a concise textbook on - himalaya publishing house · 2018-10-17 · it gives us immense pleasure in...

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A Concise Textbook on

ENGINEERINGCHEMISTRY

(For VTU Choice Based Credit System Syllabus 2015)

Dr. C. MuthukumarProfessor and Head, Dept. of Chemistry, M.V.J. College of Engineering, Bangalore.

Dr. Siju N. AntonyAssociate Professor of Chemistry, M.V.J. College of Engineering, Bangalore.

Dr. Manjunatha D.H.Assistant Professor of Chemistry, MS Ramaiah Institute of Technology, Bangalore

ISO 9001:2008 CERTIFIED

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© AuthorsNo part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by anymeans, electronic, mechanical, photocopying, recording and/or otherwise without the prior written permission of thepublisher.

First Edition : 2016

Published by : Mrs. Meena Pandey for Himalaya Publishing House Pvt. Ltd.,“Ramdoot”, Dr. Bhalerao Marg, Girgaon, Mumbai - 400 004.Phone: 022-23860170/23863863, Fax: 022-23877178E-mail: [email protected]; Website: www.himpub.com

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DTP by : Priyanka M.

Printed at : M/s Sri Sai Art Printer Hyderabad. On behalf of HPH.

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Preface

Engineering has stretched into different frontiers of our lives promising ever increasingbundles of opportunities and challenges. Engineering Chemistry plays an inevitable role inproviding a fundamental as well as broad knowledge of theoretical, applied and experimentalchemistry to the budding engineers to enable them to embark on professional careers of theirchoice.

It gives us immense pleasure in bringing forward this book entitled “A ConciseTextbook on Engineering Chemistry” which comprises of five modules as per the latestVisvesvaraya Technological University (VTU) Choice Based Credit System (CBCS)Syllabus 2015. This book is intended to cater to the needs and aspirations of both Ist and IInd

semester engineering students, and the faculty concerned.

The distinct features of the book are:

Attractive pictures or cartoons which help students to learn with fun

Simple and lucid style of writing

Linking of topics and sizing according to the scheme of evaluation followed by VTU

Highlights of latest developments on relevant topics in appendix

Solved and unsolved problems to enhance problem solving skills

Points to remember at the end of each chapter

Review questions based on recent VTU question papers

All these discrete characteristics will enable students to achieve higher levels oflearning.

We highly appreciate constructive comments and suggestions for improvement.

Authors

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Acknowledgements

It is by the love and blessings of the Almighty that we are able to complete this booksuccessfully hitherto and present this piece of work for which, we are eternally indebted.

We are greatly indebted to the management of M.V.J. College of Engineering,Channasandra, Near ITPB, Bangalore – 67 for the encouragement and also for providing thenecessary facilities.

The authors have a great pleasure in thanking the publisher, Himalaya Publishing HousePvt. Ltd., Mumbai – 400 004 for inviting the authors to write this concise textbook onEngineering Chemistry.

Writing a technical book needs deep knowledge and intuition into the subject along withreferences from a host of relevant sources followed by consultation with peers from the field.

The authors are thankful to following academicians for direct and indirect support inaccomplishing this book.

Prof. M. Brinda, Vice Principal, MVJCE, Bangalore; Prof. K. Thyagarajan, Director,Research and Development, MVJCE, Bangalore; Dr. Ramdas Balan, Head, Dept. of Physics,MVJCE, Bangalore; Dr. Latha Shanmugam, Head, Dept. of MCA, MVJCE, Bangalore;Dr. A.K. Satheesh Babu, Registrar, MVJCE, Bangalore; Dr. H.R. Shivakumar, Vice Principal,KVGCE, Sullia; Dr. Prasad P., Head, Dept. of Nanotechnology, SITM, Mangalore; Dr. SrabaniGhosh, Associate Professor, Dept. of Chemistry, MVJCE, Bangalore; Dr. T.M. Veeresh,Associate Professor, Dept. of Chemistry, PDIT, Hospet; Dr. R.K. Patil, Head, Dept. ofChemistry, KLECET, Chikkodi; Mrs. Preethi G., Assistant Professor, Dept. of Chemistry,MVJCE, Bangalore; Dr. Fazlur Rahaman, Head, Dept. of Chemistry, CMRIT, Bangalore;Dr. H.N. Gayathri, Dept. of Chemistry, OCE, Bangalore; Dr. A.K. Shukla, Dept. of Chemistry,EPCE, Bangalore; Mrs. Rashmi Rani Padhy, Assistant Professor, Dept. of Chemistry, MVJCE,Bangalore; Mrs. Swathi Lal, Assistant Professor, Dept. of Chemistry, MVJCE, Bangalore;Dr. Hemakumar, Head, Dept. of Chemistry, CaIT, Bangalore; Mr. Parashuram L., AssistantProfessor, New Horizon College of Engg., Bangalore; Mrs. Surekha M., Associate Professor,Dept. of Chemistry, KVGCE, Sullia; Dr. Irfan N. Shaikh, Associate Professor, SECABIT,Bijapur; Ms. Ramya K.B., Assistant Professor, Dept. of Chemistry, MVJCE, Bangalore;Ms. Swathi K.N., Assistant Professor, Dept. of Chemistry, MVJCE, Bangalore;Dr. Shivashankaraiah, Associate Professor, Dept. of Chemistry, DSCE, Bangalore;Dr. Savitha M.B., Head, Dept. of Chemistry, SIT, Mangalore; Dr. Divakar, Head, Dept. ofChemistry, KSSEM, Bangalore; Dr. K. Jyothi Damodara, Head, Dept. of Chemistry,St. Joseph Engg. College, Mangalore; Dr. Manjunath, Associate Professor, Dept. ofChemistry, CMRIT, Bangalore; Dr. Sunil K., Associate Professor, Dept. of Chemistry, SSIT,

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Tumkur; Mr. Nagaraj, Associate Professor, Dept. of Chemistry, MVSCE, Mangalore; Mr.Saifulla Khan, Assistant Professor, Dept. of Chemistry, GCE, Bangalore; Dr. Sujata, Head,Dept. of Chemistry, VIT, Bangalore; Mr. Ganesh, Assistant Professor, Dept. of Chemistry,RGIT, Bangalore; Dr. Radha, Head, Dept. of Chemistry, T. John IT, Bangalore; Dr. Damodara,Head, Dept. of Chemistry, CCE, Mangalore; Dr. Vidyavathi A. Shastry, Head, Dept. ofChemistry, SEACE, Bangalore; Ms. Meena, Assistant Professor, SaIT, Bangalore and Mr.Mohana, Head, Dept. of Chemistry, GVIT, Kolar.

We also express sincere gratitude to all our teachers who inspired us to becomeauthors.

Authors

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VTU Syllabus(2015 Scheme)

MODULE 1: ELECTROCHEMISTRY AND BATTERY TECHNOLOGY

Electrochemistry: Introduction, Derivation of Nernst equation for electrode potential.Reference electrodes: Introduction, construction, working and applications of calomel andAg/AgCl electrodes. Measurement of electrode potential using calomel electrode. Ionselective electrode: Introduction, construction and working of glass electrode, determinationof pH using glass electrode. Concentration cells: Electrolyte concentration cells, numericalproblems.

Battery Technology: Introduction, classification – primary, secondary and reserve batteries.Characteristics – cell potential, current, capacity, electricity storage density, energy efficiency,cycle life and shelf life. Construction, working and applications of Zinc-Air, Nickel-metalhydride batteries. Lithium batteries: Introduction, construction, working and applications ofLi-MnO2 and Li-ion batteries.

Fuel Cells: Introduction, difference between conventional cell and fuel cell, limitations andadvantages. Construction, working and applications of methanol-oxygen fuel cell with H2SO4

electrolyte.

MODULE 2: CORROSION AND METAL FINISHING

Corrosion: Introduction, electrochemical theory of corrosion, galvanic series. Factorsaffecting the rate of corrosion: ratio of anodic to cathodic areas, nature of metal, nature ofcorrosion product, nature of medium – pH, conductivity, and temperature. Types of corrosion– Differential metal, differential aeration (pitting and water line) and stress. Corrosion control:Inorganic coatings – Anodizing of Al and phosphating; Metal coatings – Galvanization andTinning. Cathodic protection (sacrificial anodic and impressed current methods).

Metal Finishing: Introduction, Technological importance. Electroplating: Introduction,principles governing – polarization, decomposition potential and overvoltage. Factorsinfluencing the nature of electro deposit – current density, concentration of metal ion andelectrolyte; pH, temperature and throwing power of plating bath; additives – brighteners,levellers, structure modifiers and wetting agents. Electroplating of Nickel (Watt’s Bath) andChromium (decorative and hard). Electroless plating: Introduction, distinction betweenelectroplating and electroless plating, electroless plating of copper and manufacture ofdouble-sided Printed Circuit Board with copper.

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MODULE 3: FUELS AND SOLAR ENERGY

Fuels: Introduction, classification, calorific value – gross and net calorific values,determination of calorific value of fuel using bomb calorimeter, numerical problems. Cracking:Introduction, fluidized catalytic cracking, synthesis of petrol by Fishcher-Tropsch process,reformation of petrol, octane and cetane numbers. Gasoline and diesel knocking and theirmechanism, anti-knocking agents, power alcohol and biodiesel.

Solar Energy: Introduction, utilization and conversion, photovoltaic cells – construction andworking. Design of PV cells: modules, panels and arrays. Advantages and disadvantages ofPV cells. Production of solar grade silicon: Union carbide process, purification of silicon (zonerefining), doping of silicon-diffusion technique (n and p types).

MODULE 4: POLYMERS

Introduction, types of polymerization: Addition and condensation, mechanism ofpolymerization – free radical mechanism taking vinyl chloride as an example. Molecularweight of polymers: number average and weight average, numerical problems. Glasstransition temperature (Tg): Factors influencing Tg – Flexibility, inter-molecular forces,molecular mass, branching and cross linking and stereo regularity. Significance of Tg.Structure property relationship: crystallinity, tensile strength, elasticity and chemical resistivity.Synthesis, properties and applications of PMMA (plexi glass), Polyurethane andpolycarbonate. Elastomers: Introduction, synthesis, properties and applications of Siliconerubber. Adhesives: Introduction, synthesis, properties and applications of epoxy resin.Polymer Composites: Introduction, synthesis, properties and applications of Kevlar.Conducting polymers: Introduction, mechanism of conduction in Polyaniline and applicationsof conducting polyaniline.

MODULE 5: WATER TECHNOLOGY AND NANOMATERIALS

Water Technology: Introduction, boiler troubles with disadvantages and prevention methods– scale and sludge formation, priming and foaming, boiler corrosion (due to dissolved O2,CO2 and MgCl2). Determination of DO, BOD and COD, numerical problems on COD. Sewagetreatment: primary, secondary (activated sludge method) and tertiary methods. Softening ofwater by ion exchange process. Desalination of sea water by reverse osmosis and electrodialysis (ion selective).

Nanomaterials: Introduction, properties (size dependent). Synthesis – bottom-up approach(sol-gel, precipitation, gas condensation and chemical vapour condensation processes).Nanoscale materials – carbon nanotubes, nanowires, fullerenes, dendrimers, nanorods andnanocomposites.

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Contents

Preface (iii)

Acknowledgements (v) – (vi)

VTU Syllabus (2015 Scheme) (vii) – (viii)

1. Electrochemistry and Battery Technology 1 – 191.1 Electrochemistry 1

1.1.1 Introduction 11.1.2 Nernst Equation for Single Electrode Potential 31.1.3 Reference Electrodes 4

1.1.3.1 Calomel Electrode 41.1.3.2 Ag-AgCl Electrode 5

1.1.4 Measurement of Electrode Potential using Calomel Electrode 61.1.5 Electrolyte Concentration Cells 61.1.6 Ion Selective Electrode 8

1.1.6.1 Glass Electrode 81.1.7 Determination of pH using Glass Electrode 9

1.2 Battery Technology 101.2.1 Introduction 101.2.2 Classification of Batteries 111.2.3 Battery Characteristics 111.2.4 Nickel-Metalhydride (Ni-MH) Battery 121.2.5 Zinc-Air Battery 131.2.6 Li-MnO2 Battery 141.2.7 Li-ion Battery 15

1.3 Fuel Cells 161.3.1 Introduction to Fuel Cells 161.3.2 Advantages and Limitations of Fuel Cells 161.3.3 Difference between Conventional Cells and Fuel Cells 161.3.4 Methanol-oxygen Fuel Cell with H2SO4 as Electrolyte 16

1.4 Points to Remember 171.5 Review Questions from Recent VTU Papers 19

2. Corrosion and Metal Finishing 20 – 372.1 Corrosion 20

2.1.1 Introduction 202.1.2 Electrochemical Theory of Corrosion 212.1.3 Factors Affecting the Rate of Corrosion 21

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2.1.4 Galvanic Series 222.1.5 Types of Corrosion 222.1.6 Corrosion Control 24

2.1.6.1 Anodizing of Aluminium 252.1.6.2 Phosphating 252.1.6.3 Galvanizing (Anodic Metal Coating) 262.1.6.4 Tinning (Cathodic Metal Coating) 262.1.6.5 Cathodic Protection 27

2.2 Metal Finishing 282.2.1 Introduction 282.2.2 Technological Importance of Metal Finishing 282.2.3 Electroplating 28

2.2.3.1 Decomposition Potential 292.2.3.2 Overvoltage 292.2.3.3 Polarization 302.2.3.4 Factors Influencing the Nature of Electro Deposit 302.2.3.5 Electroplating of Nickel (Watt’s Bath) 322.2.3.6 Electroplating of Chromium (Decorative and Hard) 32

2.2.4 Electroless Plating 332.2.4.1 Distinction between Electroplating and Electroless

Plating 332.2.4.2 Electroless Plating of Copper for PCB Manufacture 33


3. Fuels and Solar Energy 38 – 523.1 Fuels 38

3.1.1 Introduction 383.1.2 Classification 383.1.3 Calorific Value – Gross and Net Calorific Values 383.1.4 Determination of Calorific Value of Fuel using Bomb Calorimeter 393.1.5 Numerical Problems 403.1.6 Various Constituents of Petroleum 413.1.7 Cracking 413.1.8 Synthesis of Petrol by Fischer-Tropsch Process 423.1.9 Octane Number 43

3.1.10 Reformation of Petrol 433.1.11 Mechanism of Gasoline Knocking 443.1.12 Anti-knocking Agents 453.1.13 Cetane Number 453.1.14 Mechanism of Knocking in Diesel Engine 45

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3.1.15 Power Alcohol 463.1.16 Biodiesel 46

3.2 Solar Energy 473.2.1 Introduction 473.2.2 Utilization and Conversion of Solar Energy 473.2.3 Photovoltaic Cells 473.2.4 Design of PV Cells: Modules, Panels and Arrays 483.2.5 Advantages and Disadvantages of PV Cells 493.2.6 Production of Metallurgical Grade Silicon 493.2.7 Production of Solar Grade Silicon by Union Carbide Process 493.2.8 Purification of Silicon by Zone Refining 503.2.9 Doping of Silicon by Diffusion Technique (n and p Types) 50


4. Polymers 53 – 664.1 Introduction 534.2 Types of Polymerization 53

4.2.1 Addition Polymerization 534.2.2 Condensation Polymerization 54

4.3 Mechanism of Free Radical Polymerization 544.4 Molecular Weight of Polymers 554.5 Glass Transition Temperature (Tg) 574.6 Structure-Property Relationship 584.7 Polymethylmethacrylate (PMMA) or Plexiglass 594.8 Polyurethane (PU) 604.9 Polycarbonate (PC) 604.10 Elastomers 61

4.10.1 Silicone Rubber 614.11 Adhesives 61

4.11.1 Epoxy Resin 624.12 Polymer Composites 62

4.12.1 Kevlar Fibre 624.13 Conducting Polymers 63

4.13.1 Mechanism of Conduction in Polyaniline 644.14 Points to Remember 654.15 Review Questions from Recent VTU Papers 66

5. Water Technology and Nanomaterials 67 – 865.1 Water Technology 67

5.1.1 Introduction 67

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5.1.2 Boiler Troubles 675.1.2.1 Scale and Sludge 685.1.2.2 Priming and Foaming 68

5.1.3 Boiler Corrosion 685.1.4 Determination of Dissolved Oxygen (DO) in Water Samples

(Winkler’s Method) 695.1.5 Determination of Chemical Oxygen Demand (COD) of Water

Samples 695.1.6 Determination of Biological Oxygen Demand (BOD) of Water

Samples 705.1.7 Numerical Problems on COD 705.1.8 Sewage Treatment 715.1.9 Softening of Water by Ion Exchange Method 72

5.1.10 Desalination of Sea Water 735.1.10.1 Reverse Osmosis 745.1.10.2 Electrodialysis 74

5.2 Nanomaterials 755.2.1 Introduction 755.2.2 Size Dependent Properties of Nanomaterials 755.2.3 Bottom-up Approach for the Synthesis of Nanomaterials 77

5.2.3.1 Sol-gel Method 775.2.3.2 Precipitation Method 775.2.3.3 Gas Condensation Method 785.2.3.4 Chemical Vapour Condensation Process 78

5.2.4 Nanoscale Materials 795.2.4.1 Carbon Nanotubes 795.2.4.2 Nanowires and Nanorods 805.2.4.3 Fullerenes 815.2.4.4 Dendrimers 825.2.4.5 Nanocomposites 83


Latest Development on Relevant Topics 87 – 88Index 89 – 91

1

Module 1

Electrochemistry and BatteryTechnology

Module Objectives: It is essential to understand existing energy technologies and next generation solutions, to

become successful engineers. This module is designed to give the fundamental concepts ofelectrochemistry, construction, working and applications of batteries and fuel cells that findwide applications in automobiles and electronic gadgets.

The students also understand the role of electrodes in qualitative and quantitativemeasurement of analytes.

1.1 ELECTROCHEMISTRY1.1.1 Introduction

Electrochemistry is the study of chemical processes that cause electrons to move. This movementof electrons is called electricity, which is generated by movement of electrons from one electrode toanother in a reaction known as an oxidation-reduction (redox) reaction.

Oxidation is the lose of electrons whereas reduction refers to the gain of electrons. (OIL RIG:Oxidation Is Lose of electrons; Reduction Is Gain of electrons).

Oxidation takes place at anode whereas reduction takes place at cathode. (An Ox Red Cat:Anode Oxidation; Reduction Cathode).

Electrochemical cells are broadly divided into two types;1. Galvanic cells2. Electrolytic cellsA galvanic cell is a device where chemical energy is spontaneously converted to electrical energy.

Example: discharging of a battery.Electrolytic cell is a device where electrical energy is applied to drive a non spontaneous

chemical reaction. Example: charging of a battery, and electroplating processes.

Engineering Chemistry2

Construction and Working of Galvanic CellIt consists of two dissimilar electrodes dipped in their respective electrolyte solutions which are

connected internally by means of salt bridge or porous membrane. A voltmeter may be used tomeasure the cell potential. The salt bridge maintains ionic balance while preventing the mixing ofanodic and cathodic solutions (see Figure 1.1).

Figure 1.1: Galvanic Cell

Example for galvanic cell is Daniel cell:Zn | ZnSO4(1M) || CuSO4(1M) | Cui.e., Anode | Anode solution || Cathode solution | Cathodewhere single line is used to indicate different phases and double line to indicate salt bridge.

Electrochemistry and Battery Technology 3

At anode: Zinc electrode undergoes oxidationZn Zn2+ + 2e−

At cathode: Copper ions undergo reductionCu2+ + 2e− Cu

Net cell reaction is obtained by adding anode and cathode reactions as given below:Zn + Cu2+ Zn2+ + Cu

Electromotive force (EMF) of the cell at standard conditions or cellE is calculated using the

equation:cellE =

anodecathode E– E

where E° is standard electrode potential measured at standard conditions, i.e., 298K, 1Mconcentration and 1 atm.

Electrode E° (in volts)Zn2+/Zn –0.76Fe2+/Fe –0.44Cu2+/Cu 0.34Ag+/Ag 0.80

In a galvanic cell, the electrode with lower E° value act as anode and the electrode with higher E°value act as cathode. For example, in a Daniel cell, Zn electrode (E° = –0.76V) acts as anode, whereasthe Cu electrode (E° = 0.34V) acts as cathode.

1.1.2 Nernst Equation for Single Electrode PotentialNernst equation relates single electrode potential (E) with nature of the metal, concentration of

metal ions and temperature. Consider a reversible redox reactionMn+ + ne– M

A thermodynamic relationship known as Van’t Hoff’s isotherm equation represented below, canbe applied to the above equilibrium to derive Nernst equation,

∆G = ∆G° + RT ln Kc ... (1.1)Decrease in free energy is related to maximum work done,

−∆G = Wmax = nFE ... (1.2)−∆G° = nFE° ... (1.3)

Kc =][M

[M] [reactant][product]

n ... (1.4)

Substitute equations 1.2, 1.3 and 1.4 in 1.1,

−nFE = −nFE° + RT ln][M

[M]n


Divide by –nF; substitute ln = 2.303 log andsubstitute [M] = 1 (since concentration of pure metal is taken as unity)

E = E° − 2.303][M

1log nFRT

n

By rearranging the above equation, the Nernst equation for single electrode potential is obtained;

E = E° +nF

RT 2.303 log [Mn+]

or

E = E° +n

0.0591 log [Mn+] at 298K

Nernst equation clearly indicates that the potential of a single electrode varies with concentrationof metal ions in the solution. Single electrode potential is determined by using a reference electrode.

1.1.3 Reference ElectrodesReference electrodes are electrodes of fixed potential with which potential of other electrodes can

be determined. There are two types of reference electrodes; Primary reference electrode [Example: Standard Hydrogen Electrode (SHE), E° = 0]. Due to

difficulty in handling hydrogen gas, secondary reference electrodes are preferred. Secondary reference electrode (Examples: Calomel electrode and Ag-AgCl electrode).

Construction, working and applications of secondary reference electrodes are discussed in thefollowing section.

1.1.3.1 Calomel Electrode

Construction:Calomel electrode is constructed by filling a

paste of Hg and Hg2Cl2 at the bottom of a narrowglass tube having a porous plug at the bottom end.Liquid mercury is then filled above the paste. Tomeasure the potential of the electrode a platinumwire is dipped in liquid mercury. This narrowglass tube is placed inside an outer glass tubefilled with KCl solution. The porous plug at thebottom of outer tube acts as salt bridge.

The electrode can be represented as:Hg(l) | Hg2Cl2(s) | KCl(aq)

Working:The net reversible electrode reaction is;

Hg2Cl2 + 2e− 2Hg + 2Cl–Figure 1.2: Calomel Electrode


Nernst equation for calomel electrode is found to be;E = E° − 0.0591 log[Cl–] at 298K

Its electrode potential is decided by the concentration of chloride ions and the electrode isreversible with respect to chloride ions.

Concentration of KCl E (in volts)Saturated (4M) 0.242

1M 0.2800.1M 0.334

Applications: It is used as a secondary reference electrode in the measurement of single electrode potentials. It is used in potentiometric quantitative analysis.

1.1.3.2 Ag-AgCl Electrode

Construction:It consists of a Ag wire coated with its

sparingly soluble salt AgCl, and is immersed in asolution containing Cl– ions. Porous plug at thebottom of the glass tube acts as salt bridge.

The electrode can be represented as:Ag(s) | AgCl(s) | KCl(aq)

Working:The net reversible electrode reaction is;

AgCl + e– Ag + Cl–

Nernst equation for Ag-AgCl electrode isfound to be;

E = E° − 0.0591 log[Cl–] at 298KIts electrode potential is decided by the concentration of chloride ions and the electrode is

reversible with respect to chloride ions.Concentration of KCl E (in volts)

Saturated (4M) 0.1991M 0.222

0.1M 0.291

Applications: It is used as a secondary reference electrode in the measurement of single electrode potentials. It is used as internal reference electrode in glass electrode.

Figure 1.3: Ag-AgCl Electrode


1.1.4 Measurement of Electrode Potential usingCalomel Electrode

Potential of any electrode can be measured by combiningwith a calomel reference electrode. For example, the followingcell is constructed to measure the potential of Zn electrode.

Cell representation:Zn | Zn2+ || KCl | Hg2Cl2 | Hg

cellE =

anodecathode E– E

cellE =

ZnSCE E– E

ZnE =

cellSCE E– E

cellE is read from the voltmeter as 1.0V,

ZnE = 0.2422V − 1.0V

ZnE = −0.76V

1.1.5 Electrolyte Concentration CellsElectrolyte concentration cell is a type of

galvanic cell that generates electricity when twoelectrodes of same metal are in contact with solutionsof its ions of different concentration. Potentialdifference arises due to difference in electrolyteconcentrations.

Example of concentration cell:

Cu | Cu || Cu|Cu M1.0 C2

0.001M C2

21

Metal immersed in dilute solution act as anode(C1 = 0.001M) whereas the metal immersed inconcentrated solution act as cathode (C2 = 0.1M).

Cell reactions:

At anode: Cu

20.001M C1Cu + 2e–

At cathode:

20.1M C2Cu + 2e– Cu

Derivation of an Expression for EMF of Concentration CellConsider the concentration cell shown in the figure. Its EMF is given by,

Ecell = Ecathode − Eanode

Nernst equation for anode:

Eanode =nF

2.303RT Eanode log C1

Figure 1.4: Measurement ofelectrode potential using calomel

electrode

Figure 1.5: Concentration Cell


Nernst equation for cathode:

Ecathode =nF

2.303RT Ecathode log C2

Substitute Nernst equation for anode and cathode in Ecell equation:

Ecell =nF

2.303RT )E– (E anodecathode log1

2

CC

In concentration cell, anode and cathode electrodes are same, henceanodecathode E– E = 0

Therefore the Nernst equation for concentration cell can be written as;

Ecell =nF

2.303RT log1

2

CC

or

Ecell =n

0.0591 log1

2

CC at 298K

Numerical ProblemEMF of the cell Cu | CuSO4 (0.001M) || CuSO4 (X) | Cu is 0.0595V at 25°C. Find X value.It is clear that C1 = 0.001M, C2 = X and n = 2;Apply Nernst equation for concentration cell

Ecell =n

0.0591 log1

2

CC at 298K

0.0591n Ecell = log

1CX

Antilog

0.0591n Ecell =

1CX

0.001 × Antilog

0.05912 0.0595 = X

0.001 × 103 = XX = 0.103M


1.1.6 Ion Selective Electrode

Introduction Ion selective electrode is very selective towards particular type of ions and develop a potential

proportional to the concentration of that ions. The sensitive part of the electrode is its membrane which allows the exchange of selective

ions at the interface.There are generally three types of ion selective membranes.1. Glass membrane: It is selective to H+ ions and hence is used in pH measurements. It is a

three dimensional network of silicate with Na+ ions. H+ ions in solution is selectivelyexchanged with Na+ ions of the silicate network.

2. Solid state membrane: LaF3 doped EuF2 crystal is used for the detection of fluoride ions.3. Liquid membrane on porous polymer: Polymer membrane containing large organic

molecules capable of interacting with particular ions.

1.1.6.1 Glass Electrode

Construction:Glass electrode is constructed by immersing Ag-AgCl internal

reference electrode in a glass bulb containing 0.1M HCl solution.The glass bulb is made up of a long glass tube with a thin highlyconducting glass membrane at the bottom. The glass membrane isselective to H+ ions in the solution, and is made up of silicate glasshaving composition of 72% SiO2, 22% Na2O and 6% CaO.

The electrode can be represented as;Ag | AgCl | 0.1M HCl | Glass membrane

Working:When a glass bulb containing 0.1M HCl solution is immersed in

an acidic solution of different concentration, a boundary potential (Eb)is developed across the gel layers of the glass membrane.Figure 1.6: Glass Electrode

Ag/AgCl


This boundary potential (Eb) arises due to the difference in concentration of H+ ions inside andoutside of the glass bulb.

Eb = 0.0591 log1

2

CC

C1 = Concentration of H+ inside the bulb, is a constant; C2 = Concentration of H+ ouside the bulb.Eb = 0.0591 log [C2] − 0.0591 log [C1]

Substitute –0.0591 log [C1] = K, a constantThen the equation becomes:

Eb = K + 0.0591 log [C2] = K + 0.0591 log [H+]Substitute log [H+] = –pHThe final equation for Eb is obtained as,

Eb = K − 0.0591 pHThe potential of glass electrode (EG) includes contribution from 3 factors,1. Boundary potential (Eb)2. Potential of Ag-AgCl reference electrode dipped inside the bulb, EAg/AgCl

3. Assymetric potential due to slight inhomogeneity of the inner and outer surfaces of the glassmembrane, EAsy

EG = Eb + EAg/AgCl + EAsy

Substitute Eb value;EG = K − 0.0591pH + EAg/AgCl + EAsy

EG = L − 0.0591pH

where constant, L = K + EAg/AgCl + EAsy

1.1.7 Determination of pH using Glass ElectrodeTo measure pH of an unknown solution, a glass electrode is coupled with calomel electrode and

connected to a potentiometer (or pH meter for reading pH directly), see Figure 1.7.The cell formed is represented as,Hg | Hg2Cl2 | KCl || Solution of unknown pH | Glass electrodeThe potential established at the glass electrode is higher than that of the calomel electrode, hence

glass electrode is taken as cathode.


Figure 1.7: Determination of pH


Ecell = EG − ESCE

Substituting for EG value,Ecell = [L − 0.0591pH] − ESCE

The above equation is rearranged to obtain the expression for pH,

pH =0.0591

E– E– L cellSCE

1.2 BATTERY TECHNOLOGY1.2.1 Introduction

Battery is a device consisting of one or more galvanic cells connected in series or parallel orboth. It converts chemical energy into electricity through redox reactions.

Basic Components of Battery Anode (–ve): It undergoes oxidation and release electrons to the external circuit. Cathode (+ve): Active species at cathode undergoes reduction by accepting electrons from

external circuit. Electrolyte: It is a solution of salt or alkali or acid. It allows the movement of ions inside the

cell between anode and cathode. Example: NaCl, KOH, H2SO4, etc. Separator: It separates anode and cathode to prevent internal short circuiting, but allows

transport of ions between anode and cathode and maintain electrical neutrality. Example:cellulose, nafion membranes, etc.

Cathode current collector, anode current collector, rubber seal and container are the minorcomponents of battery.

Solution ofunknown pH


1.2.2 Classification of Batteries Primary battery: This battery cannot be recharged, because cell reaction is irreversible.

Example: Zn-MnO2 battery, Li-MnO2 battery. Secondary battery: This battery can be recharged by passing electric current, because cell

reactions are reversible. Example: Lead acid battery, Ni-MH battery. Reserve battery: In this battery, one of the component is stored separately, and is

incorporated into battery when required. Example: Mg-AgCl and Mg-CuCl battery. They areactivated by adding sea water. These batteries have high reliability and long shelf life, hencethey find applications in missiles and submarines.

1.2.3 Battery Characteristics Cell potential: Cell potential (or voltage) is the electrical force that drive electric current

between electrodes. Voltage of a cell is given by the equation;Ecell = (EC − EA) − ηA − ηC − iRcell

where, ηA and ηC are overpotential at anode and cathode respectively. Overpotentials shouldbe less to derive maximum voltage. Rcell is internal resistance of the cell. Internal resistanceshould also be less to derive maximum voltage.

Current: “Current is the rate at which electric charge flows in a circuit and is expressed inAmpere”. High current can flow if there is rapid electron transfer reaction.

Capacity: “It is the charge in Ampere-hours (Ah) that can be withdrawn from fully chargedcell or battery under specified conditions”. It is determined by Faraday’s relation:

C =M

WnF

(where, W = weight of active material; F = Faraday’s constant; M = Molar mass of activematerial; n = number of electrons involved in cell reaction).

Electricity storage density: “It is the measure of charge per unit mass stored in the battery(Ah/Kg)”. The mass of the battery includes electrolyte, electrodes, terminals, case, etc.Lighter elements lead to higher electricity storage density. For example, Li anode lead tohigher electricity storage density when compared with the same amount of Zn.

Energy Efficiency: Energy efficiency for a secondary battery is given by:

Energy efficiency =charge torequiredEnergy

dischargeon releasedEnergy × 100

Cycle life: “The number of charge/discharge cycles that are possible before failure occurs inthe case of secondary batteries is called as cycle life”. The cycle life of a battery is affected bycorrosion in contacts and shedding of active materials from electrodes.

Shelf life: It is essential for most batteries to be stored, sometimes for many years, withoutself discharge or corrosion of electrodes. Shelf life is defined as “duration of storage underspecific conditions without any loss in performance”.


1.2.4 Nickel-Metalhydride (Ni-MH) BatteryConstruction:

Figure 1.8: Ni-MH Battery

In Ni-MH batterries, a highly porous nickel substrate pasted with NiO(OH) function as cathode.A highly porous nickel grid pasted with metal hydrides (VH2, ZrH2) and hydrogen storage alloy(LaNi5) function as anode. Polypropylene is used as separator and an aqueous solution of KOH servesas electrolyte.

Cell representation: MH | KOH(5.35M) | Ni(OH)2, NiO(OH)

Working:

Anode reaction: MH + OH– discharging

charging M + H2O + e–

Cathode reaction: NiOOH + H2O + e– discharging

charging Ni(OH)2 + OH–

Overall reaction: MH + NiOOH discharging

charging M + Ni(OH)2

Applications: These are high energy density batteries used in phones, cameras and electric vehicles.


1.2.5 Zinc-Air BatteryConstruction:

Figure 1.9: Zn-Air battery

In a zinc-air battery, anode reactant is granulated powder of zinc mixed with electrolyte KOH.The cathode reactant is oxygen which diffuse into porous carbon cathode through a layer of gas (air)permeable membrane.

Cell representation: Zn | KOH(6M) | Air,C

Working:

Anode reaction: 2Zn + 4OH– discharging

charging 2ZnO + 2H2O + 4e–

Cathode reaction: O2 + 2H2O + 4e– discharging

charging 4OH–

Overall reaction: 2Zn + O2discharging

charging 2ZnO

Applications: These high energy density batteries are used in hearing aids, medical devices, etc.

Zinc powder/KOH(Anode)


1.2.6 Li-MnO2 batteryConstruction:

Figure 1.10: Li-MnO2 Battery

In Li-MnO2 battery, lithium metal is used as anode and heat treated MnO2 is used as cathode.Lithium salt (LiCl or LiClO4) in mixed organic solvent (propylene carbonate and 1-2-dimethoxyethane)is used as electrolyte. Non-woven polypropylene is used as separator.

Cell representation: Li|LiCl in organic solvent|Mn(IV)O2|Mn(III)O2Li+

Working:During cell reaction, lithium metal loses an electron to form lithium ions. The electron reduces

cathode active material Mn(IV) as Li+ enters into crystal lattice.

Anode reaction: Li ingargdisch Li+ + e–

Cathode reaction: Mn(IV)O2 + Li+ + e– ingargdisch Mn(III)O2Li+

Overall reaction: Li + Mn(IV)O2 ingargdisch Mn(III)O2Li+

Applications: These high energy density primary batteries are used in electronic watches, toys, etc.


1.2.7 Li-ion batteryConstruction:

Figure 1.11: Li-ion Battery

In Li-ion battery, the anode is made up of layered graphite intercalated with lithium atoms. Thecathode is a lithium metal oxide such as LiCoO2. Lithium salt (LiPF6) in mixed organic solvent(ethylene carbonate-dimethyl carbonate) is used as electrolyte and non-woven polypropylene is usedas separator.

Cell representation: Li|Li+, C|LiPF6 in ethylene carbonate|LiCoO2

Working:During cell discharge, lithium atoms present in between graphite layers lose electrons to form

lithium ions. The electrons flow through external circuit to cathode and lithium ions flow throughelectrolyte to cathode. At cathode, Co4+ is reduced to Co3+ and lithium ions are inserted into thelayered structure of metal oxide.

Anode reaction: LixCdischarging

charging xLi+ + xe– + C

Cathode reaction: Li1 – xCoO2 + xLi+ + xe– discharging

charging LiCoO2

Overall reaction: LixC + Li1 – xCoO2discharging

charging LiCoO2 + C

During charging, Co3+ is oxidized to Co4+ liberating lithium ions and electrons. The electronsflow through external circuit to anode and lithium ions flow through the electrolyte to anode. At anode,lithium ions are reduced to lithium atom and inserted back into layered structure of graphite.

Applications: These high energy density secondary batteries are used in electronic devices such as mobile

phones, laptops, electric vehicles, and also in defence and aerospace applications.


1.3 FUEL CELLS1.3.1 Introduction to Fuel Cells

Fuel cell is “a galvanic cell that converts the chemical energy of a fuel (hydrogen, methanol, etc.,)and an oxidant into electricity”.

Fuel cell has two electrodes (anode and cathode) and electrolyte, similar to a battery. Howeverthe major difference is reactants (fuel and oxidant) are continuously supplied and products arecontinuously removed, whereas in a battery reactants are stored inside and the products are notremoved.

Fuel cell is represented as; Fuel | anode | electrolyte | cathode | oxidant.

1.3.2 Advantages and Limitations of Fuel CellsAdvantages

High power efficiency and can produce direct current for long time. Eco-friendly as the products of overall reaction is not toxic.

Limitations Fuel cells produce electricity only until fuel and oxidants are supplied. Fuels in the form of gases (such as H2) need to be stored in tanks at high pressure. It requires expensive catalysts.

1.3.3 Difference between Conventional Cells and Fuel CellsS.No. Conventional cells (batteries) Fuel cells

1 Reactants are stored inside the cell Reactants are supplied from outside2 Reaction products are toxic Eco-friendly3 Secondary cells can be charged It cannot be charged4 Expensive catalysts not required Expensive catalysts required

1.3.4 Methanol-oxygen Fuel Cell with H2SO4 as ElectrolyteConstruction:

In this type of fuel cell, methanol is used as fuel and oxygen is used as oxidant. The anode andcathode are porous nickel sheets coated with electrocatalysts. Pt/Ru catalyst on anode and Pt alone oncathode. Methanol mixed with sulphuric acid is passed through anode chamber. Pure oxygen is passedthrough cathode chamber. Electrolyte sulphuric acid is placed in the central chamber. To prevent thediffusion of anode reactant methanol into cathode chamber, a proton conducting membrane is placednear cathode. The membrane allows only protons to cathode.


Figure 1.12: Methanol-oxygen Fuel Cell

Working:Anode reaction: CH3OH + H2O CO2 + 6H+ + 6e–

Cathode reaction: 121 O2 + 6H+ + 6e– 3H2O

Overall reaction: CH3OH + 121 O2 CO2 + H2O

Applications: It is used in military applications and in large scale power productions. It is also used in fuel cell vehicles and space shuttles.

1.4 POINTS TO REMEMBER Single electrode potential (E) is a potential developed when a metal (electrode) is dipped in a

solution of its own ions. Standard electrode potential (E°) is an electrode potential measured at standard conditions

(i.e., 298K, 1M concentration and 1 atm). Galvanic cell is a cell where chemical energy is spontaneously converted to electric energy. Electrolytic cell is a cell where electric energy is applied to drive a non spontaneous chemical

reaction. EMF or Ecell is the potential difference between cathode and anode,


Nernst equation relates electrode potential with concentration of metal ions. Reference electrodes are electrodes of fixed potential with which potential of other electrodes

can be determined. Examples: SHE, calomel electrode and Ag-AgCl electrode.


The electrode potential of calomel and Ag-AgCl reference electrodes are decided by theconcentration of chloride ions and are reversible with respect to chloride ions.

Concentration cell is a type of galvanic cell that generates electricity when two electrodes ofsame metal are in contact with solution of its ions of different concentration.

Ion selective electrode is very selective towards a particular type of ion and develop apotential proportional to the concentration of that ions. Example: glass electrode is an ionselective electrode selective to H+ ions and is used in pH measurements.

Glass electrode is constructed by immersing Ag-AgCl internal reference electrode in glassbulb containing 0.1M HCl. The glass bulb is made of a glass membrane which is selective toH+ ions.

pH of a solution is determined by coupling glass electrode with calomel electrode. Battery is a device consisting of one or more cells connected in series or parallel or both. Capacity of a battery is defined as the charge in ampere-hours (Ah) that can be withdrawn

from fully charged battery under specified conditions,

C =M

WnF

Table 1.1: Summary of Construction and Working of Various Batteries and Fuel CellBattery

componentsand

reactions

Ni-MH battery Zn-Air battery Li-MnO2 battery Li-ion battery Methanol-O2

Fuel Cell

Anode Ni grid coatedwith MH and H2

storage alloyLaNi5

Zn powder Li metal Li atomsintercalated inlayered graphite

Ni sheet coatedwith Pt

Cathode Ni grid coatedwith NiO(OH)

Porous carbon MnO2 LiCoO2 Ni sheet coatingwith Pt/Ru

Electrolyte KOH solution KOH (6M) LiCl in organicsolvent(propylenecarbonate + 1,2-dimethoxyethane)

LiPF6 in mixedorganic solvent(ethylenecarbonate anddimethylcarbonate

H2SO4

Anodereaction

MH + OHdis

char M +

H2O + e

2Zn + 4OH–

dis

ch arg2ZnO + 2H2O +4e–

Li dis Li+ +e–

LixC dis

char

XLi+ + xe– + C

CH3OH + 6H2O CO2 + 6H+ +6e–

CathodeReaction

NiOOH + H2O +e– dis

char

Ni(OH)2 + OH–

O2 + 2H2O +4e– dis

char

4OH–

Mn(IV)O2 + Li+ +e– dis

Mn(III)O2Li+

Li1 – x CoO2 +XLi+ + xe–

dis

char LiCoO2

121 O2 + 6H+ +

6e– 3H2O

OverallReaction

MH + NiOOHd

c M +

Ni(OH)2

2Zn + O2dis

ch arg2ZnO

Li + Mn(IV)O2

gdischargin

Mn(III)O2Li+

LixC + Li1 – X

CoO2dis

char

LiCoO2 + C

CH3OH +1

21 O2 CO2 +

H2O


1.5 REVIEW QUESTIONS FROM RECENT VTU PAPERS1. Derive Nernst equation for single electrode potential. [Jun. 2016, Dec. 2015, Dec. 2014]2. Define reference electrode. Discuss the construction and working of calomel electrode.

[Dec. 2015, Jun. 2015, Dec. 2014]3. Explain the construction and working of silver-silver chloride electrode. [Jun. 2016]4. What are concentration cells? Derive an expression for EMF of a concentration cell.5. The emf of the cell Cu | CuSO4 (0.001M) || CuSO4 (XM) | Cu is 0.0595V at 25°C. Find the value of

X. [Dec. 2015]6. What are concentration cells. The emf of the cell Ag | AgNO3 (0.0083M) || AgNO3 (XM) | Ag was

found to be 0.074V at 298K. Calculate the value of X and write cell reactions. [Dec. 2014]7. A cell is obtained by combining two Cd electrodes immersed in cadmium sulphate solutions

of 0.1M and 0.5M at 25°C. Give the cell representation, cell reactions and calculate EMF ofthe cell. [Jun. 2015]

8. What are ion selective electrodes. Discuss the construction and working of glass electrode.[Jun. 2016, Jun. 2015]

9. What are batteries. Explain the following battery characteristics.(a) Cell potential [Dec. 2015](b) Current(c) Capacity [Dec. 2015, Dec. 2014](d) Energy efficiency [Jun. 2016](e) Shelf life [Jun. 2016, Dec. 2015](f) Electricity storage density(g) Cycle life [Jun. 2016, Dec. 2014]

10. Describe the construction and working of Zn-Air battery. [Jun. 2016, Jun. 2015]11. Describe the construction and working of Ni-MH battery. Mention its applications.

[Jun. 2016, Dec. 2014]12. Discuss the construction and working of Li-MnO2 battery. [Jun. 2015]13. Describe the construction and working of Li-ion battery. [Dec. 2014]14. What is fuel cell. Mention its advantages. Distinguish between conventional cell and fuel cell.

[Jun. 2015, Dec. 2015]15. Discuss the construction and working of methanol-oxygen fuel cell. [Jun. 2016, Jun. 2015,

Dec. 2014]

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