S.CHAND’S - KopyKitab · S. CHAND & COMPANY LTD. (An ISO 9001 : 2000 Company) Head Office: 7361,...

S.CHAND’SAPPLIED CHEMISTRY

VOL.2[According to the Syllabus of 2nd Semester University of Mumbai]

Dr. S.S. DARA M.Sc., Ph.D.

Former Registrar and DirectorBoard of College & University Development

Nagpur University, Nagpur - 440 010(Formerly Director Priyadarshini College of

Engineering and Architecture, Nagpur - 440 016)[Formerly, Professor & Head, Department of Applied Chemistry

Visvesvaraya Regional College of Engineering, Nagpur - 440 011]

Dr. S.D. SHETE M.Sc.Ph.D.

Professor & Head, Department of Engineering Science, Ramrao Adik Institute ofTechnology, Nerul, Navi Mumbai, Visiting faculty-University of

Central Lancashire, UK Visiting faculty-Padmashree Dr. D.Y. Patil University,Nerul, Navi Mumbai

S. CHAND & COMPANY LTD.(AN ISO 9001 : 2000 COMPANY)

RAM NAGAR, NEW DELHI-110 055

Created with Print2PDF. To remove this line, buy a license at: http://www.software602.com/

S. CHAND & COMPANY LTD.(An ISO 9001 : 2000 Company)Head Office: 7361, RAM NAGAR, NEW DELHI - 110 055Phone: 23672080-81-82, 9899107446, 9911310888Fax: 91-11-23677446Shop at: schandgroup.com; e-mail: [email protected]

Branches :AHMEDABAD : 1st Floor, Heritage, Near Gujarat Vidhyapeeth, Ashram Road, Ahmedabad - 380 014,

Ph: 27541965, 27542369, [email protected] : No. 6, Ahuja Chambers, 1st Cross, Kumara Krupa Road, Bangalore - 560 001,

Ph: 22268048, 22354008, [email protected] : 238-A, M.P. Nagar, Zone 1, Bhopal - 462 011, Ph: 4274723. [email protected] : S.C.O. 2419-20, First Floor, Sector - 22-C (Near Aroma Hotel), Chandigarh -160 022,

Ph: 2725443, 2725446, [email protected] : 152, Anna Salai, Chennai - 600 002, Ph: 28460026, 28460027, [email protected] : Plot No. 5, Rajalakshmi Nagar, Peelamedu, Coimbatore -641 004, (M) 09444228242,

[email protected] : 1st Floor, Bhartia Tower, Badambadi, Cuttack - 753 009, Ph: 2332580; 2332581,

[email protected] : 1st Floor, 20, New Road, Near Dwarka Store, Dehradun - 248 001,

Ph: 2711101, 2710861, [email protected] : Pan Bazar, Guwahati - 781 001, Ph: 2738811, 2735640 [email protected] : Padma Plaza, H.No. 3-4-630, Opp. Ratna College, Narayanaguda, Hyderabad - 500 029,

Ph: 24651135, 24744815, [email protected] : A-14, Janta Store Shopping Complex, University Marg, Bapu Nagar, Jaipur - 302 015,

Ph: 2719126, [email protected] : Mai Hiran Gate, Jalandhar - 144 008, Ph: 2401630, 5000630,

[email protected] : 67/B, B-Block, Gandhi Nagar, Jammu - 180 004, (M) 09878651464KOCHI : Kachapilly Square, Mullassery Canal Road, Ernakulam, Kochi - 682 011, Ph: 2378207,

[email protected] : 285/J, Bipin Bihari Ganguli Street, Kolkata - 700 012, Ph: 22367459, 22373914,

[email protected] : Mahabeer Market, 25 Gwynne Road, Aminabad, Lucknow - 226 018, Ph: 2626801,

2284815, [email protected] : Blackie House, 103/5, Walchand Hirachand Marg, Opp. G.P.O., Mumbai - 400 001,

Ph: 22690881, 22610885, [email protected] : Karnal Bag, Model Mill Chowk, Umrer Road, Nagpur - 440 032, Ph: 2723901, 2777666

[email protected] : 104, Citicentre Ashok, Govind Mitra Road, Patna - 800 004, Ph: 2300489, 2302100,

[email protected] : 291/1, Ganesh Gayatri Complex, 1st Floor, Somwarpeth, Near Jain Mandir,

Pune - 411 011, Ph: 64017298, [email protected] : Kailash Residency, Plot No. 4B, Bottle House Road, Shankar Nagar, Raipur - 492 007,

Ph: 09981200834, [email protected] : Flat No. 104, Sri Draupadi Smriti Apartments, East of Jaipal Singh Stadium, Neel Ratan

Street, Upper Bazar, Ranchi - 834 001, Ph: 2208761, [email protected] : Plot No. 7, 1st Floor, Allipuram Extension, Opp. Radhakrishna Towers, Seethammadhara

North Extn., Visakhapatnam - 530 013, (M) 09347580841,[email protected]

© 2010, Dr. S.S. Dara, Dr. S.D. SheteAll rights reserved. No part of this publication may be reproduced, stored in a retrievalsystem or transmitted, in any form or by any means, electronic, mechanical, photocopying,recording or otherwise, without the prior permission of the Publishers.t

!"#$% &'"%"() *+,+

ISBN : 81-219-3353-6 Code : 10 429

PRINTED IN INDIA

By Rajendra Ravindra Printers Pvt. Ltd., 7361, Ram Nagar, New Delhi -110 055and published by S. Chand & Company Ltd., 7361, Ram Nagar, New Delhi -110 055.


PREFACE

It gives us immense pleasure to present this Text Book on Applied ChemistryVol. 2 as per the revised syllabus of Mumbai University which is common to all branchesof Engineering. This book is prepared strictly as the revised syllabus prescribed by theMumbai University.

We have revised this book keeping in mind the academic backgrounds and therequirements of the students of First Year Engineering and Technology. Each chapterbegins with learning objectives and provides clear and succinct knowledge on everytopic to the students. Since it has been observed that students face difficulty in completingthe paper during examination because of time constraint, we have tried to reduce thecontent but we have not compromised the original concepts and retained the same. Minutedetails are dealt with precision in each chapter and different types of numericals areexplained in complete details. Solutions to university questions are provided at the endof each topic. We hope that our endeavour Will enable the students to have completeunderstanding of each and every concept. This book is specifically design to meet thetextual requirement of students.

We have also tried to introduce certain modem concepts and recent developments toenrich the knowledge of students. Simple language is used for the benefits of the students.

We would be extremely happy to receive feedback in terms of suggestion andconstructive criticism from our esteemed readers so that we can bring about improvementin the future editions.

Prof. Dr. S.D. SHETE

(iii)


ACKNOWLEDGEMENT

I sincerely acknowledge the encouragement, moral support and useful suggestion of allthe followings.

RAES, Director-Mr. U.S. Shende; RAIT- Principal – Dr. S.R. Devne, Prof. & Head ofBiotechnology & Bioinformatics – Dr. D.A. Bhiwgade; Dr. Mohan Bhagwat; Dr. J. J. Kadam,Principal S. D. Shah; Dr. (Mrs.) P.A. Mane; Prof. (Mrs.) Khadilkar; Prof. (Mrs.) Dolly Babar,Dr. (Mrs.) Prajakta Deshmukh, Dr. Vina Naik; Dr (Mrs.) Jayshree Parikh; Dr. V.N. Balsaraf;Dr. S.N. Singh, Prof. Mr. Jadhav Prof. Mrs. Preeti Zade; Prof. (Mrs.) Anjali Kirkire;Prof. G. Bhanu Murthy; Prof Rajput M.J., Prof (Mrs.) Anuradha Pawar; Dr. Shanta Sharma;Prof. Harshal Keer, Prof. Pujari J.S.; Prof. N.R. Dasre; Dr. Arpita Pal Choudhary;Prof. (Mrs.) P.P. Patil.

Regional Manager western Region and all the Branch Manager of S. Chand and CompanyLtd. – Mr. Kaushik; Assistant Manager S. Chand & Company Ltd. – D.R. Parab; Mr. Morefor their whole hearted cooperation in all aspects of the publication and promotion of thisbook.

I do not have enough to express my gratitude for the co-operation and theaffectionate support of my family members prof. (Mrs.) P.S. Shete, Pranavkumar and Ruturaj.

Prof. Dr. S.D. SHETE

(iv)


NEW REVISED SYLLABUS OF MUMBAI UNIVERSITY W.E.F.ACADEMIC YEAR 2007 – 08

APPLIED CHEMISTRY – VOL. 21. Corrosion

Nernst theory, Standard Electrode potential, Types of corrosion Dry or chemical corrosionwet or electrochemical corrosion, Electrochemical, Galvanic cell, Concentration cell.Intergranular Stress cell corrosion. Polarization, Over voltage, Factors affecting rate ofcorrosion.

Methods to decrease the rate of corrosion, Cathodic and Anodic protection, Cathodic andAnodic coatings, Advanced coatings and protection methods, Only constituents and theirfunction of (a) Paints (b) Varnishes (c) Lacquers (d) Enamels.

Metallic coatings : Methods of coating and study only, electroplating method. CorrosionEngineering of electronic and photonic devices.

2. AlloysAlloys, Types of alloys, Alloys of Al, Cu and Pb. Their composition properties and uses.Recent advances in alloy related materials.Powder Metallurgy, Methods of metal powder formation, Metal Ceramic powders, Technologyof Powder metallurgy, Applications of powder metallurgy.

3. Fuel Definition, Classification, Characteristic properties of a good fuel, Calorific value, Gross

and Net calorific value, Conversion Proximate and ultimate analysis of fuels, Combustioncalculations for requirement of oxygen and air for given solid, liquid gaseous fuel.

Liquid fuels : Crude Petroleum oil, classification, Separation and purification of Gasolinefrom Crude oil. Thermal cracking, Catalytic cracking. Fixed bed, moving bed method forobtaining gasoline.

Diesel, Bio diesel, methods to obtain bio diesel, production of ethanol using bio-mass.Production of hydrocarbons from plants, Knocking, Octane value, antiknocking agents andtheir function recent technology for catalytic converter.

4. Composite materials Introduction, Constitution, Characteristic properties classification, Particle, Fiber, Reinforced

composites structural composites. Application of composite materials.

5. Green chemistry Introduction, Goals significance, Basic ideas in the field of green chemistry research with

3 examples. Industrial applications of green chemistry.

6. Catalysis : Introduction, Importance of catalysts and adsorbents in industry, Activation energy and

catalysts.

(v)


Molecular design for catalysts and adsorbents, Molecular design by nature-zeolites, zeotypes,pillard clays, metal complexes and clusters, oxide material carbon materials, membranes.

Theory Examination :1. Question paper will comprise of total 7 questions, each of 15 marks.2. Only five questions need to be solved.3. Question 1 will be compulsory and based on entire syllabus.4. Remaining questions will be mixed in nature (for example suppose Q. 2 has part (a) from

module 3 then part (b) will be from any module other than module 3).5. In question paper weightage of each module will be proportional to number of respective

lecture hours as mentioned in the syllabus.

Term Work :Term work shall consist of minimum five experiments and a written test. The distributionof marks for term work shall be as follows :Laboratory work (Experiments and journal) 10 MarksTest (at least one) : 10 MarksAttendance (Practical and Theory) 05 MarksTotal : 25 Marks

The final certification and acceptance of TW ensures the satisfactory performance oflaboratory work and minimum passing in the TW

List of Experiments :1. Estimation of Cu iodometrically.2. Estimation of Zn complexometric titration.3. Estimation of Ni complexometric titration.4. Estimation of Al complexometric titration5. Calorific value of solid or liquid fuel using Bomb calorimeter.6. Preparation of membranes for filter any one. Demonstrate.7. CO2 from air by orsats method.8. Estimation of Fe by gravimetric method.9. Estimation of Ni by gravimetric method.

10. Estimation of Sn iodimetrically.11. Estimation by iodimetrically.12. Preparation of biodiesel from adible oil.13. Synthesis of simple layered materials and their characterization.14. Preparing simple composites and their characterization.

(vi)


CONTENTS1. CORROSION 1 – 68

1.1 Nernst Theory 11.2 Standard Electrode potentials 11.3 Galvanic Series 31.4 Galvanic or Electric Cells 41.5 Concentration Cells 41.6 Reversible Cells 51.7 Polarization 51.8 Decomposition potential 61.9 Overvoltage or over-potential 6

1.10 Current Density 71.11 Corrosion 81.12 Types of Corrosion 91.13 Dry or Direct Chemical Corrosion 91.14 Electrochemical or Wet Corrosion 101.15 Galvanic Cell Corrosion or Principle of Corrosion 111.16 Mechanism of Electrochemical Corrosion 121.17 Concentration Cell Corrosion 141.18 Differential Aeration 141.19 Atmospheric Corrosion 161.20 Factors Influencing Corrosion 171.21 Passivity 211.22 Position of the Metal in the Galvanic series 221.23 Types of Corrosion 221.24 Inter Granular Corrosion 231.25 Stress-Corrosion Cracking 241.26 Water-Line Corrosion 251.27 Soil Corrosion 251.28 Micro-biological Corrosion 261.29 Protection from Corrosion or Corrosion Control 26

1.30.1 Cathodic and Anodic Protection 291.31 Metallic Coatings 34

1.31.1 Galvanizing 341.31.2 Tinning 341.31.3 Metal Spraying 351.31.4 Metal Cladding 361.31.5 Cementation 361.31.6 Electroplating 36

(vii)


1.31.7 Numericals based on Faraday’s law 381.31.8 Inorganic non-metallic Coatings 401.31.9 Organic Coatings 41

1.31.10 Varnishes 441.31.11 Enamels 441.31.12 Lacquers 45

University Questions 45

2. ALLOYS 49 – 612.1 Introduction 492.2 Properties of Alloys 492.3 Alloys of Aluminium 492.4 Alloys of Copper 502.5 Alloys of Lead 522.6 Recent Advances in Alloy Related Materials 522.7 Powder Metallurgy 522.8 Production of Metal Powders 532.9 Mechanical Pulverization 53

2.10 Atomization 532.11 Chemical Reduction 532.12 Carbonyl Process (Decomposition) 532.13 Electrolytic Process 532.14 Compaction and Shaping 542.15 Cold Compaction Methods and Hot Compaction 542.16 Powder injection moulding (PIM) 552.17 Cold Powder extrusion 572.18 Roll Compaction 572.19 Hot Compaction 572.20 Ceramic Powder 582.21 Advanced ceramic materials 602.22 Applications and Properties of Powder - Metallurgy. 602.23 Advantages of powder metallurgy 612.24 Limitations or Disadvantages of powder metallurgy 61

University Questions. 61

3. FUELS 62 – 1013.1 Definition of a fuel 623.2 Classification 623.3 Calorific Value 633.4 Criteria for selecting a fuel 643.5 Solid fuels 65

3.5.1 Wood 653.5.2 Peat 653.5.3 Lignite 66

(viii)


3.5.4 Bituminous coal 663.5.5 Anthracite 67

3.6 Analysis of coal and its significance 673.7.1 Proximate Analysis of coal 673.7.2 Ultimate Analysis 68

3.8 Numerical Problems Based on Analysis of coal 703.9 Dulong’s Formula and Numericals 72

3.10 Numerical Problems Based on Combustion and Fuel Gas Analysis 733.11 Merits and Demerits of liquid fuels 833.12 Petroleum 833.13 Classification of petroleum 843.14 Mining of petroleum 843.15 Refining of petroleum 853.16 Luquified Petroleum Gas (LPG) 873.17 Cracking 883.18 Thermal cracking 883.19 Catalytic cracking 89

3.19.1 Fixed bed catalytic cracking 893.19.2 Fluid bed or moving bed catalytic cracking 90

3.20 Advantages of catalytic cracking over thermal cracking 913.21 Knocking 913.22 Octane Rating of fuels 923.23 Anti-knocking agents 933.24 Unleaded petrol 933.25 Cetane number 943.26 Distinguish between octane and cetane number 953.27 Alternative Diesel Fuels 953.28 Bio-diesel Derived from vegetable oils 953.29 Power alcohol 98


4. COMPOSITE MATERIALS 102 – 1104.1 Introduction 1024.2 Constitution 1024.3 Classification 1044.4 Particle-Reinforced Composites 1044.5 Fiber Glass-Reinforced Composites 1074.6 Other Fibre-Reinforced Plastic composites 1074.7 Metal Matrix-Fiber composites 1074.8 Structural Composites 1084.9 Applications of Composite materials 109

4.10 Tables : Area of Applications of Inorganic Fibers 1094.11 Advantageous Characteristics of composites 110

University Questions 110(ix)


5. GREEN CHEMISTRY 111 – 1285.1 Introduction 1115.2 Twelve Principles of Green Chemistry 1115.3 Goals of Green Chemistry 1125.4 Significance of Green Chemistry 1125.5 Basic components of Green chemistry Research 1135.6 Alternative feedstocks or starting materials 1135.7 Alternative reagents or transformations. 1155.8 Atom Economy 1185.9 Functional Group Approaches to Green Chemistry 120

5.10 Structure-Activity Relationship 1205.11 Elimination of Toxic Functional Group 1215.12 Reducing the bioavailability 1225.13 Designing for Innocous Fate 1225.14 Optimization of Frameworks for the design of Greener Synthetic pathways. 1225.15 Industrial applications of Green chemistry 1245.16 Green Solvents 1255.17 Green fuels and E-Green propellants 1265.18 Conclusion 127


6. CATALYSIS 129 – 1496.1 Introduction 1296.2 Action of a catalyst 1296.3 Characteristics of catalytic reactions 1296.4 Types of catalysis 1326.5 Catalytic promoters 1346.6 Catalytic poisons 1356.7 Negative catalysts and Inhibition 1366.8 Autocatalysis 1376.9 Induced catalysis 138

6.10 Activation Energy and catalysis 1386.11 Theories of catalysis 1396.12 Intermediate compound formation Theory 1396.13 The Adsorption theory 1416.14 Molecular Design of zeolites 1446.15 Metal complex catalyst 1466.16 Pillared Clays 1466.17 Carbon Membranes 147


(x)


“ The secret of effective engineering lies in controlling rather than preventing corrosion because it is impossibleto eliminate corrosion.”

– Michael Henthorne

1.1 NERNST THEORYAccording to Nernst’s theory no metal was truly insoluble, and all metals have a tendency to pass

into solution. Thus, if a piece of copper is immersed in water, some copper atoms will shed theirvalence electrons and the positively charged copper ions, Cu++ go into solution. This leaves anexcess of negative charge on the metal electrode and thus a potential differnce exists between themetal and the solution. The positively charged Cu++ are held near the negatively charged metal piecebecause of electrostatic attraction. The process continues until an equilibrium is established when thenumber of Cu++ ions returning to the copper electrode and regaining two electrons forming Cu atomsis equal to the number of copper atoms going into solution as Cu++ ;

Cu0 – 2c Cu ++

At this stage, the process stops unless this equilibrium is disturbed.If the copper electrode is put into a concentrated solution of a copper salt, there will be a greater

tendency for Cu++ to deposit on the electrode as copper atoms, than for the copper atoms of theelectrode to go into solution as ions. At a particular concentration of the Cu++ in solution, thepotential difference between the metal and the solution will be zero.

Zinc shows a much greater tendency than copper to go into solution in water as Zn++ and, for theequilibrium to be established, a much greater concentration of Zn++ in solution is required. In case ofsodium, the tendency to go into solution as Na+ is still greater. This tendency of a metal to go intosolution as ions when dipped in water is reckoned in trems of its electrode potential.

The relation between the electrode potential and the concentration (or more precisely the “activity”)of the metal ion is given by Nernst’s equation;

0.0591 CE = logn K

where C = concentration (more precisely “ activity”) of the metal ions in gram ions / litre, n= thecharge or valence of the ions and K = equilibrium constant. Obviously, if C = K, the potential is zero.Nernst suggested that the numerical values of K for each ion gave a quantitative estimate of thetendency of the metal to form an electrolytic solution and hence is known as “ Electrolytic solution-tension constant.”

1.2 STANDARD ELECTRODE POTENTIALSTo determine the potential difference between an electrode and a solution, it is necessary to have

another electrode and a solution whose potential difference is accurately known.The two half cells

CHAPTER

1CORROSION

1


2 S.CHAND’S APPLIED CHEMISTRY – Vol. 2

can then be combined to form a voltaic cell, the e.m.f. of which can be directly measured. Since thee.m.f. of the cell is the arithmetical sum or difference of the 2 electrode potentials, the value of theunknown potential can be calculated. The primary reference electrode is the normal or standardhydrogen electrode. This can be prepared by bubbling hydrogen gas at 1 atmosphere pressure overPlatinized platinum, immersed in a solution of hydrochloric acid containing hydrogen ions at unitactivity. by convention, the potential of the standard hydrogen electrode is taken as zero volts at alltemperatures. By connecting the standard hydrogen electrode with a metal electrode in contact with asolution of its ions of unit activity, the standard electrode potentials of various metals are determined.These values are summarized in table 1.1. When metals are arranged in the order of their standardelectrode potentials, it is called “ electrochemical series” of the metals.

Thus, when C = 1, the Nernst equation becoms:

0.0591 1E = logn K

Where Eo is the “Standard Electrode potential”The standard electrode potentials of the metals are also called as standard oxidation potentials,

because the conversion of a neutral atom to a positive ion is called “ oxidation.” Table 1.1 provides aquantitative estimate to the electrochemical series. The greater the negative value of the potential, thegreater is the tendency of the metal to pass into solution in the ionic state. Thus, potassium havinggreater propensity to go into solution has Eo = – 2.92, whereas gold with least tendency to go intosolution has Eo = + 1.42.

Table 1.1: Standard Electrodes Potentials in aquecous solutions (at 25°C)Metal ion Electrode Reaction Standard Electrode Potential

electrode system (Acid Solution) (E0) in volts

Li/Li+ Li+ + e– = Li – 3.045 (Reactive metals)K/K+ K+ + e– = K – 2.925Ca/Ca++ Ca2+ + 2e– = Ca – 2.866Na/Na+ Na+ + e– = Na – 2.714Mg/Mg++ Mg2 + 2e– = Mg – 2.363Al/Al+++ Al3+ + 3e– = Al – 1.662Mn/Mn++ Mn2 + 2e– = Mn – 1.180Zn/Zn++ Zn2+ + 2e– = Zn – 0.763Cr/Cr+++ Cr3 + 3e– = Cr – 0.744Fe/Fe++ Fe2+ + 2e– = Fe – 0.441Cd/Cd++ Cd2+ + 2e– = Cd – 0.441Co/Co++ Co2+ + 2e– = Co – 0.277Ni/Ni++ Ni2+ + 2e– = Ni – 0.25Sn/Sn++ Sn2+ + 2e– = Sn – 0.136Pb/Pb++ Pb2+ + 2e– = Pb – 0.126H2/2H+ 2H+ + 2e– = H2 0.000 (Reference)Cu/Cu++ Cu2+ + 2e– = Cu 0.337Cu/Cu+ Cu+ + e– = Hg 0.522Hg/Hg+ or Hg2/2H+ Hg+ + e– = Hg 0.799Ag/Ag+ Ag+ + e– = Ag 0.800Hg/Hg++ Hg2+ + 2e– = Hg 0.854Pd/Pd++ Pd2+ + 2e– = Pd 0.987Pt/Pt++ Pt2+ + 2e– = Pt 1.2Au/Au+++ Au3+ + 3e– = Au 1.42 (Noble metals)


CORROSION 3

Further, a metal will normally displace any other metal below it in the series from solutions of itssalts and precipitate it in the metallic form. Thus, Mg,Al,Zn or Fe will displace Cu from solutions ofits salts. Similarly, Pb will displace Cu,Hg, or Ag; while Cu will displace Ag.

The standard electrode potential is a quantitative measure of the readiness of the element to actas a reducing agent in aqueous solution; the more negative the potential of the element, the morepowerful is its action as a reducing agent.

It should be emphasized that standard electrode potential values relate to an eqilibrium conditionbetween the metal electrode and the solution of its ions of unit activity. Potentials determined undersuch conditions as referred as “reversible electrode potentials”.

1.3 GALVANIC SERIESAlthough electrochemical series gives very useful information regarding chemical reactivity of

metals, it may not be able to provide sufficient information in predicting the corrosion behaviour in aparticular set of environmental conditions.However, in many practical situations, several side reactionsmay take place which influence the corrosion reactions. In view of this, oxidation potential measurementsof various metals and alloys in common use have been made using standard calomel electrode as thereference electrode and immersing the metals and alloys in sea water. These are arranged in Table 1.2,in decreasing order of activity and this series is known as “ galvanic series”. This gives a more practicalinformation on the relative corrosion tendencies of the metals and alloys. In general, the speed and severityof corrosion depends upon the difference in potential between the anodic and cathodic metals in contact.However, the exact position of a metal or alloy in the galvanic series in relation to its respective corrosiontendency may be still influenced by other interfering factors.

Table 1.2: Galvanic series (on the basis of relative oxidation potentials in sea water)

More Anodic or active (or Corroded end)

MagnesiumMegnesium alloysZincAluminumAluminum alloysLow carbon steelCast ironStainless steel (active)Lead-tin alloysLeadTinBrassCopperBronzeCopper nickel alloysInconelSilverStainless steel (passive)MonelGraphiteTitaniumGoldPlatinum

More cathodic or inactive

Act

ive

(ano

dic)

Nob

leca

thod

ic


4 S.CHAND’S APPLIED CHEMISTRY – Vol. 2

1.4 GALVANIC OR ELECTRIC CELLSThe cells used for electrolysis are called

electrolytic cells while those used for generationof electrical energy from chemical reactions arecalled galvanic or voltaic cells. A galvanic orelectric cell (chemical battery) can be obtainedby combining any two half cells having differentelectrode potentials. Thus if a standard zinc-half cell is coupled with a standard copper halfcell by wire and a salt bridge as shown inFig 1.1 the resulting cell will have a voltage of

Eocu – EoZn = 0.345 – (–0.762) = 1.107 voltsIn the Daniell cell so formed, the electrons flow from zinc electrode to the copper electrode

through the connecting metal wire, while the Cu++ ions in the solution move to the copper cathodeswhere they reduce their electron “ pressure” and get deposited. The electron “ pressure” is maintainedby the generation of the corresponding stream of zinc ions from the dissolution (or “corrosion”) of thezinc anode:

++Zn° Zn + 2e (oxidation)++ –Cu + 2e Cu° (reduction)

For concentrations other than 1 gm ion per liter, the e.m.f. of the cell may be calculated from theNernst equation:

C0.059 CE = log

n K

= 0.059 1 0.059

log + log Cn K n

= 00.059E + log C

nFor example, if the concentration of Cu++ and Zn++ are 0.01 M and 0.1 M respectively, then the

voltage of the resultant Daniell cell would be

Cu Zn++ ++

Cu Zn 0 00.059 0.059E – E = E + log [Cu ] – E + log [Zn ]

2 2

= {0.345 + 0.0295 log 10–2} – {–0.762 + 0.0295 log 10–1}= 0.345 – 0.059 + 0.762 + 0.0295= 1.0775 volts.

1.5 CONCENTRATION CELLSAn electrode potential varies with the

concentration of the ions in the solution. Henceit follows from the Nernst equation that twoelectrodes of the same metal, but immersed insolutions containing different concentrations ofits ions, may form a cell (when connected with awire and salt bridge). Such a cell is Known as aconcentration cell (Fig. 1.2)

The e.m.f. of the cell will be the algebraicdifference of the two potentials. Thus,

Copper

So4

Zine

Salt bridge

H

SO4HH

e e–

e–

e+

+

SO Zn Zn

SO4

Fig.1.1

Salt bridge

e–

e+

e–

e+

FeFe

Fc Fc Fc Fc

Fc

ConcentratedSolution

(C )1

DiluteSolution

(C )2

Fig.1.2 Concentration cell


Applied Chemistry Vol. -II

Publisher : SChand Publications ISBN : 9788121934954Author : Dr. S. S. Dara, Dr.S. D. Shete

Type the URL : http://www.kopykitab.com/product/11697

Get this eBook

20%OFF

http://www.kopykitab.com/Applied-Chemistry-Vol-II-by-Dr-S-S-Dara-Dr-S-D-Shete

S.CHAND’S - KopyKitab · S. CHAND & COMPANY LTD. (An ISO 9001 : 2000 Company) Head Office: 7361,...

Documents

Transcript of S.CHAND’S - KopyKitab · S. CHAND & COMPANY LTD. (An ISO 9001 : 2000 Company) Head Office: 7361,...