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Chemistryinyourcupboard:Finish

Introduction

Machinedishwashingisacomplexprocesswhichhastorelyonchemistryratherthanmanual effort to clean dishes. Dishwasher cleaning products contain a huge range ofchemicals including surfactants or detergents, alkalis, bleaches, biosubstances andbuilders.Eachof thesehasadistinct role in thecleaningofdishesbut thedifficulty isgetting all these working together when they have different optimum conditions.Finish™ is abrandwith a rangeofproducts available indifferent formulationsbut allbasedonthesamebroadprinciples.

Linkstothecurriculum

This section contains information relevant to the following areas of your chemistrycurriculum:

Ratesofreactions Group7elements Group1and2elements Biochemistry(proteins,fatsandcarbohydrates) Acidsandbases

FINISH

AccordingtotheOfficeofNationalStatistics,in2008almost40%ofhomesintheUKhadadishwasher,upfromaround25%in1998.Itistemptingtothinkofmachinedishwashingascomparabletohandwashingofdishesbutinfactitisamuchmorecomplexprocessandinvolvesagreatdealmorechemistry.

Handdishwashingreliesmostlyonmechanicaleffort‐continuingtobrushorsponge(withthehelpofhotwaterandadetergent),untilthedishesappearclean.Withmachinedishwashing,mechanicaleffortcountsforless,andthechemistryhastodothecleaning.However,theconditionsformachinewashingcanbebothhotterandmorealkalinethatcouldbewithstoodbyhumanhands.

Herewewilllookatsomeofthechemistrythatgoesoninsidethedishwasherandrelateittochemistrythatyoualreadyknow.Thescienceofdishwasherproductsiscomplexandwecanonlycoverthebasicshere.

Didyouknow?JosephineCochraneinventedthemoderndishwasherin1886.


Cochranewasawealthysocialitewhoseservantskeptchippingherfinechinawhilehandwashingit.Shedevelopedarackandwaterjetsystemthatwasfirstdemonstratedatthe1893ChicagoWorldFair.

Figure1:AproductfromtheFinishrange

Howdoesadishwasherwork?(1of2)Beforeweconsiderthechemistry,weneedtounderstandthemechanicsofadishwasher,Figure2.Thisisessentiallyverysimple.

Figure2:Thebasiclayoutofadishwasher(courtesyofhowstuffworks.com)


Apumpdrawswaterthroughawatersoftenerunit/ionexchangerandintothebaseofthemachine.Hereaheaterheatsthewatertoasuitabletemperatureandthedishwasherproductdispenseropenssothatthedishwashertabletorpowdercontainingamixofchemicalsfallsintothewaterafterapproximately5‐10minutes,whenthewaterisstillcold.

Apumpthenforcesthewaterthroughtworotatingsprayarmswhichspraythewaterontothedishesarrangedintwobaskets,Figure3.

Figure3:Thewashingcycle(courtesyofhowstuffworks.com)

Thedirtywaterisremovedfromthebaseofthemachine,Figure4.

Figure4:Thedrainingcycle(courtesyofhowstuffworks.com)


Thisisthenrefilledwithcleanwaterwhichissprayedonthedishestorinsethem.

Youcanfindmoredetailfromthelinksbelow.

http://home.howstuffworks.com/dishwasher.htm

http://www.dishwasher‐care.org.uk/best.html

Howdoesadishwasherwork?(2of2)Atvariouspointsinthecycle,thewaterisheatedtoasuitabletemperaturefortheprocesstakingplace.TheprofileofatypicalwashingcycleisshowninFigure5inwhichtemperatureisplottedverticallyandtimehorizontally.

Hotwaterisshowninred,cold(ieroomtemperature)inblueandsectionsinvolvingtheionexchangeresininwhite.

Figure5:Atypicaldishwashercleaningcycle.Onlyintensiveprogramsuseprewashcycles.NormalorEcoprogramsimmediatelystartwiththemaincycle.Thedetergentisonlydosedinthemain

wash.

SofteningthewaterThefirstchemicalprocessindishwashingissofteningthewater.WaterinmostareasoftheUKcontainssignificantlevelsofCa2+andMg2+(andinsomecasesFe3+)ions.

Thesearisefromthefactthatinmanyareaswatersoaksthroughlimestonerocksanddissolvessomecompoundscontainingtheseions.Thisisassistedbythefactthatrainwaterisnaturallyacidicduetodissolvedcarbondioxide.Sotapwatercontainsdissolvedcompoundssuchascalciumhydrogencarbonateandmagnesiumsulfate.


Figure6:HardnessofwaterintheUK.Theunitsaremg/l,iemgdm‐3,ofcalciumcarbonateequivalent(CourtesyofCaterchemUK)

Themap,Figure6,indicatesgenerallythehardnessofwaterinvariouspartsoftheUK.Thesemetalionsinhardwatercaninterferewithanumberofthechemicalprocessesinvolvedindishwashing,whichareexplainedbelow,anditisthereforebettertoremovethem.Theymayalsocauselimescaletobuildupinsidethemachine.TherearemoredetailsofthechemistryofhardwateranditseffectoncleaningprocessesinCalgon.

Dishwasherssoftenwaterbypassingitthroughanionexchangeresinbeforeitentersthemachineitself.Theresiniswell‐named–itliterallyexchangesdoublyandtriplypositively‐chargedmetalionsforsinglypositively‐chargedsodiumionswhichdonotaffectthewashingprocesses.

Question1Explainwhymetalsalwaysformpositiveions.Thiscannotgoonforever,ofcourse‐theresineventuallyrunsoutofsodiumionstoexchange.Topreventthissituationtheresinisregeneratedbyflushingaconcentratedsolutionofsodiumchloridethroughit.Thisreplacesthecalciumandmagnesiumionsontheresinforsodiumionsagainandthecalciumandmagnesiumionsareflushedaway.Fromtimetotime,puresalt(sodiumchloride)mustbeaddedtothereservoirinthedishwasherwherethesaltsolutionismade.Tablesaltshouldnotbeused,asmostbrandsofthiscontainmagnesiumsulfateasananti‐cakingagent‐thelastthingrequiredinawatersoftener.


Thisprocessisessentiallyareversiblereactionandcanberepresentedbyanequation,whereRrepresentstheresin:

RNa+Na+(s)+Ca2+(aq) RCa2+(s)+2Na+(aq)

Althoughitisareversiblereaction,itneverreachesequilibriumasinbothsofteningandregenerationthewaterisconstantlypassingoverthesolidresin.

Whatdoesadishwashercleaningagentcontain?Thepurposeofadishwashercleaningagentistoremovedirt(oftencalled‘soil’)fromthearticlesinsidebydissolvingitormakingitintoasuspensioninthewashingwater.Itmustalsopreventitsre‐depositiononthearticlessothatthesoilcanbecarriedawaybythewashingwater.

Itmustbechemicallycompatiblewithallthematerialsbeingwashedandalsowiththematerialsfromwhichthedishwasheritselfismade.

Dishwashertabletsandpowderscontainasurprisingmixofchemicals,farmorethanjustthedetergentyoumightexpect.

Theseareasfollows:

Surfactants(detergents)‐thesepromotemixingbetweenoil‐andfat‐basedsoilandwater.

Alkalis‐theseemulsifygreaseandadjustthepHofthewatertotheoptimumfortheothercomponentstowork

Bleaches‐theseoxidisecolouredsubstancestocolourlessones Biosubstances‐theseareenzymesthatbreakdownstarch‐andprotein‐based

soils Builders‐thesehelptosoftenwaterandtrapmetalionsthatwouldinterfere

withthecleaningprocessandholddirtinsolution Auxiliaries‐theseincludesubstancesusedtomakeanddisintegratethetablet

aswellascoloursandperfumes

Oneproblemthatmaybeencounteredisgettingallthesedifferentingredientstoworktogetherwhentheyhavedifferentoptimumconditions.Enzymes,forexample,workbestatmoderatetemperaturesaround50°C‐seeFigure7.Theyaredenaturedandwillnolongerworkiftheyhavebeenexposedtotemperaturesmuchabovethisforanylengthoftime.


Figure7:Thetemperaturedependenceofenzymeactivity.Proteasesdecomposeproteinsandamylasesdecomposestarch‐basedsoils

Ontheotherhand,greaseremovalwillworkbestathightemperatureswhenfatsmelttooilsmakingthemeasiertoremove.And,ofcourse,allchemicalreactionsgofasterathighertemperatures‐twiceasfastforevery10°Criseisausefulruleofthumb.

ThereisasimilarissuewithpH.CleaningtakesplacebestatalkalinepHsbuttheoptimumpHformostenzymesisneutraltomildlyalkaline‐theyaredenaturedinstronglyacidicoralkalineenvironments.TheoptimumpHforthebleach,however,isaround10.

Onefurthercomplicationforthedesignersofdishwashersandtheirassociatedcleaningproductsistodowithuserbehaviour;itisusualtowashtogetheralargevarietyofmaterialse.g.glass,porcelain,plastics,anddifferentmetals.Thisisincontrastwithclotheswashing,whereusersseempreparedtoseparateoutdifferenttypesofmaterial‐wool,synthetics,cottonetc.Theoptimumconditionsformanyofthematerialsinthedishwasherwilldiffer.

Surfactantsordetergents(1of2)Greasystainsdonotmixwithwaterbecausethemaininteractionsbetweenwatermoleculesarehydrogenbondingandthosebetweenmoleculesofoilsandfats(whichconstitutegrease)arevanderWaalsforces.

Togetwaterandgreasetomixweusemoleculescalledsurfactantsordetergents.Thesetwotermsrefertoessentiallythesamething‐moleculesthatare‘tadpoleshaped’inthattheyhaveanon‐polar‘tail’andapolarorionic‘head’.The‘tail’canformvanderWaalsbondswithnon‐polargreasemoleculeswhilstthe‘head’canformhydrogenbondswithwater,Figure8.Thisisanexampleofthe‘likedissolveslike’rule.


Figure8:Thenon‐polartails(inyellow)of‘tadpoleshaped’detergentmoleculesmixwithgrease,whilethepolarheads(inred)mixwithwater,thusforcingthegreaseandwatertomix

Thereareessentiallythreetypesofsurfactants–anionic,cationicandnon‐ionic.

Anionicsurfactantshaveanegativelychargedhead.Commontypesincludesoaps,Figure9,andalkylbenzenesulfonates,Figure10.

Figure9:Sodiumstearate(asoap)–ananionicsurfactant

Figure10:Sodiumdodecylbenzenesulfonate–ananionicsurfactant

Cationicsurfactantshaveapositivelychargedhead.Commontypesincludealkylammoniumchlorides,Figure11.


Figure11:Trimethylhexadecylammoniumchloride–acationicsurfactant

Nonionicsurfactantshaveapolar,butuncharged,head.Commontypesincludepolyethyleneethoxylates,Figure12.

Figure12:Apolyethyleneethoxylate–anonionicdetergent

Surfactantsordetergents(2of2)Surfactantsareprobablytheingredientsoneexpectsinadishwasherproduct‐weoftencalltheproductsimplyadishwasherdetergent.However,theyplayarelativelyminorroleintheproduct.Non‐ionicpolyethyleneethoxylatesarechosenasthemainsurfactantsinFinishastheyproducerelativelylittlefoam.

Theirmainfunctionistoenablegreasysoilstomixwithwater.Muchofthesoilondishesisheldtherebygrease.Greasesandoilsarechemicallysimilar;theyconsistlargelyofestersoffattyacids‐longchaincarboxylicacids‐withglycerol,seeFigure13.Thesecontainlonghydrocarbonchainswhichareessentiallynon‐polar,andthereforedonotformhydrogenbondsordipole‐dipolebondswithwatermolecules.

Figure13:Atypicalfatoroil‐whichitisdependsonthechainlengthsofthethreefattyacidsandwhetherornottheirhydrocarbonchainsarebranched


Whendissolvedinwater,surfactantstendtoclusteratthesurface(hencethename),sothattheirnon‐polartailscanstickoutofthewater.Surfactantmoleculescanformstructurescalledmicelles:thesearesmallspheresmadeofsurfactantthattrapoilmoleculesandenablethemtodissolveinthewater.

Thedifferencebetweenfatsandoilsisoneofmeltingpoint‐atroomtemperaturefatsaresolidandoilsareliquidduetotheirshorterhydrocarbonchains.Solidgreasesadheretosurfacesbetterthanliquidoilswhichjusttendtorolloff.Soahightemperaturewhichturnsfatsintooilsishelpfulforcleaning.

AlkalisManycleaningproductsactbestinsomewhatalkalinesolution.

Thisisbecausealkalis

emulsifygreasebyreactingwithinsolublefattyacidstoformionicsaltswhicharesoluble

protectthemetalofwashingmachinesanddishwashersfromacidcorrosion helptoreducere‐depositionofdirtthathasbeenremoved,bycoatingparticlesof

itwithnegativelychargedhydroxideions–thismeansthedirtparticlesrepeleachotherandremaininsuspensionratherthanclumpingtogethertoformlargeaggregateswhichwouldtendtoprecipitateoutontodishes

percarbonate‐basedbleachesworkbestinsomewhatalkalinesolutionThedishwasherwateriskeptataboutpH10–significantlyalkaline.Atthehightemperatureofthewash,hydroxideionsreactwiththemoleculesofgreaseandbreakthemupintosaltsoffattyacidsandglycerol.Thisisthemainmechanismforremovinggrease.

ThereactionisshowninFigure14andisthesameasthatformakingsoapfromfatsandoils–saponification.

Figure14:Thesaponificationofgrease


Question2a)Explainwhytheproductsoftheabovereactionaremoresolublethantheoriginalfatmolecules.b)Givethesystematicnameofglycerol.

Sodiumcarbonate,Na2CO3,isusedinthedishwasherproducttomakethesolutionalkaline.Itisthesaltofastrongalkali(sodiumhydroxide)andaweakacid(carbonicacid)andisthereforealkaline.Itdissociatesinsolutiontoformcarbonateions,CO32‐,whichhelptomaintainthepHofthewashingwaterataround10.

Question3Explainhowthecarbonateioncanmakeanaqueoussolutionalkaline.Bleaches(1of2)Bleachesareusedtooxidisecolouredsubstancestocolourlessones.

Thebleachusedissodiumpercarbonate.ThisisawhitegranularpowderofformulaNa2CO3.3H2O2.

Figure15:Structureofsodiumpercarbonate

Inwateritbreaksdownintosodiumcarbonateandhydrogenperoxide.

2Na2CO3.3H2O2(aq) 2Na2CO3(aq)+3H2O2(aq)

Hydrogenperoxideistheactiveoxidisingagentasitinturnbreaksdowntooxygenandwater.Thebeautyofthissystemisthatthestartingmaterialisarelativelystablepowder(althoughitobviouslymustbekeptdry)andtheby‐products(sodiumcarbonateandwater)areinnocuous.

Question4a)Writeanequationforhydrogenperoxidedecomposingtooxygenandwaterb)Usethisandtheequationabovetoworkouthowmanymolesofoxygencanbeobtainedfrom2molesofsodiumpercarbonate.


c)Nowworkoutthesequantitiesintermsofgramsofsodiumpercarbonateandoxygen.d)Onecommercialspecificationforsodiumpercarbonateguarantees‘notlessthan13%activeoxygen.Fromyourcalculationabove,isthisrealistic?

Bleaches(2of2)Activatorsareaddedtohelpthebleacheswork.Theseareessentially,andactsimilarlyto,catalysts.Theyspeedupthereactionsothatitcantakeplaceeffectivelyatlowertemperaturesthanwithouttheactivator.However,activatorsareconsumedstoichiometricallywhilstcatalystsarenot.

Theuseofactivatorsmakesthebleachesmorecompatiblewiththeenzymesinthedishwasherformulation.

Question5Explainthephrase‘Thismakesthebleachesmorecompatiblewiththeenzymes.’

Figure16showbleachactivityandenzymeactivityatdifferentstagesofthewashcycle.

Figure16:Enzymeactivity(blue)andbleachactivity(red)atdifferentstagesofthewashcycle

BiosubstancesEssentially,theseareenzymes–

proteases(tohelpbreakdownproteins)

amylases(tohelpbreakdownstarches)

Question6Suggestfoodsthatarebasedona)proteinsb)starches


Proteasesdecomposebig,water‐insolubleproteinmoleculesintosmallsolubleunits.

C C

H

H

N C C

H

CH3

H O

N

H O

N

H

C

H

CH2SH

C

O

Figure17:Partofaproteinmolecule

Amylasesdecomposebig,water‐insolublestarchmoleculesintosmallsolubleunits.

O

OH

OH

CH2OH

O

O

OH

OH

CH2OH

O

O

OH

OH

CH2OH

O

O

OH

OH

CH2OH

O

Figure18:Partofastarchmolecule

Question7Suggestwhatarethe‘smallsolubleunits’producedbythebreakdownofa)proteinsb)starches

Inbothcases,thebreakdownprocessisahydrolysisreaction(reactionwithwater).

Question8a)LookatthestructuresinFigures17and18.Eachhasoneofthelinkageswherehydrolysistakesplacecircled.Drawtheproductsafterhydrolysishastakenplaceforpartofaproteinmoleculeb)LookatthestructuresinFigures17and18.Eachhasoneofthelinkageswherehydrolysistakesplacecircled.DrawtheproductsafterhydrolysishastakenplaceforpartofastarchmoleculeAsindicatedpreviously,enzymeshaveoptimumpHsandtemperatures,sothishastobebuiltintothedesignofthewashingcycle.Enzymeswillbedenaturedandceasetofunctionafterthemainwashcycleofthedishwasherprogram.

BuildersBuildershaveanumberoffunctionsincludingsoftening,bufferingandemulsifying.


Ca2+ionshavelargelybeenremovedfromthestartingwashingwaterbytheionexchangeresininthedishwasherbutmoremayoriginatefromthesoilitself.Thesecanbedealtwithbythebuilder.

Buildersusedincludephosphates,citratesandpolycarboxylates,Figure19.Noticethateachonehasoxygenatomswithanegativecharge.ThesecanformcomplexeswithCa2+ionsandeffectivelyremovethemfromsolution.

HO P O

O-

O

P O P OH

O- O-

OO

phosphate

H C C C

OH

COO-COO-COO-

H

HH

citrate

COO- COO- COO- COO-

polycarboxylate

Figure19:Structuresofsomecommonbuilders

Question9a)WhatfeaturedotheoxygenatomshavewhichenablesthemtoformabondwithCa2+ions?b)Whatnameisgiventothistypeofbonding?

TheCOO‐groupscanacceptprotonsfromacidicwaterandkeepitalkaline.

Itisoftenthoughtthatphosphatesarenolongerusedinhouseholdproductsbecausetheycangetintowatercoursesandcauseeutrophication‐theovergrowthofplantscausedbythefertilisingeffectofphosphates.InfactthereisnosuchblanketbanandphosphatesarestillusedindishwashingproductsasthecontributiontothetotalP‐loadislessthan5%.Themainquantityiscomingfromagriculturalland,humanmetabolismandindustrialwastewater.

RinseaidThefinalpartofthewashingcycleisarinsewithcleanwaterthathasbeensoftenedbytheionexchangeresin.Inmostmachinesitispossibletoaddarinseaidtothiscyclefromaseparatecompartmenttothemaindishwashingproduct.


Rinseaidisasurfactantthatreducesthesurfacetensionofwater.Surfacetensionisthe‘skin’effectonthesurfaceofwaterthatmakesit‘curlup’intodropletsoncleansurfaces,seeFigure20,ratherthanspreadinathinlayeroverthewholesurface.

Figure20:Thesurfacetensionofwatercausestheformationofdroplets

Surfacetensioniscausedbyhydrogenbondsbetweenwatermoleculesatthesurfaceofliquidwater.Surfactantmoleculesclusteratthesurfaceofawaterdropletbecausetheir‘tails’donotformhydrogenbondswithwaterandthesurfaceistheonlyplacewherethiscanoccur.Thisdisruptsthehydrogenbonding,loweringthesurfacetensionandallowingthewatertospreadout,leavingagreatersurfaceareawhichspeedsevaporationandhencedrying.

Italsoallowsthewatertodrainmoreeasilyfromthesurfacesofthedishesasshownbelow.

Figure21:Rinseaidproducesdropletswithagreatersurfaceareatospeeddryinganddraining


RecentdevelopmentsDishwashertechnologycontinuestoimprove;newermachinesmayhavesensorswhichcanbeusedtodeterminethebestprogramforawash.Theseinclude:

determinationoftheamountofsoilinthewashingwater

measurementofwaterhardness

determinationofdishloadQuestion10Suggesthowthehardnessofthewaterenteringadishwashermightbemeasured.Remembertheresultmustbeobtainedquicklyand‘electronically’sothatitcanbefedbacktocontrolthemachine,soatitration,forexample,wouldnotdo.Hint,hardnessiscausedbyaqueousCa2+andMg2+ions.Forexampletheamountofsoilinthewatercanbemeasuredbyshiningalightthroughasampleofwaterandnotinghowmuchisabsorbed–themorelightabsorbed,thedirtierthewater.

Figure22:Dishwashinginaction(courtesyofhowstuffworks.com)

DifferentformulationsFinishbrandedproductsaresoldinanumberofformswithdifferentformulations,Figure23.


Figure23:DifferentformsandformulationsofFinish

Theingredientsofjustoneformulation,FinishPowerballclassictabletsregular,arelistedinFigure24.

Figure24:IngredientsfoundinFinishPowerballclassictabletsregular


Someofthesehavebeendiscussedabovebutthereareanumberofothersthatarebeyondthescopeofthispiece.Allofthemcontributetothefinalproductinsomeway.

FurtherinformationSeveralvarietiesofFinish™aresoldintheUKbyReckittBenckiser(http://www.finish.co.uk/).Thereareotherbrandedproductswhichworkinasimilarway.

Teachersandstudentswhoareinterestedinmoredetailsabouthouseholdproductsmightwishtoconsultthefollowingbook:

G.Wagner etal, HouseholdCleaning,CareandMaintenance‐Products‐Chemistry,Application,EcologyandConsumerSafety, VerlagfürchemischeIndustrie ISBN3‐87846‐241‐7

AcknowledgementsTheRoyalSocietyofChemistrywishestothankChrisJones,AlexandraHaryandGunnarNoedingofReckittBenckiserforhelpinpreparingthismaterial.

TheRoyalSocietyofChemistrygratefullyacknowledgesthatthisprojectwasinitiallysupportedbyReckittBenckiserin2007.ReckittBenckiserconductedafinalreviewin2013sopleasenotethatcertaininformationmaybeoutofdate.

QUESTIONSANDANSWERSQuestion1Explainwhymetalsalwaysformpositiveions.Metalsallhaveone,twoorthreeelectronsintheiroutershells.Itiseasiertolosethesetoattainafulloutershellofelectrons(anoblegasarrangement)thantogainelectrons.Lossofnegatively‐chargedelectronsproducespositiveions.

Question2a)Explainwhytheproductsoftheabovereactionaremoresolublethantheoriginalfatmolecules.Oneproductisanegativeionwhichcaninteractwithwatermoleculesbetterthananeutralmolecule.Theotherisasmallmoleculewithahighproportionof–OHgroupsthatcanhydrogenbondwithwater.

b)Givethesystematicnameofglycerol.Propane‐1,2,3‐triol.

Question3Explainhowthecarbonateioncanmakeanaqueoussolutionalkaline.Itcanacceptprotons(H+ions)fromthesolutiontoformHCO3‐,leavinganexcessofOH‐ions.

Question4a)Writeanequationforhydrogenperoxidedecomposingtooxygenandwater


2H2O22H2O+O2

b)Usethisandtheequationabovetoworkouthowmanymolesofoxygencanbeobtainedfrom2molesofsodiumpercarbonate.2molsodiumpercarbonateproduces3molhydrogenperoxide,whichwouldproduce1.5moloxygenmolecules.

c)Nowworkoutthesequantitiesintermsofgramsofsodiumpercarbonateandoxygen.2molsodiumpercarbonatehasamassof314g

1.5moloxygenmoleculeshasamassof48g

d)Onecommercialspecificationforsodiumpercarbonateguarantees‘notlessthan13%activeoxygen.Fromyourcalculationabove,isthisrealistic?(48/314)x100=15.3%,sothespecificationisrealistic.

Question5Explainthephrase‘Thismakesthebleachesmorecompatiblewiththeenzymes.’Enzymeshavetheiroptimumtemperatureataround50oC.Abovethistemperaturetheproteinsfromwhichtheyaremadedenature.Thebleachingreaction,ontheotherhand,willcontinuetoworkfasterasthetemperatureincreasesandso,ideally,ahighertemperaturethan50oCwouldbebetter.

Question6Suggestfoodsthatarebasedona)proteinsMeats,cheese,eggetc

b)starchesBread,pasta,riceetc

Question7Suggestwhatarethe‘smallsolubleunits’producedbythebreakdownofa)proteinsAminoacids

b)starchesSugars

Question8a)LookatthestructuresinFigures17and18.Eachhasoneofthelinkageswherehydrolysistakesplacecircled.Drawtheproductsafterhydrolysishastakenplaceforpartofaproteinmolecule

C C

H

H

N C C

H

CH3

H O

N

H O

N

H

C

H

CH2SH

C

O

HOH


b)LookatthestructuresinFigures17and18.Eachhasoneofthelinkageswherehydrolysistakesplacecircled.Drawtheproductsafterhydrolysishastakenplaceforpartofastarchmolecule

O

OH

OH

CH2OH

O

O

OH

OH

CH2OH

O

O

OH

OH

O

CH2OH

O

O

OH

OH

CH2OH

OH H

Question9a)WhatfeaturedotheoxygenatomshavewhichenablesthemtoformabondwithCa2+ions?Lonepairsofelectrons.

b)Whatnameisgiventothistypeofbonding?Dativeorco‐ordinatebonding.

Question10Suggesthowthehardnessofthewaterenteringadishwashermightbemeasured.Remembertheresultmustbeobtainedquicklyand‘electronically’sothatitcanbefedbacktocontrolthemachine,soatitration,forexample,wouldnotdo.Hint,hardnessiscausedbyaqueousCa2+andMg2+ions.Waterhardnesscouldbedeterminedbymeasuringtheelectricalconductivityofthewater–theharderthewater,themoreionsandthehighertheconductivity.(Othersuggestionsarepossible)