Electrochemical cell
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An electrochemical cell uses chemical reactions to generate electrical energy. A lemon battery is similar to the first battery invented in 1800 and uses lemon juice as an electrolyte between zinc and copper electrodes. Experiments show that the lemon battery generates electricity through oxidation-reduction reactions, with the voltage decreasing predictably based on factors like the addition of zinc sulfate or changes in acidity. The energy comes from the chemical change that occurs when zinc dissolves in the acid electrolyte.
Electrochemical cell
- 1. Electrochemicalcell Abstract An electrochemicalcell is a device capableofeither derivingelectrical energy from chemical reactionsorfacilitatingchemical reactionsthroughthe introductionof electrical energy.A commonexampleofan electrochemical cell is a standard1.5-volt "battery".(Actuallya single"Galvaniccell"; a batteryproperly consistsofmultiplecells, connectedin eitherparallel orseries pattern.) The lemonbatteryis similarto thefirst electrical batteryinventedin 1800 by AlessandroVolta,who used brine(salt water)insteadoflemonjuice. The lemon batteryis described in sometextbooksin order toillustratethetypeof chemical reaction(oxidation-reduction)thatoccursin batteries.The zincandcopperare called theelectrodes, andthe juice insidethe lemonis called theelectrolyte.There are many variationsofthelemon cell thatuse different fruits (orliquids) as electrolytesand metalsotherthanzinc andcopper as electrodes. Batteriesareused to illustratethe connectionbetweenchemistry andelectricity as well as to deepen thecircuit concept
- 2. forelectricity. The fact thatdifferent chemicalelements such as copperandzincare used can beplaced in thelargercontext thattheelements do notdisappearorbreak down when they undergo chemicalreactions.Batteriesserve toillustratetheprinciples ofoxidation-reductionreactions. Introduction This modelofthe chemicalreactionsmakes severalpredictionsthat were examinedin experiments published byJerry Goodismanin2001.Goodismannotesthatnumerous recent authorsproposechemical reactionsforthelemon batterythatinvolve dissolutionofthecopper electrode intotheelectrolyte. Goodismanexcludes this reactionas beinginconsistentwiththeexperiments,andnotesthat thecorrect chemistry,which involvesthe evolutionofhydrogen atthe copperelectrode, has been knownfor manyyears.When the electrolytewas modifiedby addingzincsulfate (ZnSO4),thevoltagefrom thecell was reduced as predicted usingtheNernst equation forthe model.The Nernst equationessentiallysayshowmuch thevoltagedrops as morezincsulfateis added.
- 3. The additionof coppersulfate(CuSO4)did notaffect thevoltage.This result is consistent.When thebatteryis hooked up toan externalcircuit anda significant electrical current is flowing, thezincelectrode loses mass,aspredicted by thezinc oxidationreactionabove.Similarly,hydrogen gas evolves as bubbles fromthe copper electrode. Finally,thevoltagefrom the cell depended uponthe acidity ofthe electrolyte, as measuredbyits pH; decreasing acidity (andincreasingpH) causes thevoltageto fall. This effect is also predicted bythe Nernstequation;theparticularacid thatwas used (citric, hydrochloric,sulfuric, etc.) doesn'taffect thevoltageexcept throughthe pH value. Productionofcurrent throughSELFMADEbattery
- 4. The Nernstequationprediction failed forstronglyacidelectrolytes (pH < 3.4),when thezinc electrodedissolves intothe electrolyteeven when the batteryis notproviding anycurrent to a circuit. The two oxidation-reductionreactionslistedaboveonlyoccur when electrical charge can betransportedthroughtheexternalcircuit. The additional,
- 5. open-circuitreactioncan be observedby theformationofbubbles at thezincelectrode under open-circuit.This effect ultimatelylimited thevoltageof thecells to 1.0 Vnear roomtemperatureat thehighest levels of acidity. Energysource The energycomes from thechemical changein thezinc (orothermetal)when it dissolves intotheacid. The energy does notcomefrom thelemon orpotato.Thezincis oxidized inside thelemon,exchangingsomeofits electronswith theacid in order to reach a lowerenergystate,andtheenergy releasedprovides the power. In current practice, zincis produced by electronwinningofZnSO4orpyrometallurgicreduction ofzinc withcarbon,which requires anenergy input. The energy produced in the lemon batterycomesfrom reversingthis reaction,recoveringsomeoftheenergy inputduring thezinc production. MaterialRequired • DistilledWater,Coldrink, SaltWater
- 6. • ConnectingWire • CopperAndZinc Strips • DigitalClock Procedure • Assemblea “connectionpair”by connectingthewire carefully threadthe wire’s exposed metallicend throughthe holes on theplate.Gently twistwire to secure it to theplate. • Afterwards,connectthe blackwire from theLCD clock (negative)tooneofthe zinc plate.Then connectred wire from LCDclock (positive)to piece ofcopper plate.Nowall thecomponentsareconnected • Insertthecopper andzincplates intosaltwatersuch thatthe metallicstripsdo not toucheach other.The clock nowstartstowork. • Repeatthis experiment with distilled water& coldrink.
- 7. Observation As soonaswe connectthe wires andput thekey on electricity generatedby the fruit juice flows throughtheclock, makingthe clock run in caseof saltwaterandcoldrink. The clock does notwork when the rods areimmersedin distilled wateras no current flows. Result/Conclusion The metalstrips andliquid makea simple batterythatcreates theelectricity to operate theclock. Saltywaterandcoldrinkwork as a device called electrochemicalcell. It convertsthechemical energystoredin themetalstripsinto stripsintoelectrical energy. A cell works because ofthechemical properties ofthemetals inside(in this casethe copperandzinc). The different properties causetiny particles charged withelectricity (ions)tomovebetween thetwo stripsof metal.This flow is an electric current.The liquid which conduct electricitycontainstheparticles thatallowthecurrent to flow,
- 8. but it stopsthe metalstouching.Electric current alsoflows alongthewire between the zincandcopper strips& the clock. This current makes the clock run. SALTWATER:Theionspresent in commonsaltsodium chloride dissociateinto ionsof sodium andchloride. These ionsare responsibleforconductionofelectricity. Potential is providedby copper andzincrods. DISTILLEDWATER:Thereis absenceofionsin distilled waterthereforethedistilled waterdoesn'tconduct electricityandhence theclock doesn’t work.Though theH+ and OH- but thepH is 7 thereforethe ion dissociationisnotenoughonly 10-7MH+ is present in distilled water.so this can notconduct electricity. COLDRINK:Thecoldrinktoocontainsionswhich dissociatetoconduct electricity