Chemistry notes vtu

5/24/2018 Chemistry notes vtu

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Sri Shridevi Charitable Trust( R )

SHRIDEVI INSTITUTE OF ENGINEERIN

AND TECHNOLOGY, TUMKUR-572106

ENGINEERING CHEMISTRYENGINEERING CHEMISTRYENGINEERING CHEMISTRYENGINEERING CHEMISTRY

CLASS NOTESCLASS NOTESCLASS NOTESCLASS NOTES

1. Dr. CHANDRASEKHAR. N

H.O.D of chemistry

2. Miss. SUJATHA.K

3. Miss. SHWETHA S. RAO

NAME :____________________

USN :____________________

BRANCH : ____________________

SECTION : ____________________


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SHRIDEVI INSTITUTE OF ENGINEERING AND TECHNOLOGY.

ENGINEERING CHEMISTRY DEPARTMENT, S.I.E.T., TUMKUR. 1

CONTENTS

UNIT TITLE PAGENO

I CHEMICAL ENERGY SOURCES 04-24

IIELECTROCHEMICAL ENERGYSYSTEMS

25-43

IIICONVERSION AND STORAGE OF

ELECTROCHEMICAL ENERGY44-56

IV CORROSION SCIENCE 57-71

V METAL FINISHING 72-84

VILIQUID CRYSTALS AND THEIRAPPLICATIONS

85-98

VII HIGH POLYMERS 99-115

VIII WATER TECHNOLOGY 116-132

IX MODEL QUESTION PAPER 133-140


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SyllabusSyllabusSyllabusSyllabusPART AUnit - I

Electrode Potential and CellsIntroduction, Differentiation between galvanic and electrolytic cells,

Construction of galvanic cell, EMF of a cell , Origin of single electrodepotential, Sign convention and cell notation, Standard electrodepotential, Derivation of Nernst equation for single electrode potential.Types of electrodes: Reference electrodes Primary and secondary ,Limitations of standard hydrogen electrode, Construction and working ofcalomel electrode and Ag AgCl electrode, Measurement of singleelectrode potential, Numerical problems on electrode potential and EMFof a cell, Ion selective electrode: Glass electrode Construction ,Determination of pH of a solution using glass electrode.

7 Hours

Unit - IIBatteries and Fuel CellsBasic concepts, Battery characteristics, primary, secondary, reservebatteries and super capacitors with examples.Classical batteries: Construction, working and applications of Zn MnO2battery, Lead acid storage battery andNi Cd battery.Modern batteries: Construction and working and applications of Zn air,Ni metal hydride and Li MnO2batteriesFuel cells Differences between battery and fuel cell, construction andworking of H2 O2andCH3OH O2fuel cells

6 HoursUnit - III

Corrosion and its controlElectrochemical theory of corrosion, Galvanic series, Types of corrosion-Differential metal corrosion, Differential aeration corrosion(Pitting andwater line corrosion) , Stress corrosion (caustic embrittlement in boilers),Factors affecting the rate of corrosion.Corrosion control: Inorganic coatings Anodizing and phosphating,Organic coating painting,Metal coatings Galvanizing and Tinning, Corrosion inhibitors, Cathodicprotection.

7 HoursUnit IV


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Metal FinishingTechnological importance, Theory of electroplating, Significance ofPolarization, Decomposition potential and Overvoltage in electroplating.Effect of plating variables on the nature of electrodeposit. Electroplating

process, Electroplating of Copper and Chromium.Distinction between electroplating and electrolessplating,Electolessplating of copper and nickel.

6 HoursPART BUnit - V

Chemical fuels and Photovoltaic cellsIntroduction, Classification of chemical fuels, Calorific value High and

Low calorific values, Determination of calorific value solid or liquid fuelusing Bomb calorimeter, Gaseous fuel using Buoys calorimeter,

Numerical problems.Petroleum Cracking by fluidized catalytic cracking process,

Reformation of petrol, Octane and Cetane numbers. Knocking mechanism and harmful effects. Antiknocking agents TEL, Catalyticconverters Principle and working, Unleaded petrol, Power alcohol andBiodiesel.

Photovoltaic cells Production of solar grade silicon, Doping of silicon,Construction and working of photovoltaic cell, Advantages.

7 HoursUnit - VI

The Phase rule and Instrumental methods of analysisStatement of Gibbs phase rule and explanation of the terms involved,Phase diagram of one component system water system, Condensedphase rule , Phase diagram of two component system- Eutectic Pb Agsystem and Fe C system. Application Desilverization of lead.

Instrumental methods of analysis- Theory , Instrumentation andapplications of Colorimetry, Potentiometry , Conductometry and Flamephotometry.

6 HoursUnit - VII

PolymersTypes of polymerization Addition and Condensation, Mechanism ofpolymerization Free radical mechanism taking ethylene as example.


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Glass transition temperature ( Tg) . Structure property relationship.Types of plastics Thermosetting and thermoplastics. Compoundingresins to plastics, Manufacture of plastics by compression and injectionmoulding, extrusion method.Synthesis and applications of Teflon, PMMA, Polyurethane and Phenol

formaldehyde resins.Elastomers: Deficiencies of natural rubber, Vulcanization of rubber.Synthesis and applications of Neoprene and Butyl rubber, Siliconerubbers.Adhesives: Synthesis and applications of epoxy resins.Polymer composites - Synthesis and applications of Kevlar and Carbonfibers.Conducting polymers Definition, Mechanism of conduction inPolyacetylene and Polyaniline.

7 Hours

Unit - VIIIWater ChemistryImpurities in water, Water analysis Determination of differentconstituents in water Hardness, alkalinity, chloride , fluoride , nitrate ,sulphate and dissolved oxygen by Winklers method. Numerical problemson hardness and alkalinity.Sewage BOD and COD, Numerical problems, Sewage treatment.Desalination of water Reverse Osmosis and Electrodialysis

6 Hours

Text Books1.A text book of Engineering Chemistry P.C. Jain and Monica Jain

Dhanpatrai Publications,New Delhi.

2. Chemistry In Engineering and Technology ( Vol. 1 &2) J.C.Kuriacose and J. Rajaram.

Reference Books1. Principles of Physical Chemistry B.R. Puri , L.R.Sharma & M.S.

Pathania, S. Nagin chand and Co.2.Text Book of Polymer Science F.W. Billmeyer John Wiley & Sons.3. Corrosion Engineering M.G. Fontana Mc. Graw Hill Publications.4. Environmental Chemistry Stanley E. Manahan , Lewis Publishers.5. Polymer Science V.R. Gowariker , Wiley Eastern Ltd.


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U N I TU N I TU N I TU N I T IIII

CHEMICAL ENERGY SOURCES:FUELS

1.1 Define a fuel.Explain the classification of fuels with examples.5 Marks

A fuel is defined as naturally occurring or artificiallymanufactured combustible carbonaceous material which servesparticularly as source of heat and light and also in few cases as a sourceof raw material.Classification of fuelsFuels are classified into a two types.

1) Based on their origin they are classified intoa) Primary fuelsb) Secondary fuels.

a) Primary Fuels: There are naturally occurring fuels which serves assource of energy without any chemical processing.Ex: Wood, Coal, Crude oil, Natural gas, Peat, Lignite, Anthracite..b) Secondary Fuels: - They are derived from primary fuels & serves assource of energy only after subjecting to chemical processing.Ex: Charcoal, Coke, produsergas, Petrol, Diesel etc.,

2) Bases on their physical state fuel are classified into

a) Solidb) Liquidc) Gaseous fuels.

SOLID LIQUID GASEOUS

Primary FuelsWood, Coal,Peat, Anthracite

Crude oil Natural gas.

Secondary Fuels Coke, Charcoal Petrol, Gasoline,Diesel

LPG,

produsergas,Coal gas.

1.2 Define Calorific Value. Explain the types 04 MarksCalorific value is defined as the amount of heat liberated when a

unit mass of fuel is burnt completely in presence of air or oxygen.


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Calorific value is of two types as follows:-1) Higher calorific value. (HCV) or Gross calorific value. (GCV)2) Lower calorific value. (LCV) or Net calorific value. (NCV)

1) HCV: - It is the amount of heat liberated when a unit mass of fuels

burnt completely in the presence of air or oxygen and the productsof combustion are cooled to room temperature. Here it includes theheat liberated during combustion and the latent heat of steam.Hence its value is always higher than lower calorific value.

2) LCV: - It is amount of heat liberated when a unit mass of fuel isburnt completely in the presence of air or oxygen and the productof combustion are let off completely into air. It does not include thelatent heat of steam. Therefore it is always lesser than HCV.

NCV = HCV Latent heat of steam.

= HCV 0.09X % H2X 587 cal/g

1.3. Mention the SI units of calorific value. 2 MarksIn SI system the units of calorific values for solid fuels are

expressed in J/Kg and for gaseous and liquid are expressed in J/m3.

1.4. Explain the determination of calorific value of solid fuelusing Bomb calorimetric method. 6 Marks


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A small quantity of a fuel is weighed accurately (M Kg) and isplaced in the Bomb. The bomb is placed in known amount water taken ina copper calorimeter. The initial temp of water is noted as a t10C with thehelp of thermometer. Oxygen gas is pumped under pressure 20 to 25atm through the O2valve provided.

The fuel is ignited by passing electric current through the wiresprovided. As the fuel undergoes combustion and liberates heat, which isabsorbed by surrounding water. The water is stirred continuously todistribute the heat uniformly and the final temp attained by water isnoted t20C. & gross calorific value of the fuel is calculated as follows:-

Calculation:

Mass of the fuel = M Kg.Initial temp of the water = t10C

Final temp of the water = t20CChange in temp = t = (t2 t1)0CSpecific heat of water = SWater equivalent of calorimeter = W Kg.

GCV = W x S x t J/Kg orM

GCV = (W+w) x S x t J /KgM

NCV = GCV 0.09 x %H2x 587 cal/g

PROBLEMS:1) Calculate calorific value coal samples from the following data.

6 Marks

Mass of the coal = 1g.Water equivalent of calorimeter = 2 Kg.Specific heat of water = 4.187 J/Kg/c.Rise of temperature = 4.80C.

Solution: GCV = W x S x t J/KgM

= 2 x 4.187 x 4.80.001

= 40195.2 KJ/Kg.


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2) A coal sample with 93% carbon, 5% of Hydrogen and 2% Ash issubjected to combustion in a bomb calorimeter. Calculate GCV and NCVGiven that. 6 MarksMass of the coal sample = 0.95gMass of water in copper calorimeter = 2000g.

Water equivalent wt of calorimeter = 700g.Rise in temp = 2.80CLatent heat of = 587 cal/g.Specific heat of water = 1 cal/g/0C

GCV = (W+w) x S x tM

= (2000+700) x 10-3kg x 1 cal/g/0C x 2.80C x 4.1840.95 x 10-3kg

= 33295.83 J/kg.

NCV = GCV 0.09 x %H2x 587x4.184 J/kg.= 33295.83 J/kg 0.09 x 5 x 587 x4.184 J/kg.= 32190.62 J/kg

3) When 0.84g of coal was burnt completely in Bomb calorimeter theincrease in temp of 2655 grams of water was 1.850C if the waterequivalent calorimeter is 156g Calculate GCV.

GCV = (W+w) x S x t

M= (2655+156) x 1.85 x 10-3 x 4.187

0.84 x 10-3= 25921.26 J/Kg

4) Calculate GCV and NCV of a fuel from the following data.Mass of fuel=0.75g, W=350g. t =3.020C, Mass of water = 1150,% H2=2.8. 6 Marks

GCV = (W+w) x t x SM

= (1150+350) x10-x3 3.02 x 4.1840.75 x 10-3

GCV = 25271. 36 KJ/Kg

NCV = GCV 0.09 x H x 587 x 4.184


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= 25271.36 0.09 x 2.8 x 587 x 4.184

NCV = 24652.44 KJ/Kg

5) Calculate calorific value of a fuel sample of a coal form the followingdata. Mass of the coal is 0.6g. Water equivalent wt of calorimeter is2200g. Specific value 4.187 Kg/KJ/C rise in temperature = 6.520C.

3 MarksGCV = (W1+W2) x S x t

M= (2200) x 10-3 x 4.184 x 6.52

0.6 x 10-3

= 100025.49 KJ/Kg.

6) Calculate GCV and NCV of a fuel from the following data.Mass of fuel =0.83g, W=3500g. , W = 385 g, t1 =29.20C, t2 = 26.50C, % H2= 0.7 and S = 4.2 kj/kg/c

6 MarksGCV = (W+w) x t x S

M= (3.5 + 0.385) x (29.2 26.5) x 4.2

0.83 x 10-3

GCV = 53079.39 KJ/Kg

NCV = GCV 0.09 x H x 587 x 4.184

= 53079.39 0.09 x 0.7 x 587 x 4.2

NCV = 52924.07 KJ/Kg


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1.5 Explain the determination of calorific value of gaseous fuelusing Buoys calorimetric method.

Buoys Calorimeter

The calorific value of a gaseous fuel is determined by burning knownvolume of gas in steady flow calorimeter. Water is allowed to passthrough the tubes surrounding the combustion chamber till thetemperatures measured by the thermometers T1& T2 are the same. Thegaseous fuel under steady is introduced into the burner through the gas

inlet at a steady rate recorded by the gas meter. The gas is burnt in thecombustion chamber and the combustion products are passed over thetubes through which water flows at a constant rate of 6-10 cm3 / sec.When a temperature of the apparatus reaches a constant value (i.e whenT2 shows a constant reading the heat released by the combustion of thefuel in an certain interval of time will be equal to the heat absorbed bywater during the same interval of time. Calorific value Q is given by theequation

Q = mass of water x rise in temp. x specific heatVolume of gas burnt

The rise in temperature should be of the order of about 20 K. Vaporscooled by circulating water are further cooled in condenser tubes tocondense water form during the combustion of hydrogen andhydrocarbons in the fuel. Amount of condense water collected in the


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measuring cylinder for the volume of gas burnt could be made use of forcalculating the net calorific value.Observations and calculations:i) Volume of gas burnt at NTP in time t = V m3ii) Weight of cooling water circulated in time t= W kg

iii) Steady temperature of the inflow water = t10Civ) Steady temperature of the outflow water = t20Cv) Rise in temperature = (t2-t1)0Cvi) Weight of water produced from steam condensation = m kg

Heat released by the combustion ofV cm3 of gas fuel = Heat absorbed by waterHCV x V = W (t2-t1)

Higher calorific value of the fuel = W (t2-t1) k cal /m3V

= W (t2-t1) 4.187 kJ/m3

Vm x 587

Latent heat of steam = k cal m3V

W (t2-t1) 4.187 m x 587 x 4.187Lower (net) calorific value of fuel = -

V V

=------------- kJ/m3

Numericals:

1)Calculate gross and net calorific value of a gaseous fuel from thefollowing data obtained from boys experiment:

i) Volume of gaseous fuel burnt at STP ----- = 0.09 m3ii) Weight of water used for cooling ----- = 25.0 kgiii) Temperature of inlet water ----- = 25.00Civ) Temperature of outlet water ----- = 40.00Cv) Weight of water produced by steam condensation ---- = 0.02 kgvi) Latent heat of steam ----- = 587 k cal kg

Solution:W x (t2-t1)

Higher calorific value of the given gaseous sample = x 4.187V


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= 25 x (40-25) x 4.187

0.09= 17445.8 kJ m3

0.02 x 587 x 4.187Heat released in condensing steam =

0.09

Net calorific value = 546.17 kJ m3= HCV latent heat of steam= 17445.8 546.17= 16899.63 kJ m3

2)Calculate the gross and net calorific value of a gaseous fuel at STP from

the following dataVolume of gas burnt =0.02m3Temperature of the gas =293 KMass of water passing through calorimeter =4.5 kgRise in temp =18.5 KAbsolute pressure of gas =101990 N/m2Specific heat of water =4.18J/g/KAmount of water collected =7.5 cm3Latent heat of steam at 288K =2.454 kJm3Solution:

i)Heat absorbed by cold water

=mass of water x specific heat x rise in temp=4.5 kg x 4.18 J/g/K x 18.5 K=4500 g x 4.18 J/g/K x 18.5 K=348000 J or 348 kJ

ii)Reduce the volume of the gas to that at STP using combined gas lawP1V1 P2V2

=T1 T2

101990 N/m2x 0.02 m3 101325 N/m2 x V

=293 K 273 K

V=0.0188 m3

iii) Calorific value, Q=Heat absorbed by cold water

Volume of gas


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=348/0.0188= 18510 k J/m3

iv) Net Q:Water condensed during combustion = 7.5cm3 = 7.5 gram

Latent heat of steam at 288 K = 2.454 kJ/g

Therefore heat to be deducted from gross calorific value7.5 g x 2.454 kJ/g

= 0188 m3

= 979 kJ/m3

Therfore Net Q = 18510 -979 = 17531 kJ/m3

1.6 What is Petroleum cracking? Explain the Fluidized bed catalyticcracking method.

6 MarksCracking is a process that involves breaking of C-C and C-H bonds

in the chains of high boiling hydrocarbons of high molecular weight, toyield simpler, low boiling hydrocarbons of molecular weight.

Fluidized bed catalytic cracking method.

The catalyst such as alumina or zeolyte is finely powered andmixed with steam and it is pumped to cracking chamber. The feedstock


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(gas oil, heavy oil) is preheated to 5000C and forced into the crackingchamber along with the catalyst by a steam blast where a floatingturbulent bed forms.

In cracking chamber the higher molecular weight hydrocarbons arebroken down into simpler fragments. The products are withdrawn and

sent to fractionating column for separation.The catalyst becomes inactive after cracking process. It is sent to

catalyst activation chamber and it is activated by burning carbondeposited on the catalyst by air blast at 6000C. The catalyst can be usedagain and the process is continuous.

1.7 What is Reformation of Petroleum? Explain the Reformation ofPetrol

6 MarksIt is a process of bringing structural modifications in the strait

chain hydrocarbons (with lower octane number) to increase the octane

number and thereby improving the anti-knocking characteristics ofpetrol.

Reforming is a chemical process, which involves modification of thestructure of molecules without much change in the molecular masses.Reformation of petroleum involves the following reforming reactions:

1) Isomerisation.2) Dehydrogenation.3) Cyclisation & dehydrogenation and4) Hydro cracking.

1) Isomerisation: -It is a process of converting the straight chain hydrocarbon

compound of lower octane number into a branched chain hydrocarboncompound of higher octane number.

2) Cyclisation: Straight chain hydrocarbons undergo cyclisationproducing cyclic hydrocarbons which have higher octane number.

Ex. CH3 CH2 CH2 CH2 CH2-CH3

n- Hexane Cyclo hexane


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3) Cyclisation and dehydrogenation: Straight chain hydrocarbonsundergo cyclisation to form cyclic compounds, which further undergoesdehydrogenation to form aromatic compounds.

Ex. CH3 CH2 CH2 CH2 CH2-CH3

n- Hexane Cyclo hexane Benzene

4) Hydro cracking: -Straight chain hydrocarbons undergo hydrocracking in presence of hydrogen and platinum catalyst producing lowmolecular weight gaseous fractions which are removed to improve theoctane number.

1.8 What is Knocking? Explain the Mechanism of Knocking6 Marks

The explosive combustion of petrol and air mixture produces shockwaves in I.C. engine, which hit the walls of the cylinder and pistonproducing a rattling sound is known as knocking.

Mechanism of Knocking

Beyond a particular compression ratio the petrol mixture suddenlyburns into flame. The rate of flame propagation increases from 20 to

25m/s to 2500m/s, which propagates very fast, producing a rattlingsound. The activated peroxide molecules decomposes to give number ofgases products which produces thermal shock waves which hit the wallsof the cylinder and piston causing a rattling sound which is known asknocking.

The reactions of normal and explosive combustion of fuel can begiven as follows taking ethane as an example


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1.9 Define octane number.2 Marks

Octane number is defined as the percentage of isooctane present ina standard mixture of isooctane and n-heptane, which knocks at the

same compression ratio as the petrol being tested.Isooctane is the branched chain hydrocarbon has least knocking

rate, hence its octane number is arbitrarily fixed as 100. N-heptane astraight chain hydrocarbon has highest tendency to knock hence itsoctane number is fixed as zero. Octane number of petrol is 80 means itcontains 80% by volume isooctane and 20% by volume n- heptane.

1.10 Define Cetane number.2 Marks

It is defined as the percentage of cetane present in standardmixture of a cetane and Alfa- methylnaphthalene, which knocks at the

same compression ratio as the diesel fuel being tested.

1.11 What are Antiknocking agents? Explain Leaded & UnleadedPetrol

5 MarksThese are the substances added to petrol in order to prevent

knocking in I.C. Engines.

Ex: TEL Tetra Ethyl led.TML Tetra Methyl led.MTBE Methyl Tertiary Butyl Ether.

Leaded Petrol:The petrol containing TEL or TML as anti knocking agents is

called leaded petrol. TEL or TML are the very good anti knocking agentsbut has some disadvantages as follows.

a)After combustion lead is deposited as lead oxide on pistonand engine walls it leads to mechanical damage.

b) Lead is a poisonous air pollutant.c) It spoils the catalyst used in catalytic converter.

Unleaded Petrol:The petrol, which contains antiknocking agent other than lead, is

known as unleaded petrol.Ex: MTBE is used, as an antiknocking agent in place of TEL orTML and the petrol is known as unleaded petrol.


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1.12 Explain working and principle of Catalytic converterPrinciple: Use of catalytic converter in the internal combustion enginesof automobiles helps in cleaning up the exhaust emissions. Suchconverters built into the automobile engines promote oxidation-reductioncycles and ensure complete combustion of CO, NOx and HC.

Working: The following fig illustrates the action of catalytic converters:use of catalytic converters in 2 stages helps in the elimination ofpollutants from exhaust gases before they are discharged into theatmosphere

REDUCTION STAGE I AIR OXIDATION

STAGE II

HC,CO,NOFrom exhaust

gasesReleased to atmosphere

N2CO2H2O

Pt-H=Platinum hydrogen compoundPt-O= Platinum Oxygen compoundHC=Hydrocarbon, CO=Carbon monoxideNO=Nitrogen oxide, N=NitrogenNH3=Ammonia

Flow chart of Catalytic converters for treating auto missions

i)In the first converter, nitrogen oxides are reduced to nitrogen andammonia in the presence of finely divided catalyst Ptii)In the second converter, air is introduced to provide an oxidizingatmosphere for complete oxidation of CO & HC into CO2and H2O in thepresence of Pt catalyst

1.13 Explain the manufacture of Synthetic petrol by BergiusProcess?

6 MarksCoal is considered as black diamond because of its high utility value. Theprincipal elements present in coal are carbon and hydrogen. It is

Pt-H+NO Pt-

O+N2+NH3

Pt-O+HC+CO Pt-

H+CO2+H2O


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therefore coal can be converted into liquid hydrocarbons from whichmuch demand and needed petrol can be obtained.

The synthetic petrol can be manufactured by the followingmethods.

1) Direct hydrogenation of coal.(Bergius process)2) Direct hydrogenation of coal.(Fischer-Tropsch process)

Bergius process: (Direct conversion of coal)In this method the lignite is grinded into a fine powder. This powder ismixed with heavy oil & made into a paste. Iron oxide or nickel is addedas catalyst. The mixture is pumped into a reactor. The temperature of thereactor is maintained about 500-5500C & a pressure is maintainedabout 250 atmospheres. H2 gas is passed through the reactor. Ligniteunder goes hydrogenation to form a mixture of hydrocarbons. Thesemixture of hydrocarbons are passed through a fractionating column to

for separation to obtain synthetic petrol.

2) Fischer-Tropsch process: (Indirect conversion of coal)This method involves the following steps

a) Production of water gas:Water gas (CO+H2) is obtained by passingsteam over white hot coal.

C + H2O (g) CO + H2(water gas)b) Production of synthesis gasthe water gas obtained above is freed from dust, H2S and organic Sulfurcompounds and blended with hydrogen to form synthesis gas (CO + 2H2).c) Hydrogenation of carbon monoxide:the Synthesis gas (CO + 2H2) iscompressed to 5-10 atm pressure and admitted into a catalytic reactor.


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containing the catalyst (mixture of cobalt (100 parts), thoria (5 parts) andmagnesia (8 parts)). The reactor is heated to about 2500C.Hydrogenation, reactions takes place to form saturated and unsaturated.These mixture of saturated and unsaturated hydrocarbons are passedthrough a fractionating column to for separation to obtain synthetic

petrol.

1.14 What is Power alcohol? Explain the advantages4 Marks

A mixture of ethyl alcohol and gasoline blend, which can be usedas fuel in internal combustion engine, is known as power alcohol orgasohol.

Absolute alcohol is mixed with ether, benzene etc compounds andone volume of this is mixed with four volumes of petrol and is used as afuel.

Advantages: The power out put is good.

It has better antiknock property. Ethanol is biodegradable; hence it is environmental friendly fuel. The use of ethanol in alcohol increases the oxygen content of the

fuels and promotes more and complete combustion ofhydrocarbons in gasoline.

It reduces carbon monoxide emission.


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1.15Bio diesel:Biodiesel refers to a vegetable oil- or animal fat-based diesel fuelconsisting of long-chain alkyl (methyl, propyl or ethyl) esters. Biodiesel istypically made by chemically reacting lipids (e.g., vegetable oil, animal fat(tallow)) with an alcohol.

Biodiesel is meant to be used in standard diesel engines and is thusdistinct from the vegetable and waste oils used to fuel converted dieselengines. Biodiesel can be used alone, or blended with petrodiesel.


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SOLAR ENERGY

1.16 What is solar energy? Mention the advantages &

disadvantages of solar energy. 4 MarksThe radiations reaching earth from the sun and converting them in todifferent useful forms of energy is called solar energy.The utilization of solar energy is of two types Direct solar power andindirect solar power.

Advantages: The Solar power is pollution free.

It can operated with little maintenance or intervention after initialsetup.

The Solar power is becoming more and more economical as costs

associated with production decreases, and the technology becomesmore effective in energy conversion.

The Solar power can be viewed as a local resource because oforiginal climatic variances.

Disadvantages: The Solar power is only practical in certain areas with a favorable

climate and latitude. That is, areas near the tropics and which arerelatively cloud free.

The Solar power is not available at night. The Solar power decreases during cloudy. The Solar power must be converted into some other form of energy

to be stored. Solar cell technologies produce DC power which must be converted

to the AC power.

1.17 What are photovoltaic cells? 2 MarksPhotovoltaic cells or Solar cells are the semiconductor devices

which converts sunlight into direct current electricity on illumination.

1.18 Explain the working of photovoltaic cells?

6 MarksThe Solar cells or Photovoltaic cells are made out of

semiconductors which have the capacity to absorb light. When n-typeand p-type semiconductor are bought together a semiconductor diode isformed. The semiconductor diode separates and collects the carriers andconducts the generated electrical current preferentially in a specificdirection.


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A typical silicon photovoltaic cell is composed of a thin waferconsisting of an ultra thin layer of phosphorus doped. (n-type) silicon ontop of boron doped (p-type) silicon. Hence a p-n junction is formed. Ametallic grid forms one of the electrical current contacts of the diode andallows light to fall on the semiconductor between the grid lines. An

antireflective layer between the grid lines increases the amount of lighttransmitted to the semiconductor. The cells other electrical contacts isformed by a metallic layer on the back of the solar cell.

When light radiation falls on the p-n junction diode, electron holepairs are generated by the absorption of the radiation. The electrons aredrifted to and collected at the n-type end and the holes are drifted to p-type end. When these two ends are electrically connected through aconductor, there is a flow of current between the two ends through theexternal circuit. Thus photoelectric current is produced.

1.19 Explain the Importance of Photovoltaic cells: 6 Marks The conventional energy exhaustible and depleting. Where as Solar

energy being ultimate, inexhaustible and renewable energy. Therethe photovoltaic cells are important means to utilize thiscontinuous energy source.

The Photovoltaic cells can serve for both off-grid and on-gridapplications. It can be used for off-grid professional devices andsupply systems such as telecommunication equipment, solar homesystems, etc.

The Photovoltaic energy conversion environmental friendly as thereis no harmful emission of pollutants.


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Use of or production of solar energy doesnt produce noisepollution.

The electricity obtained from solar energy is useful in minimizingglobal warming due to carbon dioxide.

Photovoltaics can be used as roof integrated systems, providing

power and also serving as optical shading elements for the spacebelow and preventing overheating in the summer.

Photovoltaic cells provide power for spacecraft and satellites.

Developments in the field of photovoltaic cells will boost thesemiconductor industry and storage battery industries.

Silicon:The most common material used for solar cells is crystalline silicon, withmulticrystalline silicon is most used. Silicon is the second member in thegroup IV A in the periodic table. It never occurs free in the nature, butoccurs as oxides and silicates.The solar cells are made out of three primary categories of crystallinesilicon as follow.i) Single crystalline or mono crystalline wafers.ii) Poly or multi crystalline wafers.iii) Ribbon silicon-drawn from molten silicon, having a multicrystalline

structure.

1.20 Explain the Physical properties of Silicon relevant toPhotovoltaic 6 Marks

i) Silicon is a semiconductor with a band gap of 1.12 eV at 250C.ii) Silicon crystallizes into a diamond cubic structure at atmospheric

pressure.iii) Usually metals expand on heating and contract on cooling but silicon

Contracts on melting and expands during solidification.iv) Silicon can be made into semiconductor by adding impurities.

(Providing either free electrons or holes). Impurities from VA group aren-dopants and impurities from IIIA group are p-dopants.

v) Silicon has relatively high refractive index which limits the opticalapplications of silicon. There fore it is coated with antireflectiveagent.

vi) Silicon is brittle even when alloyed with small quantities of impurities.

vii) Shaping for photovoltaic applications require sawing and grinding.


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1.21 Explain the Chemical properties of silicon relevant toPhotovoltaic 6 Marks

i) Silicon is stable in the tetravalent state and has a strong affinity foroxygen, forming stable oxides and silicates. Elemental silicon readily

oxidizes, forming a thin protective film of silica (SiO2).ii) Silicon and carbon from a strong Si-C bond and stable products.Silicon carbide also finds various applications in photovoltaics andelectrons. Primary uses exploit the abrasive properties of SiC for waferingsilicon crystals. Silicon forms hydrides, and monosilane (SiH4) is a keychemical compound for the production of amorphous silicon and thepurification of silicon to semiconductor grade.iii) The chemical reactivity of silicon with chlorine is also very important.Trichlorosilane and tetrachlorosilane are both the intermediates and theby-products of the purification processes in upgrading metallurgicalgrade silicon to semiconductor grade, as these compounds are volatile at

low temperature and can be decomposed to elemental silicon at highertemperature. Other chlorosilanes or halogenosilanes are also used inchemical vapor deposition applications. Silicon and germanium areisomorphism and mutually soluble in all proportions.

1.22 Explain the production of semiconductor grade silicon?6 Marks

Production of semiconductor grade silicon involves the following threestages.i) Production of metallurgical grade silicon (Carbo thermic reductionof silica)

Metallurgical grade silicon of purity of 98.5% Si is produced insubmerged electrical arc furnace. The furnace consists of a crucible filledwith quartz and carbon (metallurgical coke or coal). Silicon is formed asfollows.

SiO2+ 2C(s) Si (I) +2CO (g)Silicon is formed as molten state and is tapped from the bottom of thefurnace. The carbon monoxide further oxidized to carbon dioxide andreleased into the atmosphere.ii) Refining of silicon:The crude silicon obtained in the above method is taken in a large ladleand treated SiO2 and lime/limestone (CaO/CaCO3). The less nobleelements than silica such as Al, Ca and Mg are oxidized as their oxides.


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iii)Production of semiconductor grade silicon

The metallurgical grade silicon obtained in the above process is furtherprocessed in four stages to get semiconductor grade silicon orpolysilicon.

1. Synthesis of silicon hydride.2. Purification of the hydride.3. Decomposition to elemental silicon.4. Removal of byproducts.

The metallurgical grade silicon is treated with dry HCl gas at 3000C to

form trichlorosilane & a small amount of tetrachlorosilane. The mixtureis distilled to get pure trichlorosilane.

The tetrachloro silane (SiCl4) is reduced with hydrogen at 10000in areactor to get tri chloro silane (HSiCl3).

The tri chloro silane is then passed through fixed bed columns

containing quaternary ammonium ion exchange resins catalysts.

The products obtained in the above process are separated by distillation.Tetrachlorosilane & trichlorosilane are again recycled to thehydrogenation reactor & the exchange resin respectively. Silicon hydrideor silane is further purified by distillation & passed into a reactorcontaining heated silicon seed rods. Silane gets pyrolysed to formpolysilicon (semiconductor grade silicon)

1.23 Explain the Doping of Silicon6 Marks

The process of incorporating the desirable impurities in the crystals ofsemiconductors to get desirable extrinsic semiconductor properties asknown as doping techniques.


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Doping of Silicon can be carried out as follows.

i) Doping during crystal formation

Doping can be carried out at the crystal formation stage itself, by addingcalculated amount of dopants into the melt. When silicon is deposited onto the surface of silicon rod by vapor decomposition, doping can beaccomplished by simultaneously depositing a dopant with thesemiconductor material. This can be done by mixing the reaction mixturegas feed with vapors of suitable compounds of the dopant. For example,calculated amount of PH3is mixed with the gas feed to get n-type doping

and BH3for p-type doping.

ii) Diffusion technique:

In this technique, a region of semiconductor material is incorporatedwith dopant atoms by the diffusion of impurity atoms into the crystal ofthe material without actually melting it. By this technique, the extent ofimpurity penetration can be controlled to a very small thickness of thematerial. For example, a n-type silicon can be obtained by heating asilicon wafer below its melting point in an atmosphere of n-typeimpurities such as phosphorus. The impurity atoms considered on the

surface of the wafer diffuses into the crystal. Similarly p-type silicon canbe obtained by heating in an atmosphere of p-type dopants. The extent ofdiffusion can be regulated by controlling the temperature and theconcentration of the impurity atoms.

iii) Ion Implantation technique:

In this technique, the semiconductor is impacted with an ion beam ofimpurity ions. This results in the implantation of some dopants atomsinto the semiconductor crystal. Extent of implantation is controlled bythe energy of the ion beam.


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Objective type questions:

1) Bomb-calorimeter is used for determining the calorific value ofa) Solid fuel b) liquid fuel

c) Gaseous fuel d) both solid fuel & liquid fuel

2) Octane number is related to the petroleum producta) Diesel b) Kerosene c) Petrol d) Lubricating oil

3)The process by which the higher hydrocarbons are broken intolower hydrocarbons by the application of heat by

a) Combustion b) Cracking c) Sparking d) jetting

4) Quality of Diesel fuel is determined bya) Octane rating b) Percentage of Carbon

c) Length of Hydrocarbon chain d) Cetane number

5)The tendency of Knocking is high ina) Aromatics b) Olefinsc) Straight chain hydrocarbons d) Cycloparaffins6) A device in which electricity is produced using Solar energy iscalleda) Fuel cell b) Voltaic cell c) Photovoltaic celld) Concentration

cell

7) Knocking is due to

a) Slow combustion b) Instantaneous explosive combustionc) Incomplete combustion d) All

8) Which of the following is the primary fuela) Producer gas b) Coal gas c) Petroleum d) Water gas

9) HCV is always----------- than NCV


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a) Less b) More c) Equal d) Not related

10) Main constituent present in photovoltaic cells area) Silicon b) Sand c) Carbon d) Iron

11) Unit of Calorific Value isa) g/cc b) Cal/ml c) kJ d) kJ/Kg

12) The Knocking tendency of Hydrocarbon decreases in the followingorder

a) Straight chain> Cyclo alkanes > Aromatic > Branched Chainb) Straight Chain > Branched Chain > Cyclo Alkanes > Aromaticc) Aromatic > Cyclo Alkanes > Branched Chain > Straight Chaind) Cyclo Alkanes > Aromatic > Branched Chain > Straight Chain

13) The catalyst employed in the fluidized catalytic cracking isa) Al2O3+ SiO2 b) Fe2O3+ SiO2c) ZrO2+ SiO2 d) TiO2+ SiO2

14) In photovoltaic cells solar energy is utilized to transforma) Solar energy into light and heat energyb) Solar energy into electrical energyc) Solar energy into electrical chemical energyd)All the above

15)In Fischer- tropsch process of preparation of synthetic petrol --------is used as raw material

a) CO+H2 b) CO2+H2 c) CO+H2O d) CO2+H2O


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REVIEW QUESTIONS1. Define a fuel. Explain the classification of fuels with examples.2. Define calorific Value. Explain the types of calorific value.3. Mention the SI units of calorific value.

4. Describe the Bomb calorimetric method of determination of calorificValue of solid fuel.

5. What is petroleum cracking? Explain the process of fluidized bedCatalytic cracking method

6. What is reformation of Petroleum? Give the reactions involved inreforming.

7. What is Knocking? Explain its Mechanism8. Define octane number.09. Define cetane number.10. What are anti knocking agents? Explain leaded and unleaded petrol.11. What is synthetic petrol? Explain the production of synthetic petrol

12. What is power alcohol? Give its advantages as fuel.13. What are photovoltaic cells?14. Explain how a photovoltaic cell works?15 Explain the Chemical properties of silicon relevant to Photovoltaic16 Explain the Physical properties of Silicon relevant to Photovoltaic17. Explain the production of semiconductor grade silicon18. Explain the Doping of Silicon?


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U N I TU N I TU N I TU N I T IIIIIIII

ELECTRO CHEMICAL ENERGY SYSTEMS

ELECTRODE POTENTIAL AND CELLS

2.1 What is an electrochemical cell Explain the classification withexamples 5 Marks

An electrochemical cell is a device, which is used to convertchemical energy into electrical energy and vise versa.These electrochemical cells are classified into two types as follows.

1) Galvanic or Voltaic cells:These are the electrochemical cells, whichconverts chemical energy into electrical energy.

Ex. Daniel cell, Dry cell, etc.2) Electrolytic cell:These are the electrochemical cells, which are used

to convert electrical energy into chemical energy.

Ex: Lead acid battery, Nickel cadmium battery etc.,Galvanic or Voltaic cells:Galvanic or Voltaic cells are again classified into three types as follows

a) Primary cells: These are the cells which serve as a source of energyonly as long as the active chemical species are present in the cell.The cell reactions are irreversible. These are designed for only singledischarge and cannot be charged again.Ex: Dry Cell, Zn Hgo cell, Zn-Ag2o cell etc.

b) Secondary cells: These cells are chargeable and can be used again

and again. The cell reactions are reversible and are often called asreversible cells. During discharging the cells acts like voltaic cellconverting chemical energy into electrical energy. During charging thecell acts like electrolytic cell by converting electric energy into chemicalenergy, hence these batteries are called as storage battery.

Ex:Lead acid Battery, Ni-cd cells. Lithium ion cells etc.


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c) Concentration of cells:These are the electrochemical cells consisting of same metal

electrodes dipped in same metal ionic solution in both the half cells butare different in the concentration of the metal ions.Ex:copper concentration cell, Zinc concentration cell

2.2 Explain the construction and working of Daniel cell6 Marks

The Daniel cell consisting of two half cells in which zinc and copperelectrodes are immersed in zinc Sulphate and copper Sulphate solutionrespectively. The two half cells are internally connected by a salt bridgeand externally by a metallic wire. The zinc electrode undergoes oxidationand looses electron. The electron liberated migrates to another half cell.

OxidationZn (s) Zn2 + + 2e-

In the other half-cell the cupric ions accepts the electrons,undergoes reduction, and get deposited on copper electrode as copper

atoms.

ReductionCu++(aq) + 2e- Cu (s)


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Due to the above simultaneous oxidation and reduction reactions theDaniel cell generates electrical current, which is indicated by voltmeter orammeter. The Daniel cell can be represented as

Zn (s) /Zn2+(aq) //Cu2+(aq) /Cu.

2.3 Mention the Cell notations and Cell ConventionsCell notations 4 Marks/ Single vertical line represents phase boundary between the metal

and its solution.

// Double vertical line represents salt bridge.

Arrow mark indicates the direction of flow of electrons.

Cell Conventions

i) The half cell which undergoes oxidation is always written towards leftside of the salt bridge.

ii) The half cell which undergoes reduction is always written towardsright side of the salt bridge.

iii) If the direction of arrow mark indicates from left to right. Theelectrons flow from anode to cathode and the cell reactions are

spontaneous and if the direction of arrow mark indicates from right toleft, then electrons flow from cathode to anode. Then cell reactions arenon spontaneous.

iv) The term electrode potential always refers to the reduction potential.

2.4 Define Single electrode Potential. 2 MarksIt is defined as the potential developed at the interphase between

the metal and the solution, when a metal is dipped in a solutioncontaining its own ions. It is represented as E

2.5 Explain the origin of electrode Potential: 6 MarksWhen a metal is dipped in a solution containing its own ions, the

metal may undergo oxidation by loosing electrons or the metal ions mayundergo reduction and get depositing metal atoms on the metal surface.

Consider a metal M is dipped in a solution containing its ions Mn+.


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The tendency of metal to pass in to solution (oxidation) can berepresented as,

M Mn+ + ne-Simultaneously the metal ions from the solution tend to deposit on

the metal as metal atoms (reduction)

Mn+ + ne- M

The above two opposite tendencies will results in equilibrium as follows

Mn+ + ne- M

When a metal undergoes oxidation it loses positive ions intosolution leaving behind a layer of negative charges on its surfaces. Thislayer attracts positive changes and forms an electric double layer (EDL)because of the formation of EDL electrode potential arises.

When metal ions undergo reduction depositing metal atoms on themetallic surfaces the metal surface becomes positively charged. Theaccumulated positive charge on the metal surface attracts a layer of vecharges and forms an electrical double layer or Helmotz EDL whichcauses the origin of electrode potential.

2.6 Explain the measurement of electrode potential 4 Marks

The electrode potentials of any metal electrodes can be determinedby using reference electrodes like standard hydrogen electrode. (SHE).

The SHE is coupled with the electrode whose electrode potential is

to be determined and the electrode potential of the electrode isdetermined by fixing the electrode potential and SHE as zero [at alltemperatures]

Example: Consider the determination of Single electrode potentialof Zinc electrode using Standard Hydrogen electrode.

To determine the Single electrode potential of Zinc electrode it iscoupled with Standard Hydrogen electrode as follows


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The electrode potential of Zinc electrode can be calculated asE cell= E cathode E anodeE cell= E SHE E Zn0.76 = 0 - E ZnE Zn = -0.76 V

The electrode potentials can also be determined by usingsecondary reference electrode such as calomel electrode and Ag / Agclelectrode.

2.7 Define electron motive force. (EMF) 2 Marks

It is defined as the potential difference between the two electrodesof a galvanic cell which causes the flow of current from an electrode withhigher reduction potential to the electrode with lower reduction potential.It is denoted as E cell.

E cell = E right E left.E cell = E cathode E anode.

Problems:1) Calculate emf of a cell constructed by combining Cu & Zn electrodes

dipping in their respective ionic solutions. The standard electrodepotential of Cu and Zn are 0.34 V and 0.76 V respectively at 298K.

E cell = E cathode E anode= Ecu Ezn= 0.34 (-0.76) = 1.1volt

2.8 Define Standard electrode potential. 2 Marks


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It is defined as potential developed at the interface between themetal and the solution. When a metal is dipped in a solution containingits own ions of unit ion concentration and at 298K. [If the electrodesinvolve gases then it is one atmospheric pressure] It is denoted as E0

2.9 Derive Nernst Equation for single electrode 6 Marks

In 1889 Nernst derived a quantitative relationship between theelectrode potential and the concentrations of metal ions are involved.

The maximum work available from a reversible chemical process isequal to the maximum amount of electrical energy that can be obtained;it shows decrease in free energy.Wmax = W eleWmax = - G.The amount of electrical energy available from a cell is equal to theproduct of no of coulombs and volts (energy).

Electrical energy = Volts x coulombsThe number of coulombs of current is the product of number of

moles of electrons that flow and Faradays constants. Number of volts orenergy is the E

W max = W ele = - n x F x E.(No. of moles of electrons) x(Faradays constant) x (No.of volts or

energy).


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Where,E = Electrode potentialE0= standard electrode potentialn = no. of electrons[Mn+] = Concentration of metal ions

R = Universal gas constantT = Temperature(In Kelvin).


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Problems:

1) Calculate the emf of the cell Fe / Fe++ (0.01) // Ag+(0.1) /Ag at 298K ifstandard electrode potentials of Fe and Ag electrodes are 0.42 and 0.8

V respectively.6 Marks

E0cell = E0cathode E0anode

= E0 Ag+/Ag E0Fe++/ Fe

= 0.8 ( 0.42)

= 1.22 V.

= E0cell + 0.0591 log10 [Ag+] 2

n [Fe++]

= 1.22 + 0.0591 log10 (0.1) 2

2 (0.01)

= 1.22 + 0.02955 log 1

= 1.22 V.

2) A cell is constructed by coupling Zn electrode dipped in 0.5 MZnSO4and

Ni electrode dipped in 0.05 M NiSO4. Write the cell representation, cellreaction. Calculate the EMF of cell, given that reduction potentials of Znand Ni as 0.76 and 0.25 volt respectively.

6 MarksCell representation: Zn / ZnSO4(0.5M) // NiSO4( 0.05M) / Ni.Cell reactions: Zn (S) + Ni++(aq) Zn++(aq) + Ni (S)

E0cell = E0cathode E0anode

= E0Ni++/Ni E0Zn++/Zn

= 0.25 ( 0.76)

= 0.51 V.


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= E0cell + 0.0591 log10 [Ni++]

n [Zn++]

= 0.51 + 0.0591 log10 (0.05)

2 (0.5)

= 0.51 + 0.02955 log 0.1

= 0.4805 V.

3) Calculate the potential of Ag Zn cell at 298 K if the concentrations ofAg+ and Zn++ are 5.2 x 106M and 1.3 x 10 3M respectively. E0of the cellat 298K is 1.5 V. Calculate the change in free energy G for thereduction of 1 mole Ag+. 1 faraday = 96.5 k J/ V / mole.

6 MarksCell reaction: 2Ag+(aq) + Zn (S) Zn++(aq) + Ag (S)

= E0cell + 0.0591 log10 [Ag+] 2

n [Zn++

]= 1.5 + 0.0591 log10 (5.2 x 106 ) 2

2 (1.3 x 10 3 )

= 1.5 + 0.02955 log (20 x 109)

= 1.2729 V.

For the reduction of 2 moles of Ag+ions, 2 electrons are requiredFor the reduction of 1 mole of Ag+ions, 1 electron is required

G = n F E cell.= 1 x 96.5 x 1.2729

= 122.83 K J / mol


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4) A cell is constructed by coupling Ni electrode dipped in 0.01 MNiSO4and Pb electrode dipped in 0.5 MPbSO4. Write the cell representation,cell reactions. Calculate the EMF of cell, given that reduction potentialsof Ni and Pb are 0.24 and 0.13 volt respectively.

6 Marks

Cell representation: Ni / Ni++(0.01 M) // Pb++(0.5M) / Pb.

Cell reactions: At anode Ni Ni++ + 2e-At cathode Pb++ + 2e-Pb

Net cell reaction: Ni (S) + Pb++(aq) Ni++(aq) + Pb (S)

E0cell = E0cathode E0anode= E0 Pb++/Pb E0Ni++/Ni= 0.13 ( 0.24)= 0.11 V.

= E0cell + 0.0591 log10 [Pb++]n [Ni++]

= 0.11 + 0.0591 log10 (0.5)2 (0.01)

= 0.11 + 0.02955 log 50= 0.1602 V.

2.10 What are concentrations cells? Explain with an example6 MarksThese are the galvanic cells consisting of same metal electrodes

dipped in same metal ionic solution in both the half cells but aredifferent in the concentration of the metal ions.

Ex:Consider the following concentration cell constructed by dipping twocopper electrodes in CuSO4 solutions of M2 molar and M1molar whereM2M> M1M.

The two half-cell are internally connected by a salt bridge and

externally connected by a metallic wire through voltmeter or ammeter.


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The electrode, which is dipped in less ionic concentrationssolutions (M1) act as anode and undergoes oxidation. The electrode,which is dipped in more ionic concentration (M2) act as cathode andundergoes reduction.

At anode : Cu (S) Cu2+(M1) + 2e-

At cathode : Cu2+(M2) + 2e- Cu (S)_____________________________________________________NCR Cu2+ (M2) Cu2+(M1)

Eof cell = Ecathode Eanode.E cell = [ Eo+ 0.0591 log (M2) ] [Eo+ 0.0591 log (M1)]

n n

Where, (M2) > (M1)


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Problems:1. Calculate emf of the following concentration cell at 250C

Ni (S) / Ni++ ( 0.01M) // Ni++ ( 0.1M) / Ni (S)4 Marks

Where, (M2) > (M1)

E cell = 0.0591 log (0.1)n (0.01)

= 0.02955V

2. Calculate emf of the following concentration cell at 250CCu (S) / Cu++ (0.05M) // Cu++ (5M) / Cu (S)

4 Marks

Where, (M2) > (M1)

E cell = 0.0591 log (5)n (0.05)

= 0.0591V

2.11 Mention the different types of single electrodes4 Marks

i) Metal-Metal ion electrodeThese electrodes consists of a metal dipped in a solution of its ownions.Example: Zn/Zn++

Cu/Cu++

Ag/Ag+

ii) Metal-Metal salt electrode

These electrodes consists of a metal in contact with a its saltExample: Calomel electrode (Hg/Hg2Cl2/Cl-)

Silver Silver Chloride electrode(Ag/AgCl/Cl-)Lead Lead sulphate electrode(Pb/PbSO4/SO4-)


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iii) Gas electrodeExample: H2electrode (H2/Pt/H+)

Chlorine electrode (Pt/Cl2/Cl-)

iv) Amalgam electrodeExample:Lead amalgamelectrode(Pb-Hg/Pb+)

v) Oxidation Reduction electrodeExample: Pt/Fe2+, Fe3+

Pt/Ce3+, Ce4+Pt/Sn2+, Sn4+

vi) Ion selective electrodeExample: Glass electrode

2.12 What are Reference Electrodes? Mention the types with

Examples 3 Marks

These are the standard electrodes with reference to these, the electrodepotentials of any other electrode can be determined.

The Reference Electrodes can be classified in to two typesi) Primary reference electrodes Ex: Standard hydrogen electrodeii) Secondary reference electrodes Ex: Calomel and Ag/Agcl electrodes2.13 Explain the construction, working and limitations of standardhydrogen electrode 6 Marks

The standard hydrogen electrode consists of platinised platinum foilfused to the glass tube. Mercury is placed at the bottom of the tube and


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a copper wire is used for electrical connections. The platinum foil isimmersed in a solution containing unit molar hydrogen ions. Purehydrogen gas is bubbled about the electrode through the H2gas inlet at1atm pressure.The electrode is represented as Pt/H2(g)/H+

If the concentration of H+ is 1M, H2gas bubbled at 1atm pressure and attemperature 298k, then the electrode is called standard hydrogenelectrode. And the electrode potential is arbitrarily fixed as zero.The electrode reactions is

Limitations of SHEi) The construction of SHE is difficult.ii) It is very difficult to maintain the concentration of H+ as 1M and

pressure H2gas at 1atm

iii)

Platinum electrode is poisoned by the impurities of the gasiv) It can not be used in the presence of oxidizing agents.

2.13 Explain the construction and working of Calomel electrode

6 Marks

Calomel electrode consisting of a glass container at the bottom ofwhich mercury is placed above which a layer of mercury and mercurous

chloride (called calomel) is placed with 3/4th

of bottle is filled withsaturated KCl solution. Electrode potential of the cell depends on theconcentration of KCl used. The calomel electrode can be represented as.Hg (l) / Hg2Cl2(S) / Saturated KCl.


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The calomel electrode acts as both anode and cathode dependingupon the other electrode used. The platinum wire is used for electricalconnections. Salt bridge is used to couple with other half cell.

When it acts as anode the electrode reactions is,

Hg2Cl2+ 2e- 2Hg + 2Cl-

When it acts as cathode the electrode reaction isHg2Cl2+ 2e- 2Hg + 2Cl-

Advantages of Calomel Electrode: It is simple to construct.

The electrode potential is reproducible and stable.

It is used as a reference electrode.

2.13. Explain the construction and working of Silver-Silver chlorideelectrode.

6 MarksAg/AgCl electrode is a metal metal salt electrode. It consists of

narrow glass tube at the bottom of which agar is placed above whichsaturated solution of KCl is placed. The silver wire is used for electricalconnections and it is coated electrolytically with AgCl. The cell can berepresented as.Ag(s) / AgCl (s) / Saturated KCl.Electrode acts as both anode and cathode depending on the otherelectrode used. When it acts as anode the electrode reaction is

Ag + Cl- Ag Cl + e-

When it acts as cathode the electrode reaction isAgCl + e- Ag + Cl-.


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2.14. What are Ion Selective Electrodes? Explain the Glass electrode6 MarksThese are the electrodes, which responds to specific ions only and

develops a potential against that ions while ignoring the other ionspresent in the solution.Ex:Glass electrode.

Glass electrode is a pH sensitive electrode widely used for pHdeterminations. It is consisting of a long glass tube at the bottom of


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which a thin and delicate glass bulb, which made up of special type ofglass (12 % Ba2O, 6% of Cao, 72% of SiO2) with low melting point andhigh electrical conductance is used. The glass bulb is filled with 0.1.MHcl and Ag Agcl is used as a internal reference electrode. A platinumwire is used for electrical contant. The glass electrode can be represented

as Ag/AgCl(s) /0.1M (HCl) / Glass.

2.15 Explain the determination of PH using glass electrode.6 Marks

To determine pH of unknown solution the glass electrode iscombined with secondary reference electrode such as calomel electrodeand the glass - calomel electrode assembly is dipped in the solutionwhose pH is to be determined. The two electrodes are connected topotentiometer or pH meter.

The combined electrodes can be represented as.

Hg(l) / Hg2 Cl2 (S) / Saturated KCl //solution of unknown pH/glass/0.1M Hcl/Ag/AgCl(s)

The emf of the above cell is given byE cell= E cathode E anodeE cell= E calomel E glassE glass= E calomel E cellThe potential of E glass is given byE glass= - RT/nf ln [a2/a1]

= RT/nf ln [a1/ a2]


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Where a1 = Concentration of [H+] ions in glass bulba2= Concentration of [H+] ions in unknown solution

E glass= RT/nf ln a1 RT/nf ln [a2]E glass= Constant RT/nf ln [a2]

(Because an [H+] ion in glass bulb is constant)E glass= Constant 0.0591 log [H+]E glass= Constant + 0.0591pHpH = E glass Constant

0.0591pH = E calomel E cell - Constant

0.0591

pH = 0.242 E cell- Constant0.0591

Objective type questions:

1. _____ Converts chemical energy into electricala) Galvanic cell b) Daniel cell c) Dry cell d) all

2. In the anodic chamber ----------- reaction takes placea) Oxidation b) Reduction c) Addition d) Substitution

3. In the cathodic chamber ----------- reaction takes placea) Oxidation b) Reduction c) Addition d) Substitution

4. Origin of electrode potential is explained in

a) Nernst theory b) Helmholtz double layer theoryc) galvanic theory d) Electrochemical theory

5. In two half cells, the one which is having high negative value acts asa) anode b) Cathode c) Dry cell d) None

6. EMF of a concentration cell depends ona) [M1] & [M2] b) No. of charges c) temperature d) All of the above

7. Calomel electrode potential is dependent ofa) Cl-concentration b) Hg2Cl2 c) Temperature d) None

8. Glass electrode is an example fora) Reference electrode b) Ion selective electrodec) Primary electrode d) None

9. Standard electrode potential is nothing but single electrode potential ata) Unit concentration b) 1 atm. pressure c) 298 K d) All of the above


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10. Potential of standard hydrogen electrode is taken asa) 1V b) 0 V c) 10 V d) None

11) Metal rod dipped in a solution of its ion. Its electrode potential is

independent ofa) Temperature of the solution b) Conc. Of the solutionc) Area of the metal exposed d) Nature of the metal

12. Double vertical line (||) representsa) Solid liquid interphase b) Salt bridgec) solid - solid or Liquid - liquid interphase d) None

13. In the pH determination of a solution---------- electrode is used along

with glass electrodea) Ag-Agcl electrode b) Calomel electrodec) Ion selective electrode d) None.

14. A chemical change that occurs when electric current is passedthrough an electrolyte is

a) Conduction b) Dissociation c) Ionization d) Electrolysis

15. Daniel cell is a combination of standard electrodes ofa) Cu & Ag b) Zn & Cd c) Zn & Cu d) Cu & Cd


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REVIEW QUESTIONS

1. What is an electrochemical cell? Explain the types with examples.2. What are galvanic cells? Explain with example3. Mention the cell notations and conventions4. Define single electrode Potential. Explain the origin of electrode

Potential5. Explain the measurement of electrode potential6. Define electron motive force. (EMF)7. Define standard electrode potential. Derive the Nernst equation for

single electrode potential.

8. What are Concentration of cells? Explain with an example.9. What are Reference Electrodes? Mention the types with examples.10. Explain Calomel electrode. Mention its advantages.11. Explain Silver-Silver chloride electrode12. What are Ion Selective Electrodes? Explain the Glass electrode13. Explain the determination of PH using glass electrode.


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U N I TU N I TU N I TU N I T III IIIIIIIII

CONVERTION AND STORAGE OF ELECTROCHEMICALENERGY

BATTERY TECHNOLOGY

3.1 What is a Battery? Explain the classification with examples.6 Marks

Battery is a collection of cells connected either in series or inparallel to get required amount of energy.

Classification of BatteriesBatteries are classified into three types as follows.

a) Primaryb) Secondaryc) Reserved.

a) Primary Batteries:These are the batteries which serve as a source ofenergy only as long as the active chemical species are present in thebattery or in the cell. The cell reactions are irreversible. These aredesigned for only single discharge and cannot be charged again.

Ex: Dry Cell, Zn Hgo cell, Zn-Ag2o cell etc.,

b) Secondary Batteries:These batteries are chargeable and can be usedagain and again. The cell reactions are reversible and are often calledreversible batteries. During discharging the cell acts like voltaic cellconverting chemical energy into electrical energy. During charging thecell acts like electrolytic cell by converting electric energy into chemicalenergy, hence these batteries are called as storage battery.

Ex:Lead acid Battery, Ni-cd battery etc.

c) Reserved Batteries:The batteries which can be stored in an active

state and made ready for use by activating them prior to theapplications (usage) are called as reserved batteries. The keycomponents of the batteries such as electrolyte etc., is separated fromthe battery. And the battery is stored for a longer time. The electrolyteif filled before its usage. The advantages of the reserved batteries are,


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Batteries can be stored for a longer period. To prevent corrosion at contact points during storage. Self-discharging reactions during storage can be eliminated or avoided. They can be used whenever they are required.

Ex: Mg water activated batteries (Mg- Agcl & Mg cucl), Zn-Ag2OBatteries etc.

What are Super capacitors?An Electric double-layer capacitor, also known as supercapacitor,supercondenser, pseudocapacitor, electrochemical double layer capacitor(EDLC), or ultracapacitor, is an electrochemical capacitor that has anunusually high energy density when compared to common capacitors.

3.2 Explain the Characteristics of a battery.

8 MarksA good battery must have the following characteristics.

a) Voltage: The voltage of a battery depends on the energy change in theoverall cell reaction and the nature of cell reaction. To obtain maximumvoltage from a cell.

i) The potential difference between the electrodes must be high.ii) The resistance of the cell must be low.iii) Electrode reactions must be fast to reduce the over potential.

b) Capacity (C): The capacity of a battery is the charge or the amount of

electric current that can be obtained from a battery. It is charge inampere hours (Ah). The capacity of a battery depends oni) Size of a batteryii) Discharge conditions

The capacity of a battery is to be determined by

Where,

C Capacity of battery (in Ah)W Weight of the active materialn number of electrons.F Faradays constant.M Molar mass.


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c) Energy density:Energy density is the ratio of energy available from abattery to its weight or volume

Energy density = Energy available from a batteryWeight or volume of cell.

d)Power density: It is the ratio of power available from a battery to itsweight or volume during discharge power density decreases.

Power density = Power available from a cellWeight or volume of cell.

e) Energy efficiency: The battery should have high-energy efficiency.The percent energy efficiency can be calculated as.

Percentage of Energy efficiency = Energy released on discharge X 100Energy required for charging.

f) Cycle Life: Primary batteries are designed for single discharge andsecondary batteries can be chargeable again and again. The number ofcharge and discharge cycles that are possible in secondary batteries,before failure occurs is called cycle life. The cycle life of batteries must behigh. The factors which decrease the cycle life are:

a) Corrosion at the contact point.b) Leakage of the current.c) Shortening between electrode due to irregular crystal growth and

change in morphologyd) Shedding of the active material from the battery.

g) Shelf life:The duration of storage under specified conditions at theend of which a cell or a battery retains its ability to work or to produceenergy is called shelf life. A good battery should have more shelf life. Itdepends on self-discharge reactions and corrosion at contact points.

3.3Explain the construction and working of Lead acid battery.Mention the electrode reactions and advantages

6 MarksLead acid battery consisting of two flat grids of spongy lead filled withlead (Pb) and lead oxide (PbO2), which acts as anode and cathode

respectively. Several such anode and cathode pairs are immersed in 5 Mor 37% H2SO4of specific gravity 1.25 g/cm3

The battery is encased in plastic or glass container. Each pair of anodeand cathode produces a voltage of 2v.


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Due to the formation of water in the cell reactions during discharging theacid gets diluted when its specific gravity falls below 1.25 g/cm3 thebattery needs charging.

During charging lead and lead oxide is again deposited on anode andcathode respectively and charging reaction is.

Applications:1) Lad acid battery is used for starting motors2) Used in UPS Systems and research centers etc.3) Used in marketing areas etc.4) Used in security and alarm systems.

3.4Explain the construction and working of Nickel-CadmiumBattery. Mention the electrode reactions and advantages

6 MarksNi-Cd Battery consisting of anode and cathode compartments. The Anodecompartments consisting of 78% cadmium, 18% Iron, 1% Nickel andcathode compartment consisting of 80% of Nickel oxy hydroxide, 18% ofgraphite & traces of Barium and cobalt. 6MKOH is used as electrolyte.


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The graphite increases the conductivity, Barium, and cobalt compoundincreases the efficiency of the active materials and cycle life.

Applications:1) Used in electronic devices such as earphones, security and alarm

systems.2) Used in pocket calculators, emergency lights.

3.5 Explain the construction and working of Zinc -air battery.6 Marks

Zinc air battery consisting of anode containing granules of zincmixed with 20%NaOH electrolyte. Cathode can contains a porouscarbon plate which provides site for the reduction reaction and do notinvolves in the reaction. Carbon is catalytically activated to absorboxygen gas. The anode and cathode compartments are separated by aseparator and both are encased in plastic or ebonite insulator. Thereactions are as follows.


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Advantages:i) High energy density.ii) Low cost and compactiii) Does not produce harmful products.

Applications: Used in Military radio receivers, transmitters, hearingaids.

3.6 Explain the construction and working of Nickel - metal hydridebattery.

6 Marks

Nickel Metal hydride battery is made up of anode containing metalhydride such as ZrH2, VH2 and TiH2with hydrogen storage metal alloysuch as La Ni5 or TiNi.Cathode consisting of nickel oxy hydroxide boththe compartments are separated by polypropylene. KOH used aselectrolyte. Cell reactions are as follows.

Applications: Used in electric vehicles, laptops, cellular phones etc.

Advantages: i) Resistance to chemical oxidationii) High energy storage capacity.


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3.7 What are Lithium cells? Explain the construction and workingof Lithium cells? Mention the advantages

Lithium cells 3 MarksLithium cells are most popularly used cells, which are available in

various configurations such as button type, bobbin type, spiral woundprescematic, rectangle etc configuration. The cells have the followingadvantages.

These are light in weight. High energy density More cycle life.

Ex:Li MnO2 cell

Li MnO2 cell 6 Marks

Lithium manganese dioxide cell consisting of anode can containinglithium and the cathode can consisting of specially heat-treatedmanganese dioxide (MnO2). Both anode and cathode are seperated by a

separator made up of polypropylene impregnated with theelectrolyte.(metal salt such as LiCl, LiBr, LiAlCl4which are mixed in aorganic solvent such as 1,2 dimethoxy ethane, and propylene carbonate.)The cell delivers an emf of 3V. The cell reactions are as follows:-

During the all reactions Mn IV stage reduced to Mn III stage.Uses: Li MnO2 cells are used in Safety and Security Devices, Calculator,

watches, automatic camera, memory batteries, cellular phones etc.,

3.8 What are Fuel Cells? Explain the Classification of Fuel cellsbased on temperature

5 Marks


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Fuel cells are the galvanic cells in which chemical energy of fuel isdirectly converted into electrical energy.

Classification of Fuel cells

These are classified into three types as follows.1] Low temp fuel cells: Which operates at the temp range about 75o C

and contains water base electrolytes.

2] Moderate temp fuel cells: Which operates at the temp range about600o C and contains salt electrolyte.

3) High temp fuel cells:Which operates at the temp range about 1000o Cand contains ceramics as electrolyte.

Difference between battery and fuel cellBattery Fuel cell1. A battery stores the chemicalreactants, usually metalcompounds once used up youmust recharge or throw awaythe battery

1.A fuel cell createselectricity throughreactants storedexternally

3.9 Explain the construction and working of H2 O2fuel cell.6 Marks


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Hydrogen - oxygen fuel cells consisting of two porous graphiteelectrodes, which is impregnated with an electro catalyst such as finely,divided Pt Co - Ru or Pt-Ni-Ru. Concentrated KOH is used as anelectrolyte. A wick is placed to maintain water balance. Hydrogen gasand oxygen gas are continuously supplied to the anode and cathoderespectively. The hydrogen undergoes combustion generating electriccurrent. The cell delivers an emf of 1.23v. The cell reactions are asfollows.

Uses: The H2-O2 cells are used in Space vehicles, military and mobilepower systems.

3.10 Explain the construction and working of Methanol Oxygenfuel cell.


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6 Marks

It consists of two electrodes made up of platinum in between theelectrodes H2SO4 is placed as a electrolyte. Methanol and H2SO4 issupplied at the anode and pure oxygen gas is supplied at the cathode.The ethanol is oxidized to CO2 & H2O with the liberation of electricalenergy. The cell delivers an emf of 1.20v. The cell reactions are asfollows.

Uses:1) Used in Military applications.2) Used for large scale power production stations.

3.11 Explain the Classification of fuel cells based on the electrolyte6 Marks

Fuel cells are classified into the following types based on the type ofelectrolyte used.1)Alkaline fuel cells.2) Phosphoric acid fuel cell.3) Molten carbonate fuel cell.4) Solid oxide fuel cell.5) Solid polymer electrolyte fuel cell.


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1)Alkaline fuel cells: These fuel cells containing alkali such as KOH orNaOH as electrolyte. Hydrogen is used as fuel and oxygen gas is usedas an oxidant. The cell operates at a temp of 800C.

Uses: These are used in emergency lights and portable powergenerations, space applications, military applications etc.,

2) Phosphoric acid fuel cells: These fuels cells consisting of 98%phosphoric acid, 2% water as electrolyte, O2 is used as oxidant.Hydrogen LPG, NPG etc are used as fuels. These operate at a temp190 to 200 OC . Platinum alloys such as platinum- cobalt- chromium,are used as electro catalyst.

Uses:These cells are used to provide light and heat in large buildings.

3) Molten carbonate fuel cells: These fuel cells consisting of moltencarbonates such as lithium carbonate 26.2% and potassiumcarbonate (K2CO3) 23% and lithium. Aluminum carbonate as

electrolyte. The anode is made up of nickel and cathode made up ofnickel oxide. Operating temperature is 6500C.

Uses:These are used in chemical industries such as aluminumCloroalkali industries.

4) Solid oxide fuel cells: These contains ZrO2, Y2O3 are solidelectrolytes. Cathode is made up of porous strontium doped withLaMnO3 or In2O3 and SnO2. Anode is made up of cobalt, nickel, orZrO2.Operating temperature is 1000 0C.

Uses:These cells are used in KW power plants, water heating etc,

5) Solid Polymer Electrolyte: These contain ion exchange membraneas solid electrolyte for ionic conduction nafionR membranes whichare chemically and electrochemically stable at 2000C are used.Operating temperature of the cell is 800C. The electrodes are madeup of platinum and noble metals are used as electro catalysts.

Uses: Used in the manned Gemini terrestrial orbital missions.

Objective questions:01. Battery is a

a) Collection of cells connected in series b) Collection of cellsconnected in parallel c) Both a & b d) none

02. Which of the following is a primary batterya) Li-MnO2battery b) Lead acid battery c) Nicd battery d) None

03. Which of the following is a secondary battery


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a) Zn-MnO2 battery b) Li-MnO2 batteryc) Lead acid battery d) Zn-HgO battery

04. In which battery a key component is separated from the rest of thebattery prior to activation.

a) primary battery b) Secondary batteryc) Reserve battery d) None

05. The reaction the takes place at anode of the battery isa) Reduction b) Oxidation c) Neutralization d) Addition

06. Voltage of a battery can be expressed asa) Ohms b) Volts c) Both a & b d) None

07. The electrolyte used in the lead acid battery isa) KOH b) NaOH c) HCl d) H2SO4

08.The electrolyte used in the Zinc air battery isa) KOH b) NaOH c) HCl d) H2SO4

09.The electrolyte used in the Ni-MH battery isa) KOH b) NaOH c) HCl d) H2SO4

10.The electrolyte used in the Li-MNO2battery isa) KOH b) NaOH c) HCl d) LiCl

11. In Ni-MH battery the anode is

a) Ni b) Cd c) ZrH2 d) All

12. In Li-ion battery the anode isa) Ni b) Cd c) ZrH2 d) Li

13. The electrolyte used in alkaline fuel cellsa) NaOH b) H3PO4 c) K2CO3 d) ZrO2

14.The electrolyte used in Phosphoric acid fuel cellsa) NaOH b) H3PO4 c) K2CO3 d) ZrO2

15. The electrolyte used in Molten carbonet fuel cellsa) NaOH b) H3PO4 c) K2CO3 d) ZrO2


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REVIEW QUESTIONS

1 What is a Battery? Explain the classification of Batteries with examples2. Explain any 4 characteristics of a battery.

3. Explain the construction and working of Lead acid battery.Mention the electrode reactions and advantages

4. Explain the construction and working of Nickel-CadmiumBattery. Mention the electrode reactions and advantages

5. Explain the construction, working and application of Zinc -air battery.6. Explain the construction, working and application of Nickel metal

hydride battery.7. What are lithium cells? Explain the construction, working and

application of lithium cell.8. What are Fuel Cells? Explain the classification of fuel cells based on

temperature.9. Describe the construction and working of H2 O2fuel cell.10. Describe the construction and working of methanol Oxygen fuel

cell.11. Explain the classification of fuel cells based on the electrolyte used.


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U N I TU N I TU N I TU N I T IVIVIVIV

CORROSION SCIENCE

4.1 Define corrosion2Marks

Corrosion is defined as the destruction or deterioration of a metalor its alloy and consequent loss of metal, caused due to direct chemicalaction or electrochemical reactions with its environment.

4.2 Explain the electrochemical theory of corrosion6 Marks

According to electrochemical theory, corrosion of metals occursdue to the following changes, when they are exposed to the environment.1) A large number of minute galvanic cells are formed which acts as

anodic and cathodic areas.2) At anode the metal undergoes oxidation and electrons are liberated

which migrates towards cathodic region3) Oxygen of the atmosphere undergoes reduction at cathodic area in the

presence of moisture forming hydroxyl ions at the cathode

Anodic reactions: At anode the metal undergoes oxidation-liberatingelectrons

M Mn+ + ne-

Metal Metal ions

Ex: when iron is exposed to the environment it undergoes

oxidation as

Fe Fe2+ + 2e_

Cathodic reactions: The electrons released at anode migrates tothe cathodic area and reduces oxygen to hydroxyl ions.


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The different cathodic reactions are,

a) In acidic medium: In acidic medium and in the absence ofoxygen, hydrogen ions are reduced to hydrogen gas

2H+

+ 2e-

H2

b) In alkaline and in the absence of O2. If the solution is alkalineand in the absence of oxygen the cathodic reaction is,

2 H2O + 2e- 2OH - + H2

c) In neutral and aerated medium: when the solution is neutral andaerated, hydroxyl ions are formed as follows.

2 H2O + O2 + 4e- 4OH-

d) Formation of corrosion product: The hydroxyl ions migratetowards anode and reacts with metal ions (Mn+ions) and forms corrosionproduct. In the case of iron OH- reacts with Fe2+ ions and forms aninsoluble hydrated ferric oxide known as brown rust.

2Fe+++ 4OH - 2Fe (OH) 2

2Fe (OH)2+ O2+ 2H 2O 2 (Fe 2O 3. 3H 2O) rust.

4.3What is Galvanic series ?The arrangement of elements in the order of their standard reduction

potential is reffered to as emf or electrochemical series. Such aarrangement of few elements given in the table.

Mn+/ M E0(v) Mn+/ M E0(v)Li+/Li -3.05 Cd2+/Cd -0.40K+/K -2.93 Sn2+/Sn -0.14Ba2+/Ba -2.90 Pb2+/Pb -0.13Ca2+/Ca -2.87 H+/H2 0.00Na+/Na -2.71 Cu2+/Cu 0.34Mg2+/Mg -2.37 Ag+/Ag 0.80Al3+/Al -1.66 Hg2+/Hg 0.85

Zn2+/Zn -0.76 Pt2+/Pt 1.20Fe2+/Fe -0.44 Au3+/Au 1.38

1)A negative value indicates oxidation tendency and a positive valueindicates reduction tendency with respect to hydrogen.

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