Lesson 8 (new)- Equilibrium and Acid Reactions - teachersV2€¦ · HSC Chemistry Module 1:...
Transcript of Lesson 8 (new)- Equilibrium and Acid Reactions - teachersV2€¦ · HSC Chemistry Module 1:...
HSC Chemistry
Module 1: Equilibrium and Acid Reactions Lesson8:TheCommonIonEffect
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SummaryofKeywords
AccountAccountfor:statereasonsfor,reporton.Giveanaccountof:narrateaseriesofeventsortransactions
AnalyseIdentifycomponentsandtherelationshipbetweenthem;drawoutandrelateimplications
ApplyUse,utilise,employinaparticularsituation
AssessMakeajudgementofvalue,quality,outcomes,resultsorsize
CalculateAscertain/determinefromgivenfacts,figuresorinformation
ClarifyMakeclearorplain
ClassifyArrangeorincludeinclasses/categories
CompareShowhowthingsaresimilarordifferent
ConstructMake;build;puttogetheritemsorarguments
ContrastShowhowthingsaredifferentoropposite
DeduceDrawconclusions
DefineStatemeaningandidentifyessentialqualities
DemonstrateShowbyexample
DescribeProvidecharacteristicsandfeatures
DiscussIdentifyissuesandprovidepointsforand/oragainst
DistinguishRecogniseornote/indicateasbeingdistinctordifferentfrom;tonotedifferencesbetween
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EvaluateMakeajudgementbasedoncriteria;determinethevalueof
ExamineInquireinto
ExplainRelatecauseandeffect;maketherelationshipsbetweenthingsevident;providewhyand/orhow
ExtractChooserelevantand/orappropriatedetails
ExtrapolateInferfromwhatisknown
IdentifyRecogniseandname
InterpretDrawmeaningfrom
InvestigatePlan,inquireintoanddrawconclusionsabout
JustifySupportanargumentorconclusion
OutlineSketchingeneralterms;indicatethemainfeaturesof
PredictSuggestwhatmayhappenbasedonavailableinformation
ProposePutforward(forexampleapointofview,idea,argument,suggestion)forconsiderationoraction
RecallPresentrememberedideas,factsorexperiences
RecommendProvidereasonsinfavour
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LessonDotpointsInquiryquestion:Howcanthepositionofequilibriumbedescribedandwhatdoestheequilibriumconstantrepresent?PredictingtheFormationofaPrecipitate• Predicttheformationofaprecipitategiventhestandardreferencevaluesfor
Ksp
SolubilityEquilibriatoDetoxifyFood• InvestigatetheuseofsolubilityequilibriabyAboriginalandTorresStrait
IslanderPeopleswhenremovingtoxicityfromfoods,forexample:
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1. PredictingtheFormationofaPrecipitate
CHECKPOINT:
IonProduct
• Rememberinlesson3,youalsolearntaboutthereactionquotient,Qwhere,
- IfQ=K,thereactionisatequilibrium- IfQ≠KthereactionisNOTatequilibrium
• 𝑄#$iscalledtheIonProductexpressionforaslightlysolubleioniccompound
• Similarly,theionproduct(𝑄#$)ofasaltistheproductoftheconcentrationsof
theionsinsolutionraisedtothesamepowersasinthesolubilityproductexpression.- Itisanalogoustothereactionquotient(Q)discussedforgaseous
equilibria.
- WhereasKspdescribesequilibriumconcentrations,theionproductdescribesconcentrationsthatarenotnecessarilyequilibriumconcentrations.
• PredicttheformationofaprecipitategiventhestandardreferencevaluesforKsp
IFQ>K• Thereactionfavoursthereactants
IFQ<K• Thereactionfavourstheproducts
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• Foranyslightlysolublecompound,𝑀$𝑋' ,whichconsistsofions𝑀()and𝑋*+thegeneralformulafortheionproductwouldbe:
- Forexample,theionproductofasilverchloridesolutionisrepresentedby:
𝑄#$ = 𝑨𝒈) [𝑪𝒍+]
• Therefore,bycalculating𝑄#$andcomparingitto𝐾#$,youcanpredictwhether
aprecipitatewillformornot
• Whatcanweconcludeabout𝐾#$?
Thesolubilityproductgivesthemaximumvaluesoftheionconcentrationsthatareallowed
• Forexample,asolutionofMagnesiumHydroxideisdissolvedinwaterthe
followingequationcanbewritten:
𝑀𝑔(𝑂𝐻)9 𝑠 → 𝑀𝑔9)(𝑎𝑞) + 2𝑂𝐻+(𝑎𝑞)- If 𝑀𝑔9) 𝑎𝑞 𝑂𝐻+ 𝑎𝑞 9 < 𝐾#$then,
Theconcentrationsarenotyetatequilibrium,thereforemoresolidcandissolve.
- If 𝑀𝑔9) 𝑎𝑞 𝑂𝐻+ 𝑎𝑞 9 > 𝐾#$then,
TheconcentrationsareGREATERthentheequilibrium,thereforeprecipitationmustoccur
𝑄#$ = [𝑀()]$[𝑋*+]'
IF𝑸𝒔𝒑 ≥ 𝑲𝒔𝒑• Thesolutionissaturatedandaprecipitatewillform
IF𝑸𝒔𝒑 < 𝑲𝒔𝒑• ThesolutionisunsaturatedandNOprecipitatewillform
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ExampleCalculation1–Predictingtheformationofprecipitategiven𝐾#$• SupposeasolutionhasCa2+andSO42-concentrationsof0.0052Mand0.0041
M,respectively.Iftheseconcentrationsweredoubledbyevaporatinghalfthewaterinthesolution,wouldprecipitationofCaSO4occurgiventhattheKspforcalciumsulfateis2.4x10-5?
SincetheKspexpressionforcalciumsulfateis
Ksp= 𝐶𝑎9) [𝑆𝑂J9+]theninitially,
Qsp=Ksp= 𝐶𝑎9) [𝑆𝑂J9+]EvaporatinghalfofthewaterwoulddoubletheinitialconcentrationsofCa2+andSO42-to0.0104Mand0.0081M,respectively.SubstitutingtheseinitialconditionsintotheexpressionforQsp,weobtain
Qsp=(0.0104)(0.0082)=8.53x10-5SincethisvalueforQspisgreaterthantheKsp,youwouldexpectprecipitationtooccur.
ExampleCalculation2–PredictingtheformationofprecipitatewhensolutionsaremixedAsolutionof0.00016Mlead(II)nitrate,Pb(NO3)2,waspouredinto456mLof0.00023Msodiumsulfate,Na2SO4.• Writeanequationforthereaction.
𝑃𝑏(𝑁𝑂N)9 𝑎𝑞 + 𝑁𝑎9𝑆𝑂J 𝑎𝑞 → 𝑃𝑏𝑆𝑂J 𝑠 + 2𝑁𝑎𝑁𝑂N(𝑎𝑞)
• Wouldaprecipitateoflead(II)sulfate,PbSO4,beexpectedtoformif255mLof
theleadnitratesolutionwereadded?(TheKspforlead(II)sulfateis1.7x10-8)
- Weneedtocalculatetheconcentrationofionsthatwouldformtheprecipitate.
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- Todothis,weneedtousetheconcentrationsofthesolutionsandthefinalvolumeofthemixturetodeterminetheconcentrationofionsinthemixture.Thereforethefollowingformulaisused:
- Now,findtheconcentrationsof𝑃𝑏9)and𝑆𝑂J9+.
𝑃𝑏9) =𝑐P𝑉P𝑉9
=0.00016𝑚𝑜𝑙/𝐿 0.255𝐿
0.711𝐿 = 5.74×10+_𝑀
𝑆𝑂J9+ =𝑐P𝑉P𝑉9
=0.00023𝑚𝑜𝑙/𝐿 0.456𝐿
0.711𝐿 = 1.48×10+J𝑀
- Calculatetheionproduct,𝑄#$anddeterminewhetherprecipitationoccurs.
𝑄#$ = 𝑃𝑏9) 𝑆𝑂J9+ = 5.74×10+_𝑀 1.48×10+J𝑀 = 8.48×10+b
Since,𝑄#$ < 𝐾#$wewouldnotexpectprecipitationtooccur.
𝒄𝟏𝑽𝟏 = 𝒄𝟐𝑽𝟐
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Applications2.1Question1AsolutionofBa(NO3)2isaddedtoasolutionofNa2SO4.a) Predicttheprecipitateproduced.(1mark)
𝐵𝑎𝑆𝑂J(𝑠)
b) Whichgraphbelowshowstheamountofprecipitatecollectedfromafixed
amountofNa2SO4solutionastheBa(NO3)2isaddedindefinitely?(1mark)
A
Question2Asolutionismadebymixing500.0mLof0.12MNaOHsolutionwith500.0mLof0.10MMg(NO3)2.(Kspis1.8×10-11)a) Assumingthatnoreactionoccurs,whatwill[Mg2+(aq)]and[OH-(aq)]beafter
mixing?(2marks)
[Mg2+(aq)]=0.050Mand[OH-(aq)]=0.060Mb) Writedownthevalueoftheionicproduct,Qsp.(2marks)
c) Doesaprecipitateform?(1mark)
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Question3Foreachofthefollowingexperiments,predictwhetherornotaprecipitateofMgF2willform.
Ksp(MgF2(s))=6.4×10-9a) 500.0mLof0.050MMg(NO3)2ismixedwith500.0mLof0.010MNaF.
(3marks)
b) 500.0mLof0.050MMg(NO3)2ismixedwith500.0mLof0.0010MNaF.
Question4Willaprecipitateof𝐶𝑢(𝑂𝐻)9formwhen10.0mLof0.010MNaOHisaddedto1.00Lof0.010M𝐶𝑢𝐶𝑙9?(𝐾#$ = 2.6×10+Pb)(4marks)Question5Sodiumbromideandleadnitratearesolubleinwater.Willleadbromideprecipitatewhen1.03gofNaBrand0.332gof𝑃𝑏(𝑁𝑂N)9aredissolvedinsufficientwatertogive1.00Lofsolution?(𝐾#$𝑜𝑓𝑃𝑏𝐵𝑟9 = 6.6×10+k)(5marks)Question6Willaprecipitateformif90.0mLof0.200Mtin(II)nitrateisaddedto10.0mLof0.200Msodiumiodide.(Kspfortiniodideis1.0×10+J)(4marks)
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Question7If5.00mLof0.300Mlead(II)nitrateismixedwith10.0mLof0.150Msodiumchloride,aprecipitateof𝑃𝑏𝐶𝑙9.However,if5.00mLof0.0300Mlead(II)nitrateismixedwith10.0mLof0.015Msodiumchloride,noprecipitateforms.ExplaintheseobservationsbycalculatingQforeachreactionandcompareQtoKsp𝑃𝑏𝐶𝑙9.(𝐾#$ = 2.4×10+J)(6marks)
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TheCommonIonEffect• Upuntilthispoint,youhaveonlyexaminedtheequilibriaofsaltsdissolvedin
purewater
• Thecommon-ioneffectisusedtodescribetheeffectonanequilibriuminvolvingasubstancethataddsanionthatisapartoftheequilibrium.
• Intheeventthatwewouldtrytodissolveasaltinasolutionofanothersaltcontainingthesamecationoranion,thiscommonionhasacumulativeeffectonthesolubilityequilibrium.
- Howdoyouthinkacommonionwouldeffectthesolubilityofionic
compounds?Itwouldgreatlydecreasethesolubilityofioniccompounds
LeChatelier’sPrincipleandSolubility
• RememberthataccordingtoLeChatelier’sPrinciple:
- Iftheconcentrationofareactantisincreased,theequilibriumrespondsby
producingmoreproducts
- Iftheconcentrationofaproductisincreased,theequilibriumrespondsbyproducingmorereactant
• Forexample,supposewehaveasolutionof0.10MNaCl.
𝑨𝒈𝑪𝒍 𝒔 ⇌ 𝑨𝒈) 𝒂𝒒 + 𝑪𝒍+ 𝒂𝒒
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- IfsolidAgClisaddedtotheNaClsolutionuseLeChetalier’sPrincipletoexplainthecommonioneffect.
Thecommonionis𝐶𝑙+,sothereforetheadditionof𝐶𝑙+ionswillcausethepositionofequilibriumwillshifttothereactantsside(left).Therefore,thesolubilityofAgClisreducedbythepresentofthecommonion𝐶𝑙+.
• Ifasparinglysolublesaltwasaddedtoasolutionwithacommonion,wecan
assumethat:
ExampleCalculation–CalculatingthesolubilityofaSlightlySolubleSaltinaSolutionofaCommonIona) Calculatethemolarsolubilityofbariumfluoride,BaF2,inwaterat25℃.TheKsp
at25℃is1.0x10-6.
- Theequilibriumforthedissolutionis:
𝑩𝒂𝑭𝟐 𝒔 ⇌ 𝑩𝒂𝟐) 𝒂𝒒 + 𝟐𝑭+ 𝒂𝒒
- Whatratiodothebariumandflourideionsenterthewaterat?
1: 2𝑟𝑎𝑡𝑖𝑜
- Lettheratioberepresentedas𝑥.FillintheICETablebelow
𝑩𝒂𝑭𝟐 𝒔 ⇌ 𝑩𝒂𝟐) 𝒂𝒒 + 𝟐𝑭+(𝒂𝒒)Initial
0
0
Change
+𝑥
+2𝑥
Equilibrium
𝑥
2𝑥
Theconcentrationofthecommonionisentirelyfromtheionsthatarealready
presentinthesolution.
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- Now,calculatethemolarsolubilityofBariumFlouride.Explainwhatyouranswermeans.
𝐾#$ = 𝐵𝑎9) 𝐹+ 91.0×10+k = 𝑥 2𝑥 9
1.0×10+k = 4𝑥N𝑥 = 1.0×10+kw
= 6.30×10+N𝑀
Since"x"representsthemolarityoftheBa2+ion,andwegetonemoleofbariumionsforeachmoleofbariumfluoridethatdissolves,weobtainamolarsolubilityforBaF2of6.30x10-3M.
Now,toillustratethecommonioneffect.b) Whatisthemolarsolubilityofbariumfluorideinasolutionthatis0.15MNaF
at25℃.- Initially,thereareno𝐵𝑎9)ionspresentand0.15MinF-ions.Therefore,
wemustmakeanadditiontoourequilibriumconcentrations.Usetheinformationfroma)fillintheICETablebelow.
𝑩𝒂𝑭𝟐 𝒔 ⇌ 𝑩𝒂𝟐) 𝒂𝒒 + 𝟐𝑭+(𝒂𝒒)Initial
0
0.15
Change
+𝑥
+2𝑥
Equilibrium
𝑥
0.15 + 2𝑥
- SinceBaF2isonlyslightlysoluble,youmightexpect"2x"tobenegligiblecomparedto0.15.TakethisintoconsiderationandadjustyourICEtable.
𝑩𝒂𝑭𝟐 𝒔 ⇌ 𝑩𝒂𝟐) 𝒂𝒒 + 𝟐𝑭+(𝒂𝒒)Initial
0
0.15
Change
+𝑥
0
Equilibrium
𝑥
0.15+0
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- Writetheexpressionfor𝐾#$andcalculatethemolarsolubility.
𝐾#$ = 𝐵𝑎9) 𝐹+ 91.0x10-6= 𝑥 0.15 9
𝑥 = 4.44×10+_𝑀
c) Compareyouranswersfora)andb).Dotheyillustratethecommonioneffect?
Thereforethemolarsolubilityofbariumfluoridein0.15MNaFisonly4.44x10-5M.Inpurewater,thesolubilityis6.3x10-3M.Since𝐹+isthecommonion,thesolubilityofBaF2waslowerinb)thenina).Therefore,demonstratingthecommonioneffect.
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Applications2.2Question1PbCl2isnotverysolubleinwater.Thepictureshowsatesttubecontainingasaturatedsolutionofleadchlorideincontactwithaprecipitateofsolid.
a) Writedownthesolubilityproductexpression,Ksp,forleadchloride.(2marks)
𝑃𝑏𝐶𝑙9 𝑠 → 𝑃𝑏9) + 2𝐶𝑙+
𝐾#$ = 𝑃𝑏9) 𝑎𝑞 𝐶𝑙+ 𝑎𝑞 9
b) SodiumchloridedissolvescompletelytogiveNa+(aq)andCl-(aq)ions.If
sodiumchlorideisaddedtothesaturatedsolution,whatwouldbetheeffectonthesolubilityofleadchloride?(2marks)Adding𝐶𝑙+ionswouldpushtheequilibriuminthedirectionofreactants:thesolubilitywoulddecrease.
c) Ifsodiumchlorideisaddedsothat[Cl-(aq)]=0.5M,rearrangeyourKsp
expressiontogive[Pb2+(aq)].(3marks)With 𝐶𝑙+ 𝑎𝑞 = 0.5𝑀,
𝐾#$ = 𝑃𝑏9) 𝑎𝑞 𝐶𝑙+ 𝑎𝑞 9
𝑃𝑏9) 𝑎𝑞 =𝐾#$
𝐶𝑙+ 𝑎𝑞 9 =𝐾#$0.59 = 4𝐾#$
d) WhatistheeffectofaddingextraPbCl2(s)tothetesttube?(3marks)
AddingextraPbCl2(s)hasnoeffect.Asthe[Pb2+(aq)]and[Cl-(aq)]arealreadysuchthat[Pb2+(aq)][Cl-(aq)]2=Ksp,thesolutionissaturatedanditisnotpossibletodissolvemoresolid.
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Question2Lead(II)Chloridehasa𝐾#$valueof1.70×10+_at25℃.Lead(II)Chlorideismixedwitha0.20mol/LsolutionofNaCl.Thefollowingtableiscreatedtoassistwiththeresult.
PbCl9 s ⇌ Pb9) aq + 2Cl+(aq)Initial Change Equilibrium
CalculatethemolarsolubilityofLead(II)Chlorideandexplainyourworking.(6marks)
𝑁𝑎𝐶𝑙 𝑎𝑞 ⇌ 𝑁𝑎) + 𝐶𝑙+Thecommonionis𝐶𝑙+.Initially,thereareno𝑃𝑏9)ionspresent.However,beforethePbCl9dissolvesthereare0.20mol/Lof𝐶𝑙+insolution.WhenPbCl9 s isaddedtowater,𝑃𝑏9)and𝐶𝑙+ionsenterthesolutionata1:2ratio.Letthisberepresentedby𝑥.Thereforefora1Lsolution:
𝐏𝐛𝐂𝐥𝟐 𝐬 ⇌ 𝐏𝐛𝟐) 𝐚𝐪 + 𝟐𝐂𝐥+(𝐚𝐪)Initial 0 0.20Change +𝑥 +2𝑥
Equilibrium +𝑥 0.20 + 2𝑥SincePbCl9isonlyslightlysoluble,the𝐶𝑙+ionscontributedarenegligibleandhenceitcanbeassumedthatallofthe𝐶𝑙+ionscomefromNaCl.Therefore,thetableisadjusted:
𝐏𝐛𝐂𝐥𝟐 𝐬 ⇌ 𝐏𝐛𝟐) 𝐚𝐪 + 𝟐𝐂𝐥+(𝐚𝐪)Initial 0 0.20Change +𝑥 +0
Equilibrium +𝑥 0.20NowcalculatingthemolarsolubilityofPbCl9:
𝐾#$ = 𝑃𝑏9) 𝑎𝑞 𝐶𝑙+ 𝑎𝑞 9
1.70×10+_ = 𝑥 0.20 9
𝑥 =1.70×10+_
0.20 62 = 4.3×10+J𝑚𝑜𝑙/𝐿
ThemolarsolubilityofPbCl9in0.20mol/LNaClis4.3×10+J𝑚𝑜𝑙/𝐿.
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Question3The𝐾#$forAgClat25℃is1.80×10+P�.a) Whatisthemolarsolubilityofsilverchloridein1.0Lofsolutionthatcontains
2.0×10+9ofHCl?Explainyouranswer.(6marks)
Thecommonionis𝐶𝑙+.Initially,thereareno𝐴𝑔9)ionspresentand0.020mol/Lof𝐶𝑙+𝑓𝑟𝑜𝑚𝐻𝐶𝑙.WhenAgClisaddedtowater,𝐴𝑔)and𝐶𝑙+ionsenterthesolutionata1:1ratio.Letthisberepresentedby𝑥.Thereforefora1Lsolution:
𝐀𝐠𝐂𝐥 𝐬 ⇌ 𝐀𝐠) 𝐚𝐪 + 𝐂𝐥+(𝐚𝐪)
Initial 0 0.020Change +𝑥 +𝑥
Equilibrium +𝑥 0.020 + 𝑥SinceAgClisonlyslightlysoluble,the𝐶𝑙+ionscontributedarenegligibleandhenceitcanbeassumedthatallofthe𝐶𝑙+ionscomefromHCl.Therefore,thetableisadjusted:
𝐀𝐠𝐂𝐥 𝐬 ⇌ 𝐀𝐠) 𝐚𝐪 + 𝐂𝐥+(𝐚𝐪)Initial 0 0.020Change +𝑥 +0
Equilibrium +𝑥 0.020NowcalculatingthemolarsolubilityofPbCl9:
𝐾#$ = 𝐴𝑔) 𝑎𝑞 𝐶𝑙+ 𝑎𝑞
1.80×10+P� = 𝑥 0.020 𝑥 = 9.0×10+b
ThemolarsolubilityofAgClin0.020mol/LHClis9.0×10+b𝑚𝑜𝑙/𝐿.
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b) Comparethemolarsolubilityofsilverchloridein1.0Lofsolutionthatcontains2.0×10+9ofHCltoAgClinwater.(4marks)ForAgClinwater, 𝐀𝐠𝐂𝐥 𝐬 ⇌ 𝐀𝐠) 𝐚𝐪 + 𝐂𝐥+(𝐚𝐪)
Initial 0 0Change +𝑥 +𝑥
Equilibrium +𝑥 +𝑥
𝐾*$ = 𝑥91.8×10+P� = 𝑥9𝑥 = 1.3×10+_𝑚𝑜𝑙/𝐿
1.3×10+_
9.0×10+b = 1444Therefore,thesolubilityisreducedbyafactorofabout1444.
LESSON8:EquilibriumandAcidReactionsHSCCHEMISTRY
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SelectivePrecipitation• Wherethereisapossibilityfortwosaltstoprecipitate,thelesssolublewill
precipitatefirst.ExampleCalculation• 𝐶𝑎𝑆𝑂Jhas𝐾#$ = 2.4×10+_and𝑆𝑟𝑆𝑂J(strontiumsulfate)hasa𝐾#$ =
2.8×10+�.Asolutionhasaconcentrationof0.10MofbothCa2+andSr2+;thenNa2SO4(s)isslowlyadded.
- Possibleprecipitatesinclude𝐶𝑎𝑆𝑂Jand𝑆𝑟𝑆𝑂J.Whichofthetwowill
precipitatefirstSrSO4hasthelowerKspandwillprecipitatefirst
- Whatisthe[𝑆𝑂J9+]atthepointwhereprecipitationstarts?
SincetheKspexpressionforstrontiumsulfateis
Ksp= 𝑆𝑟9) [𝑆𝑂J9+]theninitially,
Qsp=Ksp= 𝑆𝑟9) 𝑆𝑂J9+ 2.8×10+� = 𝑆𝑟9) 𝑆𝑂J9+
= (0.10) 𝑆𝑂J9+
𝑆𝑂J9+ = 9.�×P���
�.P�= 2.8×10+k𝑀,whenprecipitateofSrSO4startstoform
• AsfurtherNa2SO4isadded,the[SO42-]increasesandSrSO4continuesto
precipitate.
• Precipitationdecreasesthe[Sr2+],soasteadyincreasein[SO42-]isnecessaryfortheionproductofSrSO4tobeexceeded
• Eventuallythe[SO42-]willbelargeenoughtoexceedtheionproductforCaSO4anditwillalsostartprecipitating.
- Calculatethe[SO42-]whenCaSO4startstoprecipitate.
Ksp= 𝐶𝑎9) 𝑆𝑂J9+ 2.4×10+_ = (0.10) 𝑆𝑂J9+
𝑆𝑂J9+ = 9.J×P���
�.P�= 2.4×10+J𝑀,whenprecipitateofCaSO4startstoform
LESSON8:EquilibriumandAcidReactionsHSCCHEMISTRY
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- Calculatethe[Sr2+]whenCaSO4startstoprecipitate.
Using 𝑆𝑂J9+ = 2.4×10+J𝑀Ksp=2.8×10+� = 𝑆𝑟9) 𝑆𝑂J9+
= 𝑆𝑟9) (2.4×10+J𝑀)𝑆𝑟9) = 9.�×P���
9.J×P���= 1.2×10+N𝑀,whenprecipitateofCaSO4startstoform
- Whatpercentageof[Sr2+]hasprecipitated?
𝑆𝑟9)𝑟𝑒𝑚𝑎𝑖𝑛𝑖𝑛𝑔 =0.00120.100 = 0.012
Therefore99%ofSr2+hasprecipitated
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2. SolubilityEquilibriatoDetoxifyFood
CHECKPOINT:
Cycad
• Inyear11youlearntaboutthecycadMacrozamiawhichwasexploitedasan
importantfoodsourceinspiteofitsbeinghighlytoxicandcarcinogenic.
• TheAboriginalPeoplehaddevelopedmethodsofremovingthetoxinsthat
allowedthecycadseedstobecomearichfoodsource.
• Differentindigenousgroupshaddifferentmethodsofremovingthetoxins,buttheyallachievedthesandend,anedible,sustaining,fruit.
• Thereweretwomainmethodsofremovingthetoxinsfromthefruit:
Method1–Leeching(SolubilityEquilibria)• Kernelsarecutopen,groundandthetoxinsareleachedoutinwaterasthey
arerelativelysoluble- Whydotheyneedtobeground?
Itincreasesthesurfaceareaallowingthewatertoleachthetoxinsmoreeasily.
• InvestigatetheuseofsolubilityequilibriabyAboriginalandTorresStraitIslanderPeopleswhenremovingtoxicityfromfoods,forexample: - Toxinsincycadfruit
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• Thekernelsarethenfurthergroundintoapowderlikeflowerandbakedtomakecycadbread.
Method2–Fermentation• Kernelsarestoredinalargecontainer,orinsomecasespits,wherethey
remainforseveralmonths
• Theprocessiscompletewhenthekernelshavefrothedorbecomemouldy(fermented)
BitterYam
• BitteryamisafoodeatenbytheTiwiPeopleattheNorthernTerritoryinthe
TiwiIslands
• TheTiwiritualisethedetoxificationoftheyamthroughtheKulamaceremony
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• Leachingisthemainmethodtoremoveanytoxins.Hereistheprocess:
1. YamsarepickedthroughspecificrulessothattherootsareNOTdamaged
2. Theyamsareplacedinrunningwatertomovetheoxalatesthroughleaching
3. Earthovensareprepared,inwhichtheyamsareroasted