lab activity: measuring calories in food - christina … · 2017-01-24 · lab activity: measuring...
TRANSCRIPT
LabActivity:MeasuringCaloriesinFoodLabActivity:MeasuringCaloriesinFoodScientistsuseadevicecalleda“calorimeter”,showninFigure1,tomeasuretheamountofchemicalpotentialenergyinallsortsofmaterials..Todeterminethechemicalenergyofamaterial,scientistsfirstmeasurethemassofasampleofthematerial.Theythenplacethesampleinasealedcontainercalleda“bomb”.Theyputthebombinawell-insulatedcontainerfilledwithaknownvolumeofwater.Anelectricalsparkfrominsidethebombstartsthesampleburning.Thewaterinthecontainerabsorbstheenergyreleasedbytheburnedsample.Athermometermeasuresthechangeinthetemperatureofthewater.Thepotentialenergyoftheoriginalmaterialisequaltothethermalenergytransferredtothewater.Figure1.Calorimeter“Bomb”
Inthisactivity,youwilluseasimplifiedcalorimeterdevicemadeoutofasodacantomeasuretheamountofcaloriesinasampleoffood.SAFETYMEASURES
1. Wearsafetygogglesduringthisinvestigation2. Longhairmustbetiedback.3. Ifanythingotherthanthefoodmaterialbeginstoburn,notifyyourteacher
immediately4. Beespeciallycarefultokeepclothingandsleevesawayfromtheopenflame.5. Thecanmaybecomequitehot.Carefullyfollowallinstructionswrittenin
theprocedureandprovidedbyyourteacher.6. Anoteaboutfoodsensitivities:ifyouareallergictoanyofthefooditems,
pleasenotifyyourteacher.Sensitiveindividualsshouldnotparticipateintheburningofthematerialthatmayresultinexposure.
7. Noeatingordrinkinginthelab.
LabActivity:MeasuringCaloriesinFoodLabActivity:MeasuringCaloriesinFood
Materials:Foreachgroup:Sodacan(empty)GlassStirringrodRingstandandringThermometerprobe(lab-quest)MiniadapterElectronicbalanceCorkMetalpaperclipGraduatedcylinderProcedure:CLEARSPACEOFALLFLAMMABLES1. Usingthegraduatedcylinder,obtain50mLofwaterandcarefullypourit
intothesodacan.2. Determinethemassofthewaterandrecordyourfindinginthedatatable
provided.(Hint:densityofwateris1g/mL)3. Holdthepapercliphorizontallyandbendtheouterendupwardsuntilit
isata90degreeangletotherestofthepaperclip.4. Obtainacorkandcoverthecorkwithaluminumfoil.5. Insertthepaperclipintothefoil-coveredcork.6. Insertthestirringrodthroughthesodacantabandpositionthecanin
theringstandsothatthestirringrodsupportsit(seeFigure2).
Figure2.
LabActivity:MeasuringCaloriesinFoodLabActivity:MeasuringCaloriesinFood
7. Adjusttheringstandsothatthecanisapproximately4cmabovethefood
sample.
8. Suspendthethermometerinsidethecanandlettheedgeofthethermometercoverrestagainstthecan(seefigure3).
Figure3.
9. Attachthetemperatureprobetothelab-questminiadapterandconnectthistothedesktopcomputer
10. Open“loggerpro”andtakeaninitialtemperaturereadingofthewater.11. Measurethemassofyourfoodmaterialandrecorditinthedatatable.12. NowattachthefoodtothepaperclipasshowninFigure4.
LabActivity:MeasuringCaloriesinFoodLabActivity:MeasuringCaloriesinFood
Figure4
13. Showyourteacheryourexperimentalset-upbeforeusingalightertoigniteyourfoodmaterial.
14. Onceyouhavereceivedapprovalforyourexperimentalsetup,initiatedatacollectioninlogger-proandigniteyourfoodmaterial.
15. Carefully,useamatchtolightyoursample.16. Allowthelitsampletoheatthewaterinthecan.Blacksootwill
accumulateontheunderneathsideofthecan.17. Monitorthetemperatureincreasewithloggerpro.18. Stopdatacollectionafterthesampleburnsout.19. Findtheremainingmassoftheburnedsample.20. Repeatforadditionalfoodsamplesastimepermits.
LabActivity:MeasuringCaloriesinFoodLabActivity:MeasuringCaloriesinFoodDATACOLLECTIONTABLEMeasurement Sample1 Sample2 Sample3 Sample4 Sample5
Massofwater
Initialmass(foodpluspaperclip)g
InitialWatertemperature(Celsius)
FinalWaterTemperature(Celsius)
Finalmass(Foodsamplepluspaperclip)g
ΔT(oC)
Δ mass(g)
1.Calculatetheenergy(incalories)releasedbytheburningfoodsampleandabsorbedbythewater.
Q=mCpΔT
Q=heatabsorbedbythewater,m=massofwatering,Cp=1cal/goC,ΔT=changeintemperature
Q=________________calories
2.Prepareatableofyourresults.3.Determinethenumberofkilocalories(foodcalories)releasedbytheburningfoodsample.(1kilocalorie=1000calories)4.Calculatetheenergycontainedinthefoodinkilocalories/g5.Usinginformationonanutritionlabel,calculatekcal/g.(Dividecaloriesperservingbythenumberofgramsperserving).
LabActivity:MeasuringCaloriesinFoodLabActivity:MeasuringCaloriesinFood
6.Compareyourexperimentallydeterminedenergycontent(inkilocalories/g)tothecalculatedvaluefromthenutritionlabel.Calculatethepercenterrorforyourexperiment.PostlabReflection:Pleasetypeyouranswerstothefollowingquestions.1. Explainthesourcesoferrorinyourexperiment.2. Explain,intermsofenergytransferandtransformation,whatcausedthe
temperatureofthewatertochange.3. Wasalloftheenergycontainedintheburningfoodtransferredtothe
water?Ifnot,explainwhathappenedtotheenergythatwasnottransferredtothewater.
4. Howcouldyouimproveuponthedesignofthiscalorimetersothatitwouldworkbetter?
a. Drawadetailedlabeleddiagramofyourimprovedcalorimeter.b. Explainwhythisdesignisbetterthantheonethatyouused.
5. Acuriousstudentwantedtoknowifthecalorimeterwouldworkwith
differentamountsofwater.Thetablebelowshowstheresultsfromherburningfoodmaterialofthesamesizeandmass,butusingvariedamountsofwaterinthecan.Explainfromthetablebelowwhetherthecalorimetermeasuredtheenergyinthefoodmaterialproperlywhenusedwitheachamountofwater.
Experiment Massofwater(g) ΔT(oC)Sample1 200 19Sample2 100 39Sample3 50 77