ENGINEERING CHEMISTRY (For VTU Choice Based Credit System Syllabus 2015)

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2 A Concise Textbook on ENGINEERING CHEMISTRY (For VTU Choice Based Credit System Syllabus 2015) Dr. C. Muthukumar Professor and Head, Dept. of Chemistry, M.V.J. College of Engineering, Bangalore. Dr. Siju N. Antony Associate 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 (i)

3 Authors No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording and/or otherwise without the prior written permission of the publisher. First Edition : 2016 Published by : Mrs. Meena Pandey for Himalaya Publishing House Pvt. Ltd., Ramdoot, Dr. Bhalerao Marg, Girgaon, Mumbai Phone: / , Fax: himpub@vsnl.com; Website: Branch Offices : New Delhi : Pooja Apartments, 4-B, Murari Lal Street, Ansari Road, Darya Ganj, New Delhi Phone: / ; Fax: Nagpur : Kundanlal Chandak Industrial Estate, Ghat Road, Nagpur Phone: / ; Telefax: Bengaluru : Plot No , 2nd Main Road Seshadripuram, Behind Nataraja Theatre, Bengaluru Phone: ; Mobile: / Hyderabad : No , Lingampally, Besides Raghavendra Swamy Matham, Kachiguda, Hyderabad Phone: / Chennai : New-20, Old-59, Thirumalai Pillai Road, T. Nagar, Chennai Mobile: Pune : First Floor, Laksha Apartment, No. 527, Mehunpura, Shaniwarpeth (Near Prabhat Theatre), Pune Phone: / ; Mobile: Lucknow : House No. 731, Shekhupura Colony, Near B.D. Convent School, Aliganj, Lucknow Phone: ; Mobile: Ahmedabad : 114, SHAIL, 1st Floor, Opp. Madhu Sudan House, C.G. Road, Navrang Pura, Ahmedabad Phone: ; Mobile: Ernakulam : 39/176 (New No. 60/251), 1st Floor, Karikkamuri Road, Ernakulam, Kochi Phone: / ; Mobile: Bhubaneswar : 5 Station Square, Bhubaneswar (Odisha). Phone: ; Mobile: Kolkata : 108/4, Beliaghata Main Road, Near ID Hospital, Opp. SBI Bank, Kolkata Phone: ; Mobile: DTP by : Priyanka M. Printed at : M/s Sri Sai Art Printer Hyderabad. On behalf of HPH. (ii)

4 Preface Engineering has stretched into different frontiers of our lives promising ever increasing bundles of opportunities and challenges. Engineering Chemistry plays an inevitable role in providing a fundamental as well as broad knowledge of theoretical, applied and experimental chemistry to the budding engineers to enable them to embark on professional careers of their choice. It gives us immense pleasure in bringing forward this book entitled A Concise Textbook on Engineering Chemistry which comprises of five modules as per the latest Visvesvaraya Technological University (VTU) Choice Based Credit System (CBCS) Syllabus This book is intended to cater to the needs and aspirations of both I st and II nd 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 of learning. We highly appreciate constructive comments and suggestions for improvement. Authors (iii)

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6 Acknowledgements It is by the love and blessings of the Almighty that we are able to complete this book successfully 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 the necessary facilities. The authors have a great pleasure in thanking the publisher, Himalaya Publishing House Pvt. Ltd., Mumbai for inviting the authors to write this concise textbook on Engineering Chemistry. Writing a technical book needs deep knowledge and intuition into the subject along with references 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 in accomplishing 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. Srabani Ghosh, Associate Professor, Dept. of Chemistry, MVJCE, Bangalore; Dr. T.M. Veeresh, Associate Professor, Dept. of Chemistry, PDIT, Hospet; Dr. R.K. Patil, Head, Dept. of Chemistry, 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., Assistant Professor, 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. of Chemistry, KSSEM, Bangalore; Dr. K. Jyothi Damodara, Head, Dept. of Chemistry, St. Joseph Engg. College, Mangalore; Dr. Manjunath, Associate Professor, Dept. of Chemistry, CMRIT, Bangalore; Dr. Sunil K., Associate Professor, Dept. of Chemistry, SSIT, (v)

7 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. of Chemistry, 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 become authors. Authors (vi)

8 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 and Ag/AgCl electrodes. Measurement of electrode potential using calomel electrode. Ion selective electrode: Introduction, construction and working of glass electrode, determination of ph using glass electrode. Concentration cells: Electrolyte concentration cells, numerical problems. 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-metal hydride batteries. Lithium batteries: Introduction, construction, working and applications of Li-MnO2 and Li-ion batteries. Fuel Cells: Introduction, difference between conventional cell and fuel cell, limitations and advantages. 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. Factors affecting the rate of corrosion: ratio of anodic to cathodic areas, nature of metal, nature of corrosion 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 and Tinning. Cathodic protection (sacrificial anodic and impressed current methods). Metal Finishing: Introduction, Technological importance. Electroplating: Introduction, principles governing polarization, decomposition potential and overvoltage. Factors influencing the nature of electro deposit current density, concentration of metal ion and electrolyte; ph, temperature and throwing power of plating bath; additives brighteners, levellers, structure modifiers and wetting agents. Electroplating of Nickel (Watt s Bath) and Chromium (decorative and hard). Electroless plating: Introduction, distinction between electroplating and electroless plating, electroless plating of copper and manufacture of double-sided Printed Circuit Board with copper. (vii)

9 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 their mechanism, anti-knocking agents, power alcohol and biodiesel. Solar Energy: Introduction, utilization and conversion, photovoltaic cells construction and working. Design of PV cells: modules, panels and arrays. Advantages and disadvantages of PV cells. Production of solar grade silicon: Union carbide process, purification of silicon (zone refining), doping of silicon-diffusion technique (n and p types). MODULE 4: POLYMERS Introduction, types of polymerization: Addition and condensation, mechanism of polymerization free radical mechanism taking vinyl chloride as an example. Molecular weight of polymers: number average and weight average, numerical problems. Glass transition temperature (Tg): Factors influencing Tg Flexibility, inter-molecular forces, molecular mass, branching and cross linking and stereo regularity. Significance of T g. Structure property relationship: crystallinity, tensile strength, elasticity and chemical resistivity. Synthesis, properties and applications of PMMA (plexi glass), Polyurethane and polycarbonate. Elastomers: Introduction, synthesis, properties and applications of Silicone rubber. 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 applications of 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, CO 2 and MgCl 2). Determination of DO, BOD and COD, numerical problems on COD. Sewage treatment: primary, secondary (activated sludge method) and tertiary methods. Softening of water by ion exchange process. Desalination of sea water by reverse osmosis and electro dialysis (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 and nanocomposites. (viii)

10 Contents Preface Acknowledgements VTU Syllabus (2015 Scheme) (iii) (v) (vi) (vii) (viii) 1. Electrochemistry and Battery Technology Electrochemistry Introduction Nernst Equation for Single Electrode Potential Reference Electrodes Calomel Electrode Ag-AgCl Electrode Measurement of Electrode Potential using Calomel Electrode Electrolyte Concentration Cells Ion Selective Electrode Glass Electrode Determination of ph using Glass Electrode Battery Technology Introduction Classification of Batteries Battery Characteristics Nickel-Metalhydride (Ni-MH) Battery Zinc-Air Battery Li-MnO2 Battery Li-ion Battery Fuel Cells Introduction to Fuel Cells Advantages and Limitations of Fuel Cells Difference between Conventional Cells and Fuel Cells Methanol-oxygen Fuel Cell with H2SO4 as Electrolyte Points to Remember Review Questions from Recent VTU Papers Corrosion and Metal Finishing Corrosion Introduction Electrochemical Theory of Corrosion Factors Affecting the Rate of Corrosion 21 (ix)

11 2.1.4 Galvanic Series Types of Corrosion Corrosion Control Anodizing of Aluminium Phosphating Galvanizing (Anodic Metal Coating) Tinning (Cathodic Metal Coating) Cathodic Protection Metal Finishing Introduction Technological Importance of Metal Finishing Electroplating Decomposition Potential Overvoltage Polarization Factors Influencing the Nature of Electro Deposit Electroplating of Nickel (Watt s Bath) Electroplating of Chromium (Decorative and Hard) Electroless Plating Distinction between Electroplating and Electroless Plating Electroless Plating of Copper for PCB Manufacture Points to Remember Review Questions from Recent VTU Papers 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 Various Constituents of Petroleum Cracking Synthesis of Petrol by Fischer-Tropsch Process Octane Number Reformation of Petrol Mechanism of Gasoline Knocking Anti-knocking Agents Cetane Number Mechanism of Knocking in Diesel Engine 45 (x)

12 Power Alcohol Biodiesel Solar Energy Introduction Utilization and Conversion of Solar Energy Photovoltaic Cells Design of PV Cells: Modules, Panels and Arrays Advantages and Disadvantages of PV Cells Production of Metallurgical Grade Silicon Production of Solar Grade Silicon by Union Carbide Process Purification of Silicon by Zone Refining Doping of Silicon by Diffusion Technique (n and p Types) Points to Remember Review Questions from Recent VTU Papers Polymers Introduction Types of Polymerization Addition Polymerization Condensation Polymerization Mechanism of Free Radical Polymerization Molecular Weight of Polymers Glass Transition Temperature (Tg) Structure-Property Relationship Polymethylmethacrylate (PMMA) or Plexiglass Polyurethane (PU) Polycarbonate (PC) Elastomers Silicone Rubber Adhesives Epoxy Resin Polymer Composites Kevlar Fibre Conducting Polymers Mechanism of Conduction in Polyaniline Points to Remember Review Questions from Recent VTU Papers Water Technology and Nanomaterials Water Technology Introduction 67 (xi)

13 5.1.2 Boiler Troubles Scale and Sludge Priming and Foaming Boiler Corrosion Determination of Dissolved Oxygen (DO) in Water Samples (Winkler s Method) Determination of Chemical Oxygen Demand (COD) of Water Samples Determination of Biological Oxygen Demand (BOD) of Water Samples Numerical Problems on COD Sewage Treatment Softening of Water by Ion Exchange Method Desalination of Sea Water Reverse Osmosis Electrodialysis Nanomaterials Introduction Size Dependent Properties of Nanomaterials Bottom-up Approach for the Synthesis of Nanomaterials Sol-gel Method Precipitation Method Gas Condensation Method Chemical Vapour Condensation Process Nanoscale Materials Carbon Nanotubes Nanowires and Nanorods Fullerenes Dendrimers Nanocomposites Points to Remember Review Questions from Recent VTU Papers 85 Latest Development on Relevant Topics Index (xii)

14 Module 1 Electrochemistry and Battery Technology 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 of electrochemistry, construction, working and applications of batteries and fuel cells that find wide applications in automobiles and electronic gadgets. The students also understand the role of electrodes in qualitative and quantitative measurement of analytes Introduction 1.1 ELECTROCHEMISTRY Electrochemistry is the study of chemical processes that cause electrons to move. This movement of electrons is called electricity, which is generated by movement of electrons from one electrode to another 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 cells 2. Electrolytic cells A 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. 1

15 2 Engineering Chemistry Construction and Working of Galvanic Cell It 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 to measure the cell potential. The salt bridge maintains ionic balance while preventing the mixing of anodic and cathodic solutions (see Figure 1.1). Figure 1.1: Galvanic Cell Example for galvanic cell is Daniel cell: Zn ZnSO4(1M) CuSO4(1M) Cu i.e., Anode Anode solution Cathode solution Cathode where single line is used to indicate different phases and double line to indicate salt bridge.

16 Electrochemistry and Battery Technology 3 equation: At anode: Zinc electrode undergoes oxidation Zn Zn e At cathode: Copper ions undergo reduction Cu e Cu Net cell reaction is obtained by adding anode and cathode reactions as given below: Zn + Cu 2+ Zn 2+ + Cu Electromotive force (EMF) of the cell at standard conditions or E cell = E cathode E anode E cell is calculated using the where E is standard electrode potential measured at standard conditions, i.e., 298K, 1M concentration and 1 atm. Electrode E (in volts) Zn 2+ /Zn 0.76 Fe 2+ /Fe 0.44 Cu 2+ /Cu 0.34 Ag + /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, whereas the Cu electrode (E = 0.34V) acts as cathode Nernst Equation for Single Electrode Potential Nernst equation relates single electrode potential (E) with nature of the metal, concentration of metal ions and temperature. Consider a reversible redox reaction M n+ + ne M A thermodynamic relationship known as Van t Hoff s isotherm equation represented below, can be applied to the above equilibrium to derive Nernst equation, G = G + RT ln K c... (1.1) Decrease in free energy is related to maximum work done, G = Wmax = nfe... (1.2) G = nfe... (1.3) Kc = [product] [reactant] Substitute equations 1.2, 1.3 and 1.4 in 1.1, nfe = nfe + RT ln [M]... (1.4) n [M ] [M] [M n ]

17 4 Engineering Chemistry Divide by nf; substitute ln = log and substitute [M] = 1 (since concentration of pure metal is taken as unity) E = E RT nf 1 log [M n ] By rearranging the above equation, the Nernst equation for single electrode potential is obtained; or E = E RT nf log [M n+ ] E = E log [M n+ ] at 298K n Nernst equation clearly indicates that the potential of a single electrode varies with concentration of metal ions in the solution. Single electrode potential is determined by using a reference electrode Reference Electrodes Reference 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 the following section Calomel Electrode Construction: Calomel electrode is constructed by filling a paste of Hg and Hg 2Cl 2 at the bottom of a narrow glass tube having a porous plug at the bottom end. Liquid mercury is then filled above the paste. To measure the potential of the electrode a platinum wire is dipped in liquid mercury. This narrow glass tube is placed inside an outer glass tube filled with KCl solution. The porous plug at the bottom of outer tube acts as salt bridge. The electrode can be represented as: Hg (l) Hg 2Cl 2(s) KCl (aq) Working: Figure 1.2: Calomel Electrode The net reversible electrode reaction is; Hg 2Cl 2 + 2e 2Hg + 2Cl

18 Electrochemistry and Battery Technology 5 Nernst equation for calomel electrode is found to be; E = E log[cl ] at 298K Its electrode potential is decided by the concentration of chloride ions and the electrode is reversible with respect to chloride ions. Applications: Concentration of KCl E (in volts) Saturated (4M) M M It is used as a secondary reference electrode in the measurement of single electrode potentials. It is used in potentiometric quantitative analysis Ag-AgCl Electrode Construction: It consists of a Ag wire coated with its sparingly soluble salt AgCl, and is immersed in a solution containing Cl ions. Porous plug at the bottom 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 is found to be; E = E log[cl ] at 298K Its electrode potential is decided by the concentration of chloride ions and the electrode is reversible with respect to chloride ions. Applications: Concentration of KCl E (in volts) Saturated (4M) M M 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

19 6 Engineering Chemistry Measurement of Electrode Potential using Calomel Electrode Potential of any electrode can be measured by combining with a calomel reference electrode. For example, the following cell is constructed to measure the potential of Zn electrode. Cell representation: Zn Zn 2+ KCl Hg 2Cl 2 Hg Ecell E cell = E cell = E Zn = E E E cathode E anode SCE E Zn SCE E cell is read from the voltmeter as 1.0V, E Zn = V 1.0V E Zn = 0.76V Electrolyte Concentration Cells Figure 1.5: Concentration Cell Electrolyte concentration cell is a type of galvanic cell that generates electricity when two electrodes of same metal are in contact with solutions of its ions of different concentration. Potential difference arises due to difference in electrolyte concentrations. Example of concentration cell: Cu Cu 2 2 C M Cu C2 0.1M Cu Metal immersed in dilute solution act as anode (C 1 = 0.001M) whereas the metal immersed in concentrated solution act as cathode (C 2 = 0.1M). Cell reactions: At anode: Cu At cathode: Derivation of an Expression for EMF of Concentration Cell Consider the concentration cell shown in the figure. Its EMF is given by, Ecell Nernst equation for anode: Eanode = = Ecathode Eanode E anode 2.303RT nf log C1 Figure 1.4: Measurement of electrode potential using calomel electrode 2 Cu C M + 2e 2 Cu C 2 0.1M + 2e Cu

20 Electrochemistry and Battery Technology 7 Nernst equation for cathode: Ecathode = E cathode 2.303RT nf log C2 Substitute Nernst equation for anode and cathode in Ecell equation: Ecell = (Ecathode Eanode ) 2.303RT nf In concentration cell, anode and cathode electrodes are same, hence cathode E anode E = 0 Therefore the Nernst equation for concentration cell can be written as; or Numerical Problem Ecell = E cell = 2.303RT C log 2 nf C C log 2 n C1 at 298K EMF of the cell Cu CuSO 4 (0.001M) CuSO 4 (X) Cu is V at 25 C. Find X value. It is clear that C1 = 0.001M, C2 = X and n = 2; Apply Nernst equation for concentration cell E cell n Ecell = = log E Antilog cell n X = C Antilog = X = X C log 2 n C1 X C 1 X = 0.103M log C C 2 1 at 298K

21 8 Engineering Chemistry 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 selectively exchanged 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 Glass Electrode Ag/AgCl Figure 1.6: 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 highly conducting glass membrane at the bottom. The glass membrane is selective to H + ions in the solution, and is made up of silicate glass having 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.

22 Electrochemistry and Battery Technology 9 This boundary potential (Eb) arises due to the difference in concentration of H + ions inside and outside of the glass bulb. Eb = log C C 2 1 C 1 = Concentration of H + inside the bulb, is a constant; C 2 = Concentration of H + ouside the bulb. E b = log [C 2] log [C 1] Substitute log [C 1] = K, a constant Then the equation becomes: Substitute log [H + ] = ph Eb = K log [C2] = K log [H + ] The final equation for E b is obtained as, E b = K ph The potential of glass electrode (E G) 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 glass membrane, EAsy E G Substitute E b value; E G E G = E b + E Ag/AgCl + E Asy = K pH + E Ag/AgCl + E Asy = L pH where constant, L = K + E Ag/AgCl + E Asy Determination of ph using Glass Electrode To 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 Hg 2Cl 2 KCl Solution of unknown ph Glass electrode The potential established at the glass electrode is higher than that of the calomel electrode, hence glass electrode is taken as cathode.

23 10 Engineering Chemistry Figure 1.7: Determination of ph Solution of unknown ph E cell = E cathode E anode E cell Substituting for E G value, Ecell = E G E SCE = [L pH] ESCE The above equation is rearranged to obtain the expression for ph, Introduction ph = L ESCE E cell 1.2 BATTERY TECHNOLOGY Battery is a device consisting of one or more galvanic cells connected in series or parallel or both. 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 minor components of battery.

24 Electrochemistry and Battery Technology Classification of Batteries Primary battery: This battery cannot be recharged, because cell reaction is irreversible. Example: Zn-MnO 2 battery, Li-MnO 2 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 are activated by adding sea water. These batteries have high reliability and long shelf life, hence they find applications in missiles and submarines 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; E cell = (E C E A) η A η C ir cell where, ηa and ηc are overpotential at anode and cathode respectively. Overpotentials should be less to derive maximum voltage. R cell is internal resistance of the cell. Internal resistance should also be less to derive maximum voltage. Current: Current is the rate at which electric charge flows in a circuit and is expressed in Ampere. 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 charged cell or battery under specified conditions. It is determined by Faraday s relation: C = WnF M (where, W = weight of active material; F = Faraday s constant; M = Molar mass of active material; 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 to higher electricity storage density when compared with the same amount of Zn. Energy Efficiency: Energy efficiency for a secondary battery is given by: Energy efficiency = Energy released on discharge Energy required to charge 100 Cycle life: The number of charge/discharge cycles that are possible before failure occurs in the case of secondary batteries is called as cycle life. The cycle life of a battery is affected by corrosion in contacts and shedding of active materials from electrodes. Shelf life: It is essential for most batteries to be stored, sometimes for many years, without self discharge or corrosion of electrodes. Shelf life is defined as duration of storage under specific conditions without any loss in performance.

25 12 Engineering Chemistry Nickel-Metalhydride (Ni-MH) Battery Construction: 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 (VH 2, ZrH 2) and hydrogen storage alloy (LaNi 5) function as anode. Polypropylene is used as separator and an aqueous solution of KOH serves as electrolyte. Cell representation: MH KOH(5.35M) Ni(OH) 2, NiO(OH) Working: Anode reaction: MH + OH discharging M + H 2O + e charging Cathode reaction: NiOOH + H2O + e discharging Ni(OH)2 + OH charging Overall reaction: MH + NiOOH discharging M + Ni(OH) 2 charging Applications: These are high energy density batteries used in phones, cameras and electric vehicles.

26 Electrochemistry and Battery Technology Zinc-Air Battery Construction: Zinc powder/koh (Anode) 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: discharging Anode reaction: 2Zn + 4OH 2ZnO + 2H2O + 4e charging Cathode reaction: O 2 + 2H 2O + 4e discharging 4OH charging Overall reaction: 2Zn + O2 discharging 2ZnO charging Applications: These high energy density batteries are used in hearing aids, medical devices, etc.

27 14 Engineering Chemistry Li-MnO2 battery Construction: Figure 1.10: Li-MnO2 Battery In Li-MnO 2 battery, lithium metal is used as anode and heat treated MnO 2 is used as cathode. Lithium salt (LiCl or LiClO 4) 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) O 2 Mn (III) O 2Li + 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 disch arging Li + + e Cathode reaction: Mn (IV) O 2 + Li + + e Overall reaction: Li + Mn (IV) O2 Applications: disch arging Mn (III) O 2Li + disch arg ing Mn (III) O2Li + These high energy density primary batteries are used in electronic watches, toys, etc.

28 Electrochemistry and Battery Technology Li-ion battery Construction: Figure 1.11: Li-ion Battery In Li-ion battery, the anode is made up of layered graphite intercalated with lithium atoms. The cathode is a lithium metal oxide such as LiCoO 2. Lithium salt (LiPF 6) in mixed organic solvent (ethylene carbonate-dimethyl carbonate) is used as electrolyte and non-woven polypropylene is used as separator. Cell representation: Li Li +, C LiPF 6 in ethylene carbonate LiCoO 2 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 through electrolyte to cathode. At cathode, Co 4+ is reduced to Co 3+ and lithium ions are inserted into the layered structure of metal oxide. discharging Anode reaction: Li xc xli + + xe + C charging Cathode reaction: Li 1 xcoo 2 + xli + + xe discharging LiCoO 2 charging Overall reaction: Li xc + Li 1 xcoo 2 discharging LiCoO 2 + C charging During charging, Co 3+ is oxidized to Co 4+ liberating lithium ions and electrons. The electrons flow 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.

29 16 Engineering Chemistry Introduction to Fuel Cells 1.3 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. However the major difference is reactants (fuel and oxidant) are continuously supplied and products are continuously removed, whereas in a battery reactants are stored inside and the products are not removed. Fuel cell is represented as; Fuel anode electrolyte cathode oxidant Advantages and Limitations of Fuel Cells Advantages 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 H 2) need to be stored in tanks at high pressure. It requires expensive catalysts Difference between Conventional Cells and Fuel Cells S.No. Conventional cells (batteries) Fuel cells 1 Reactants are stored inside the cell Reactants are supplied from outside 2 Reaction products are toxic Eco-friendly 3 Secondary cells can be charged It cannot be charged 4 Expensive catalysts not required Expensive catalysts required Methanol-oxygen Fuel Cell with H2SO4 as Electrolyte Construction: In this type of fuel cell, methanol is used as fuel and oxygen is used as oxidant. The anode and cathode are porous nickel sheets coated with electrocatalysts. Pt/Ru catalyst on anode and Pt alone on cathode. Methanol mixed with sulphuric acid is passed through anode chamber. Pure oxygen is passed through cathode chamber. Electrolyte sulphuric acid is placed in the central chamber. To prevent the diffusion of anode reactant methanol into cathode chamber, a proton conducting membrane is placed near cathode. The membrane allows only protons to cathode.

30 Electrochemistry and Battery Technology 17 Working: Anode reaction: CH3OH + H2O Figure 1.12: Methanol-oxygen Fuel Cell CO2 + 6H + + 6e Cathode reaction: O2 + 6H + + 6e 3H2O Overall reaction: CH 3OH O2 CO 2 + H 2O 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 E cell is the potential difference between cathode and anode, E cell = E cathode E 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.

31 18 Engineering Chemistry The electrode potential of calomel and Ag-AgCl reference electrodes are decided by the concentration 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 of same 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 a potential proportional to the concentration of that ions. Example: glass electrode is an ion selective electrode selective to H + ions and is used in ph measurements. Glass electrode is constructed by immersing Ag-AgCl internal reference electrode in glass bulb containing 0.1M HCl. The glass bulb is made of a glass membrane which is selective to H + 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, Battery components and reactions Anode Cathode C = WnF M Table 1.1: Summary of Construction and Working of Various Batteries and Fuel Cell Ni-MH battery Zn-Air battery Li-MnO 2 battery Li-ion battery Methanol-O 2 Fuel Cell Ni grid coated with MH and H 2 storage alloy LaNi 5 Ni grid coated with NiO(OH) Zn powder Li metal Li atoms intercalated in layered graphite Electrolyte KOH solution KOH (6M) LiCl in organic solvent (propylene carbonate + 1,2- dimethoxyethane) Anode reaction Cathode Reaction Overall Reaction MH + OH dis M + char H 2O + e NiOOH + H2O + e dis char Ni(OH) 2 + OH MH + NiOOH d M + c Ni(OH) 2 Ni sheet coated with Pt Porous carbon MnO 2 LiCoO 2 Ni sheet coating with Pt/Ru 2Zn + 4OH dis ch arg 2ZnO + 2H 2O + 4e O2 + 2H2O + 4e dis char 4OH 2Zn + O 2 dis ch arg 2ZnO Li dis Li + + e Mn (IV) O2 + Li + + e dis Mn (III) O 2Li + Li + Mn (IV) O 2 discharging Mn (III) O 2Li + LiPF 6 in mixed organic solvent (ethylene carbonate and dimethyl carbonate dis Li xc char XLi + + xe + C Li1 x CoO2 + XLi + + xe dis LiCoO 2 char Li xc + Li 1 X dis CoO 2 char LiCoO 2 + C H 2SO 4 CH 3OH + 6H 2O CO 2 + 6H + + 6e O 2 + 6H + + 6e 3H 2O CH 3OH O 2 CO 2 + H 2O

32 Electrochemistry and Battery Technology REVIEW QUESTIONS FROM RECENT VTU PAPERS 1. 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 CuSO 4 (0.001M) CuSO 4 (XM) Cu is V at 25 C. Find the value of X. [Dec. 2015] 6. What are concentration cells. The emf of the cell Ag AgNO 3 (0.0083M) AgNO 3 (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 of the 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]