieved by the addition of a compound with a common ion
(e.g. addition of H2SO4 to CuSO4)
3. Complexing agents:
 Complexing agents are used to maintain a low metal ion concentration, results in fine deposit.
 Complexing agents are also used to improve the throwing power of the bath. Higher the throwing
power, more uniform is the deposit.
(e.g. addition of NaCN to CuCN to get low concentration of Cu+
)
4. Throwing power of a bath: is a “Capacity of plating bath to give a uniform deposit even
on an irregularly shaped object.”
Measurement of throwing power: Haring-Blum Cell
- +
d1 d2 Cathode2
Cathode1
Electrolytic
solution

1. It consists of two electrodes and an anode at the center. The cathodes are at different distances d1
and d2 from anode [let d1>d2]
2. The process of electroplating is carried out and the weights [w1 & w2] of deposits at cathodes [1
&2] are noted.
When w1= w2 i.e. amount deposited is same irrespective of the placement of the electrode, then
throwing power is considered very good (100%).
When the calculated throwing power is – 100% then it is considered as very poor.
Factors affecting the throwing power of bath:
1. Concentration of electrolyte
2. Conductance of solution
3. Additives
5. pH
of an electrolytic bath:
 At low pH
values, liberation of hydrogen occurs at the cathode resulting in a burnt deposit.
2H+
+ 2e-
H2
 At high pH
values, the cathode surface gets coated with insoluble hydroxides.
2)OH(MOH2M  
Therefore, for most of the plating processes, a pH
range of 4-8 is optimum.
 The desired pH
is maintained using suitable buffers. (e.g. phosphate buffer in gold plating)
6. Temperature:
 Increase in temperature increases the conductivity, increases the mobility of ions, and decreases the
polarization.
 However, too high a temperature may lead to evolution of hydrogen at the cathode, results in burnt
deposit.
 Therefore, a moderate temperature range of 35 – 60o
C is used for most of the plating processes.
7. Organic additives: To improve the quality of electrodeposit, certain organic compounds are
added to the electrolytic bath.
These are a) brighteners, b) levellers, c) structure modifiers and d) wetting agents.
a. Brighteners: Brighteners are added to get bright deposits and light falling on the metal
surface gets reflected.
w1
w2
=y,
d2
d1
=xWhere
2)-y+(x
100×y)-(x
solutionbaththeofpowerthrowing% 

Example: Aromatic sulphones, sulphonates, thiourea etc. in Ni plating.
(Note: When the grain size of the electrodeposit is lower than the wave length of the incident light,
the light gets reflected, but not scattered. Thus the deposit appears bright.)
b. Levellers: Levellers are added to get a level [uniform] deposit. Levellers get adsorbed at
places where rapid or excessive deposition is taking place, thus preventing the excessive growth in
those places.
Example: Sodium allyl sulphonate in Ni plating.
c.Structure modifiers (Stress relievers): Structure modifiers are added to change the orientation of
the crystals with respect to surface of substrate and reduce internal stress.
Example: Saccharin.
d. Wetting agents: Wetting gents are added to remove any hydrogen sticking to the cathode
surface. Thus they prevent hydrogen embrittlement of the deposit.
Example: Sodium lauryl sulphate.
2.29 Electroplating of chromium
 The surface of the object is subjected to descaling [washing with an acid] and
 Degreasing [washing with organic solvent].
 Finally, the surface is washed with deionized water. Then, chromium plating is done under the
following conditions.
# Particulars Decorative Cr-plating Hard Cr-plating
1 Plating bath composition
Chromic acid (CrO3) +
H2SO4 in the
weight ratio 100 : 1
Chromic acid (CrO3) +
H2SO4 in the
weight ratio 100 : 1
2 Operating temperature 45-55 o
C 43-66 o
C
3 Current density 100 – 200 mA/cm2
215 – 430 mA/cm2
4 Current efficiency 8 – 12 % 10-15%
5 Anode
Insoluble anode: Pb-Sb or
Pb-Sn alloy coated with PbO2.
Insoluble anode: Pb-Sb or
Pb-Sn alloy coated with PbO2.
6 Cathode Object to be plated Object to be plated
7 Anodic reaction  2e
2
O
2
1
2HO
2
H
oxygen,ofl i berati on
 2e
2
O
2
1
2HO
2
H
oxygen,ofl i berati on
8 Cathodic reaction 
 

3S O6
CrCr
2
4 
 

3S O6
CrCr
2
4

 In chromic acid, chromium is present in 6+ oxidation state. It is first reduced to 3+ state by a
complex anodic reaction in the presence of sulphate ions.

 

3S O6
CrCr
2
4
 The Cr3+
then gets reduced to Cr on the substrate surface.
Cr3eCr3
 
For a good deposit, the Cr3+
concentration must be low.
 The PbO2 oxidizes a part of Cr3+
to Cr6+
, thus reducing the concentration of Cr3+
.

  6P bO
Cr3Cr 2
During Cr coating, Cr rods are not used as anodes because:
1. In acidic solutions, chromium may undergo passivation.
2. Chromium anodes increase the Cr3+
concentration.
2.30 Electroplating of Nickel by watt’s method :
 The surface of the object is subjected to descaling [washing with an acid] and
 Degreasing [washing with organic solvent].
 Finally, the surface is washed with deionized water. Then, chromium plating is done under the
following conditions.
Cr3eCr3
 
Cr3eCr3
 
9 pH 2-4 2-4
10 Applications
Used in corrosion resistant coating.
Used to give decorative finish on
automobiles & surgical instruments
1. Extensively used in industrial
& engineering applications.
# Particulars Nickel plating (watt’s method )
1 Plating bath composition 250g of NiSO4 + 45g of NiCl2+30g of boric acid
2 Operating temperature 25-65o
C
3 Current density 10-60A/ft2
4 Current efficiency 95-100 %
5 pH 4-4.5
6 Anode Nickel pellets or nickel pieces

2.31 Electroless plating:
Definition of electroless plating: Electroless plating is a method of depositing a metal over a catalytically
active surface of the substrate by using suitable reducing agent without using electrical energy.
product.oxidized+MagentReducing+M +n

 The catalytic metals such as Fe, Ni, CO, Rh, Pd, Al etc do not require any surface preparation before
electroless plating.
 But a Non-catalytic metal such as Cu, Brass, and Ag etc needs activation. This is done by dipping
the base metals in PdCl2 (Palladium chloride) in HCl.
 Non – Conductors like glass, insulators, plastics, ceramics etcare first activated in a solution of SnCl2
in HCl. After rinsing, it is immersed in a solution of PdCl2 in HCl.
2.32 Distinction between electroplating and electroless
plating:
Property Electroplating Electroless plating
Driving force Power supply Autocatalytic redox reaction
Anode Separate anode Catalytic surface of the substrate
Cathode Article to be plated Article to be plated ( with a catalytic surface)
Reducing agent Electrons Chemical reagent
Reactions
MneM
neMM
n
n




product.oxidized+MagentReducing+M +n

Applicability Only conductors Conductors, semiconductors & insulator
Nature of deposit Not satisfactory for intricate parts Satisfactory for all parts
7 Cathode Object to be plated
8 Anodic reaction 
 2eNiNi 2
9 Cathodic reaction Ni2eNi2
 
10 Additives Saccharin , coumarin, aromatic sulphonaamide
11 Applications
As an undercoat for Cr plating, brass,gold & rhodium p
Decorative mirror finish
Black nickel plating is used for making name plate,
type writer parts, camera components,optical &
electrical instruments

2.33 Electroless plating of Copper
 Before electroless plating, the surface is cleaned thoroughly.
 Insulators such as plastics and printed circuit boards are activated by dipping first in stannous
chloride (SnCl2) and then in palladium chloride (PdCl2).
 Then, the electroless plating is done under the following conditions:
# Particulars Electroless plating of copper
1 Plating bath solution CuSO4 [12g/lt]
2 Reducing agent Formaldehyde (HCHO)
3 Complexing agent EDTA
4 Buffer Sodium hydroxide and Rochelle salt
(Na-K-tartrate)
5 pH 11
6 Temperature 250
C
CuHO2H2HCOOCu4OH2HCHO:reactionOverall
Cu2eCu:Cathode
2eHO2H2HCOO4OH2HCHO:Anode
22
-2-
-2
-
22
--





Formaldehyde and copper sulphate are added to the plating bath periodically.
Applications: 1. Used for metalizing printed circuit boards, Used to produce through-hole
connections.
2.34 Through-hole connection is PCB’s:
For PCB’s with double sided circuits, through-hole connection is required. The through-hole
connection is made by electroless plating technique. Preparation of PCB by electroless plating:
1. The base material is made up of glass reinforced plastic [GRP’S] or epoxy polymer.
2. The base material which is double sided, is electroplated with copper
3. Selected areas are protected by photoresist.
4. The rest of copper is removed by etching to produce circuit pattern or track
5. The connection between two sides is made by drilling hole followed by plating-through-holes by
electroless plating.

2.35 Questions:
1. What is metal finishing? Explain technological importance of metal finishing.
2. What is electroplating? Explain the following terms
a. Polarization b. Decomposition potential c. Overvoltage
3. Explain the following plating variables affects nature of electro deposit
a. current density b. temperature & pH c. concentration of the electrolyte
d. throwing power of an electrolytic bath d. organic additives
4. Explain electroplating of (decorative & hard) chromium & mention its application.
5. Explain electroplating of Nickel by watt’s method
6. What is electroless plating? What are the differences between electroplating & electroless plating
7. Explain electroless plating of copper in the manufacturer of PCB’s

MODULE-3:
Chemical fuels & solar cells
3.0 Definition of a chemical fuel: A chemical fuel is a substance, which produces
a significant amount of heat energy and light energy when burnt in air or oxygen.
3.1 Classification of chemical fuels:
Chemical fuels are classified as primary and secondary fuels. Fuels, which occur in nature, are called primary
fuels.
Fuels, which are derived from primary fuels, are called secondary fuels.
Chemical fuels are further classified as solids, liquids and gases. A complete classification of fuels with
examples is shown in the following Table.
Physical state Primary fuels Secondary fuels
Solid Wood, coal Charcoal, coke
Liquid Petroleum Petrol, diesel, kerosene
Gas Natural Gas LPG, CNG, Water gas, producer gas
Importance of hydrocarbons as fuels: Fossil fuels contain mainly hydrocarbons. These hydrocarbons are
important sources of energy in daily life. Hydrocarbons are used as energy sources in cooking, lighting,
automobiles, production of electricity in thermal power plants etc. These hydrocarbon fuels meet 80% of the
world’s energy demand. Thus hydrocarbons are important sources of energy.
3.2 Definition of calorific value of a fuel [Gross calorific value]:It is defined as
the amount of heat liberated when unit quantity (1 kg or 1 m3
) of a fuel is completely burnt in air or oxygen
and the products of combustion are cooled to room temperature.

3.3 Definition of net calorific value: It is defined as the amount of heat released when unit
quantity of a fuel is completely burnt in air or oxygen and the products of combustion are let off into the
atmosphere.
S. I. unit of calorific value: For solids, calorific value is expressed in J kg-1
(Joules per kg). For gaseous fuels
it is expressed in J m-3
(Joules / m3
).
3.4 Determination of calorific value of a solid fuel using
Bomb Calorimeter:
Principle: A known mass of the solid sample is burnt in excess oxygen. The surrounding water and the
calorimeter absorb the heat liberated. Thus the heat liberated by the fuel is equal to the heat absorbed by the
water and the calorimeter.
Construction: The bomb calorimeter consists of a stainless steel vessel with an airtight lid. This vessel is
called bomb. The bomb has an inlet valve for providing oxygen atmosphere inside the bomb and an electrical
ignition coil for starting of combustion of fuel. The bomb is placed in an insulated copper calorimeter. The
calorimeter has a mechanical stirrer for dissipation of heat and a thermometer for reading the temperature.
Working: A known mass of the solid fuel is placed in a crucible. The crucible is placed inside the bomb. The
lid is closed tightly. The bomb is placed inside a copper calorimeter. A known mass of water is taken in the
calorimeter. The bomb is filled with oxygen at a pressure of 25-30 atm. The temperature t1 in the thermometer is
noted.
On passing an electric current through the ignition coil, the fuel gets ignited. The fuel burns liberating heat. The
water is continuously stirred using the stirrer. The maximum temperature attained by the water, t2 , is noted.
Observation and calculations:
b) Calculation of G C V

Gross calorific value (G C V) =
 
m
tsww  21
kJ kg-1
Where
w = w1+ w2
= mass of water in the calorimeter, in kg + water equivalent of the calorimeter, in kg
s = specific heat of water, in kJ kg-1 o
C-1
t = t2-t1 = rise in temperature, in o
C
m = mass of the fuel, in kg
(Note: If the mass of fuel is given in grams, convert that into kg. For example, 0.2 g = 0.2  10-3
kg. If specific
heat of water is given in J kg-1o
C-1
, calorific value will be in J kg-1
. If the specific heat is given in kJ kg-1o
C-1
,
then the calorific value will be in kJ kg-1
.)
(Note: Specific heat of water is the amount of heat energy required to increase the temperature of one kg of
water by one degree C.)
b) Calculation of N C V
NCV = GCV-0.09  % H Latent Heat of steam
……..kJ Kg-1
NCV = GCV-0.09  % H  2454  103
kJ Kg-1
3.5 Numerical on GCV & NCV:
Problem 1. Calculate the calorific value of a sample of coal from the following data:
Mass of Coal = 0.6 g
Mass of water + water equivalent of calorimeter = 2200 g
Specific heat of water = 4.187 kJ kg-1o
C-1
Rise in temperature = 3o
C
Solution:
(Note: In solving the problem, follow the steps given below:
1. Write the given quantities and convert them into appropriate units.
2. Write the equation.
3. Substitute the values.
4. Simplify using calculator if necessary.
5. Write the answer.
6. Write the units.)
Given: m = 0.6 g = 0.6  10-3
kg
w1 + w2 = 2200 g = 2.2 kg
s = 4.187 kJ kg-1o
C-1
t = 3o
C
Gross calorific value =
 
m
tsww  21
kJ kg-1

= 3
106.0
3187.42.2



=
46057 kJ/kg
Problem 2. A 0.85 g of coal sample (carbon 90 %, H2 5%, and ash 5% ) was subjected to combustion in
a bomb calorimeter. Mass of water taken in the calorimeter was 2000 g and the water equivalent of
calorimeter was 600 g. The rise in temperature was 3.5 o
C. Calculate the gross and net calorific value of
the sample. (Given, specific heat of water = 4.187 kJ kg-1o
C-1
and latent heat of steam = 2454 kJ kg-1
)
Solution: Given m = 0.85 g = 0.85  10-3
kg
% of hydrogen = 5%
w1 = 2000 g = 2 kg
w2= 600 g = 0.6 kg
t = 3.5 o
C
s = 4.187 kJ kg-1o
C-1
L = 2454 kJ kg-1
a) Gross C.V. =
 
m
tsww  21
=
 
3
1085.0
5.3187.46.02



=
44825kJ kg-1
b) Calculation of N C V
NCV = GCV-0.09  %H Latent Heat of steam
……..kJ Kg-1
=44825 -0.09  5 2454 =44825 - 1104.3
=43720kJ kg-1
(Note: Latent heat of steam is the amount of heat energy liberated when one kg of steam is converted into one
kg liquid water.)
Problem 3. On burning 0.75g of a solid fuel in a bomb calorimeter the temperature of 2.5kg of water is
increased from 240
C to 280
C the water equivalent of calorimeter and latent heat of steam are 0.485 Kg
and 4.2X587 KJ/Kgrespectively , specific heat of water is 4.2KJ/Kg/0
C, H2 2.5%.
Solution: Given
m = 0.75 g = 0.75  10-3
kg
w1+W2 = (2.5+0.485) kg = 2.985 kg
t = t2-t1=28-24=4 o
C
s = 4.2 kJ kg-1o
C-1

Engineering chemistry[As per New CBCS Scheme for I/II semester BE courses of VTU, bengaluru]

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