STEM%Outreach%at%CU%Denver%
Activity'Description'
'
Salad%Dressing%Science'
Contributed'by:'Rebecca'Zabinski'and'Cierra'Walker'
Adapted'from:'sciencefriday.com'
'
Purpose:'to'introduce'emulsifiers'in'the'context'of'homemade'salad'dressing'
'
Background%
'
Water'molecules'are'composed'of'two'hydrogen'atoms'and'an'oxygen'atom.'
The'structure'in'which'these'atoms'are'bonded'creates'positive'and'negative'
charges'at'opposite'ends'of'the'molecule.'As'a'result,'other'molecules'with'
similar'electric'charges'mix'well'with'water'and'are'called'hydrophilic.'
Molecules'that'have'an'even'distribution'of'electric'charge'do'not'mix'well'
with'water'and'are'called'hydrophobic.'
'
Emulsifiers'are'molecules'used'to'prolong'the'mixture'of'hydrophilic'
molecules'with'hydrophobic'molecules.'For'example,'emulsifiers'are'used'to'
maintain'the'desired'consistencies'in'margarine,'ice'cream,'bread,'chocolate,'
and'salad'dressing.'
'
Overview%
%
This'activity'explores'the'behavior'of'emulsifiers'and'their'effectiveness'in'
the'context'of'home'made'salad'dressing.'Specifically,'students'will'compare'
the'separation'times'of'oil'and'vinegar'mixtures'using'different'emulsifiers.'
'
Materials%'
'
–'5'50mL'test'tubes'(per'group)'
'
–'75mL'(5'Tbs)'of'olive'oil'(per'group)'
–'75mL'(5'Tbs)'of'white'vinegar'(per'group)'
M'5mL'(1'tsp)'of'each'of'the'following'(per'group):''
tomato'paste'
mustard'
garlic'powder'
salt'
–'Clock'or'stopwatch'
'
Protocol'
'
1. Write'down'the'question'this'experiment'was'designed'to'answer'and'state'your'
hypothesis.'
2. Clean'five'50mL'test'tubes.'
3. Label'the'five'test'tubes'control,'tomato'paste,'mustard,'garlic'powder,'and'salt.'
Into'the'nonMcontrol'test'tubes,'add'5ml'(1'tsp)'of'the'ingredient'corresponding'to'
the'test'tube’s'label.'
STEM%Outreach%at%CU%Denver%
Activity'Description'
'
4. Into'every'test'tube,'add'15mL'(1'Tbs)'of'olive'oil'and'15mL'(1'Tbs)'of'white'
vinegar.'Observe'the'layering'of'the'oil'and'vinegar'in'the'control'test'tube.'
5. Vigorously'shake'each'test'tube'for'about'5'seconds'to'mix'the'ingredients.'As'
soon'as'you'stop'shaking,'start'the'stopwatch'and'watch'for'signs'of'separation.'
6. When'most'of'the'oil'has'separated'from'the'vinegar,'record'the'amount'of'time'it'
takes'each'test'tube'to'separate.'If'the'oil'and'vinegar'have'not'separated'after'15'
minutes,'record'“over'15'minutes.”'
7. Repeat'time'trials'as'desired.'
'
Discussion%Questions'
'
M'How'do'we'measure'separation?'How'do'we'know'if'an'ingredient'is'an'
emulsifier?'
M'Did'the'control'test'work?'Why'does'separation'occur?'
M'Based'on'the'data,'which'ingredients'are'likely'emulsifiers?'Why'are'or'
aren’t'they?'Is'this'what'was'expected?'
M'Is'there'discrepancy'among'separation'times'for'different'groups?'What'
might'cause'differences'in'separation'times?'
M'Which'ingredient'would'you'recommend'for'making'salad'dressing?'
'
Modifications%and%Extensions'
'
The'experiment'can'be'run'with'a'variety'of'potential'emulsifiers.'Students'
could'also'be'challenged'to'determine'which'ingredients'in'common'salad'
dressing'recipes'are'hydrophilic,'hydrophobic,'or'emulsifiers.'Additionally,'
students'can'be'challenged'to'experimentally'find'the'best'emulsifier'from'
among'a'list'of'ingredients'in'salad'dressing'recipes.''
'
The'conversation'surrounding'hydrophilic'and'hydrophobic'molecules'can'
be'supplemented'with'the'fatty'acids'in'animal'cell'membranes,'which'create'
hydrophilic'and'hydrophobic'regions'that'aid'in'transporting'nutrients'in'to'
and'out'of'cells.'
'
Some%References%
%
http://www.sciencefriday.com/blogs/08/15/2014/saladMdressingMscienceM
emulsions.html'
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http://www.foodnetwork.com/recipes/articles/50MsaladMdressingM''
recipes.html?oc=linkback''
'
'
Attachments'
'
Slides'with'introduction'and'protocol'overview'
'
Compiled'by'Axel'Brandt'as'part'of'the'CU'Denver'Community'STEM'Clubs'program.'Special'thanks'to'
h"p://www.npr.org/blogs/thesalt/2014/06/25/325189711/kandinsky@on@a@plate@art@inspired@salad@just@tastes@be"erC
•  HydrophobicC
•  HydrophilicC
DefiniFonsC
•  HydrophobicC=ChydroC+CphobiaC
•  HydrophilicC=ChydroC+CphiliaC
DefiniFonsC
h"p://www.sciencefriday.com/blogs/08/15/2014/salad@dressing@[email protected]
H2OCWaterCisChydrophilicC
h"p://www.oliveoilsource.com/page/chemical@characterisFcsC
CH3(CH2)nC00HCOilCisCaCfa"yCacidC
mostlyChydrophobicC
h"p://dkcorporaFon.tradeindia.com/emulsifier@for@paints@solvents@vegetable@[email protected]
EmulsifiersC
RossCetCal.,C2005C
How$do$we$answer$scien-fic$ques-ons?$
The$Scien-fic$Method$
–  NegaFveC
–  PosiFveC
•  Controls:C
•  HypothesisC
•  QuesFonC
SaladCDressingCScienceCExperimentC
–  RecordCdataCandCanalyzeCresultsC
–  ShakeCtoCmix,CthenCmeasureCseparaFonCFmeC
1@15minC
–  AddCvinegar,Coil,CandCemulsifierCtoCtestCtubesC
–  AddCvinegarCandCoilCtoCcontrolCtubeC
•  ProtocolC
SaladCDressingCScienceCExperimentC
–  OilC
–  VinegarC
–  4CTestCtubesC
–  TomatoCpasteC
–  MustardC
–  GarlicCpowderC
–  1CtspCC
–  ClockCorCstopwatchC
–  EmulsifierCdataCsheetC
•  MaterialsC
SaladCDressingCScienceCExperimentC
–  SeparaFonCFmeCisClongerCthanCcontrol.C
•  HowCdoCweCknowCwhatCaCposiFveCresultCforCanC
emulsifierClooksClike?C
–  TimeCtheCcontrol:CvinegarCandCoilC
•  HowCdoCweCmeasureCseparaFon?C
MakingCsureCourCexperimentCworks:C
UsingCcontrolsCinCscienceC
•  BasedConCyourCobservaFonsCofCseparaFonCFme,CwhichC
emulsifierCwouldCyouCrecommendCusingCforCmakingC
saladCdressing?CC
•  DidCtheCmixturesCwithCtheCemulsifiersCtakeCmoreCorClessC
FmeCtoCseparateCthanCyourCcontrol?CIsCthisCwhatCyouC
expected?CCWasCitCreplicatedCbyCotherCgroupsCinCtheC
class?C
•  RecordCyourCgroupCresultsConCtheCboard.C
•  DidCtheCcontrolCtestCwork?CCWhyCdoesCseparaFonCoccur?C
AnalyzingCResultsC
CellCmembranesCareCmadeCofCfa"yCacidsC