Chemistry in your cupboard: Finish
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Finish is a registered trade mark of the Reckitt Benckiser group of companies. Last reviewed by Reckitt Benckiser in 2013 Chemistry in your cupboard: Finish Introduction Machine dishwashing is a complex process which has to rely on chemistry rather than manual effort to clean dishes. Dishwasher cleaning products contain a huge range of chemicals including surfactants or detergents, alkalis, bleaches, biosubstances and builders. Each of these has a distinct role in the cleaning of dishes but the difficulty is getting all these working together when they have different optimum conditions. Finish™ is a brand with a range of products available in different formulations but all based on the same broad principles. Links to the curriculum This section contains information relevant to the following areas of your chemistry curriculum: Rates of reactions Group 7 elements Group 1 and 2 elements Biochemistry (proteins, fats and carbohydrates) Acids and bases FINISH According to the Office of National Statistics, in 2008 almost 40% of homes in the UK had a dishwasher, up from around 25% in 1998. It is tempting to think of machine dishwashing as comparable to hand washing of dishes but in fact it is a much more complex process and involves a great deal more chemistry. Hand dishwashing relies mostly on mechanical effort ‐ continuing to brush or sponge (with the help of hot water and a detergent), until the dishes appear clean. With machine dishwashing, mechanical effort counts for less, and the chemistry has to do the cleaning. However, the conditions for machine washing can be both hotter and more alkaline that could be withstood by human hands. Here we will look at some of the chemistry that goes on inside the dishwasher and relate it to chemistry that you already know. The science of dishwasher products is complex and we can only cover the basics here. Did you know? Josephine Cochrane invented the modern dishwasher in 1886.
Transcript of Chemistry in your cupboard: Finish
FinishisaregisteredtrademarkoftheReckittBenckisergroupofcompanies.LastreviewedbyReckittBenckiserin2013
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.
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Cochranewasawealthysocialitewhoseservantskeptchippingherfinechinawhilehandwashingit.Shedevelopedarackandwaterjetsystemthatwasfirstdemonstratedatthe1893ChicagoWorldFair.
Figure1:AproductfromtheFinishrange
Howdoesadishwasherwork?(1of2)Beforeweconsiderthechemistry,weneedtounderstandthemechanicsofadishwasher,Figure2.Thisisessentiallyverysimple.
Figure2:Thebasiclayoutofadishwasher(courtesyofhowstuffworks.com)
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Apumpdrawswaterthroughawatersoftenerunit/ionexchangerandintothebaseofthemachine.Hereaheaterheatsthewatertoasuitabletemperatureandthedishwasherproductdispenseropenssothatthedishwashertabletorpowdercontainingamixofchemicalsfallsintothewaterafterapproximately5‐10minutes,whenthewaterisstillcold.
Apumpthenforcesthewaterthroughtworotatingsprayarmswhichspraythewaterontothedishesarrangedintwobaskets,Figure3.
Figure3:Thewashingcycle(courtesyofhowstuffworks.com)
Thedirtywaterisremovedfromthebaseofthemachine,Figure4.
Figure4:Thedrainingcycle(courtesyofhowstuffworks.com)
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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.
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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.
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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.
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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.
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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.
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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
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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
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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.
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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
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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.
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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.
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Rinseaidisasurfactantthatreducesthesurfacetensionofwater.Surfacetensionisthe‘skin’effectonthesurfaceofwaterthatmakesit‘curlup’intodropletsoncleansurfaces,seeFigure20,ratherthanspreadinathinlayeroverthewholesurface.
Figure20:Thesurfacetensionofwatercausestheformationofdroplets
Surfacetensioniscausedbyhydrogenbondsbetweenwatermoleculesatthesurfaceofliquidwater.Surfactantmoleculesclusteratthesurfaceofawaterdropletbecausetheir‘tails’donotformhydrogenbondswithwaterandthesurfaceistheonlyplacewherethiscanoccur.Thisdisruptsthehydrogenbonding,loweringthesurfacetensionandallowingthewatertospreadout,leavingagreatersurfaceareawhichspeedsevaporationandhencedrying.
Italsoallowsthewatertodrainmoreeasilyfromthesurfacesofthedishesasshownbelow.
Figure21:Rinseaidproducesdropletswithagreatersurfaceareatospeeddryinganddraining
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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.
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Figure23:DifferentformsandformulationsofFinish
Theingredientsofjustoneformulation,FinishPowerballclassictabletsregular,arelistedinFigure24.
Figure24:IngredientsfoundinFinishPowerballclassictabletsregular
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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
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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
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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)
