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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LESSON8:EquilibriumandAcidReactionsHSCCHEMISTRY

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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.


0

0.15

Change

+𝑥

+2𝑥

Equilibrium

𝑥

0.15 + 2𝑥

- SinceBaF2isonlyslightlysoluble,youmightexpect"2x"tobenegligiblecomparedto0.15.TakethisintoconsiderationandadjustyourICEtable.


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,


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:


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.



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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



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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



23

• 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

lesson 8 (new)- equilibrium and acid reactions - teachersv2€¦ · hsc chemistry module 1:...

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