Experiment1330April2019

DeterminationoftheStandardReductionPotentialofCu2+

Todaywewillmakecopper

usingzinc.

Howwillthatwork?Willwebeusingasupernova?

Ithinkhemeanttosay“makingCubyreducingCu2+withzinc”.Gotit.

Overview:1.  Backgroundinformation2.  Makingthesolutions3.  Makingthegraph4.  Procedure:Whatwearedoing.5.  Yourlabreport

Cu2+(aq)+2e-àCu(s)Eo=?

222

Objective:Todeterminethestandardreductionpotential,Eo,forCu2+(aq)

WewilldetermineEoforthishalf-reaction.

Andweshallseehowwecoulddothesameforanyhalfreaction.Thereis

nothingspecialaboutcopper.

Thisisyourbasiccopper-coloredtulip

Whenweuseditintheureaexperiment,weutilizedthe

factthatΔG=0atequilibrium,sotheequation

becomes:0=ΔGo

sol’n+RTln(Kc)

ΔGsol’n=ΔGosol’n+RTln(Qc)

SeeSection17.10inourbook.

WestartwiththeΔGandQcequationwelearnedaboutinthethermochapter.TheformulaisusedtocalculateΔGunder

non-standardconditions.

InfoforIntroduction 333

1.Backgroundinformation

Weuseditpreviouslyintheureaexperiment.

TheserelationshipsbetweenΔGandEand

ΔGoandEoaresubstitutedin:

ΔG=ΔGo+RTln(Qc)

ΔGo=-nFEo

ΔG=-nFE

E=Eo-ln(Qc)RTnF

-nFE=-nFEo+RTln(Qc)

Followthemath!

E=Eo-log(Qc)2.303RTnFInfofor

Introduction 444

1.Backgroundinformation

1.Backgroundinformation

y=mx+b

Eoisb.That’swhatwearetryingto

determinetoday.

E=Eo-log(Qc)2.303RTnF

y

x

mb

ThisexperimentletsusdetermineEobyusingtheequationofastraightline,

y=mx+b.

InfoforIntroduction 555

1.Backgroundinformation

1.Backgroundinformation

y=mx+b

E=Eo-log(Qc)2.303RTnF

E

log(Qc)

mEo

Butfirst,whynotaddafewmoresimpleconnectorlines…

SoifwegraphEvs.log(QC),wewillknowEo!

InfoforIntroduction 666

1.Backgroundinformation

Obviously.

1.Backgroundinformation

[Zn2+]

Bydesignforthisexperiment,[Zn2+]=0.10M–andnever

changes,so…

Cathode:Cu2++2e-àCuAnode:ZnàZn2++2e-

Cu2++ZnàCu+Zn2+Qc=[Cu2+]

0.10[Cu2+]Qc=

Overall:Cu2++ZnàCu+Zn2+

777

1.Backgroundinformation

Inourexperiment,westudythereductionofCu+2byzinc.

Zincisgray,sothisisazinc-coloredtulip.

1.Backgroundinformation

0.10Cu2++ZnàCu+Zn2+Qc=[Cu2+]

E=Eo-log()2.303RTnF

0.10[Cu2+]

E

log()

mEo

0.10[Cu2+]

WeneedtomakeabunchofsolutionswithvaryingconcentrationsofCu2+sowecanhaveavarietyofvalues

alongthex-axis.ForeachwewillmeasureEandthatshouldmakea

plotlikethisone. 888

2.Makingthesolutions

Great.Let’sgetstarted!I’ll

bringthetulips!

E

log()

mEo

0.10[Cu2+]

Stockfirstsecondthirdfourth

ThestockCu2+solutionisabout0.10M–usetheexactconcentration

provided.Eachdilutioncontains20.0mLoftheprevioussolutionand

30.0mLwater.

Progressivedilutions…

999

2.Makingthesolutions

Stockfirstsecondthirdfourth

SetupyourExcel

spreadsheet

*Stocksolutionconcentrationwillvary.

Progressivedilutions…

*Remember,youcancopyandpaste

formulas.

101010

3.Makingthechart

Startwiththemostdilutesolution.MeasureEforthe4thsolutionfirst,thenthe3rd,thenthe2nd,andthe1st,andlastlyfortheundilutedsolution.

Dofirst

111111

3.Makingthechart

Makeallfivesolutionsbefore

measuringanyEvalues.

121212

3.Makingthechart

log()

Graphthestuffinthebox.Thex-axisis

log(0.10/[Cu2+])andthey-axisisE.

Addthetrendline,displaytheformulaandR2.ThisexamplehasanexcellentR2value,0.995–thecloserto1.00,the

better.

Andthey-interceptisEo=1.086V

131313

3.Makingthechart

Theliteraturevalueis1.10V

log()

141414

4.Whatwearedoingtoday

①  Wearyoursafetyglasses.

②  Thecoversheetsummarizeseverythingthatyouneedtoincludewithyourreport.

③  Wewillfollowtheprocedureprettycloselytoday.Intheanalysispart,wedoprinttheExceldataandchart.

④  Taketimewritinganintroductioninyourownwordsbeforelab.

⑤  Recordobservationsanddetailsascarefullyaspossible.⑥  YoucanrecorddatadirectlyintoExceloryoucancopythedatainto

yourlabnotebook.AttachyourExceldataandgraph

⑦  SetthevoltmetertoreadDCVolts.

⑧  Redwirealwaysgoestothecopperwire⑨  Valuesjumparoundabit.Takeareadingafter10secondsorso.

⑩  Inyourconclusions,calculatepercenterrorfromtheliteraturevalue,Eo=1.10V.

ChemLabwiththeStickPeopleandBirdwascreatedandproducedbyDr.BruceMattson,CreightonChemistry.Enjoyitandshareitifyouwish.

Outearly!Woo-hoo!

151515

5.Yourlabreport

①  First,thecoverpagewithTAinitials.②  Next,thetrimmedcopypagesfromyourlabnotebook③  Next,attachyourNernstchart,includingthedata.④  Stapleeverythingtogether.⑤   Thereisnoon-linecomponentthisweek.⑥  Turninlabreporttodayorbeforethestartofclass

tomorrow.Latelabsmaynotbegraded–seethesyllabus.

StickpeopleinspiredbyxkcdcartoonsbyRandallMunroe

(www.xkcd.com)