ap chem. stoichiometry name lab 3 – gravimetric analysis
TRANSCRIPT
APChem. Stoichiometry Name____________________
LAB3–GRAVIMETRICANALYSISIntoday’slabyouwilldeterminetheidentityofanunknowncalciumhalide(CaX2)usingaprecipitationreaction.Bymixingasolutionofthecalciumhalidewithexcessaqueoussodiumcarbonate,calciumcarbonatecanbeprecipitated,collected,andweighedtodeterminetheidentityofthehalogenintheoriginalcalciumcompound.MATERIALS
• 2.5gsodiumcarbonate • Electronicscale• 2gunknowncalciumhalide • Weighingpaper• 40mLwater • Side-armErlenmeyer+filterpaper• Two100-mLor150-mLbeakers • PlasticBuchnerfunnel• Stirringrod • Watchglass• Centrifuge • Oven(110oCto120oC)• Smalltesttubes • Hotplate
PRE-LAB1. Doaninternetsearchforeachitembelow(resultsfromsciencelab.comarefine)andcopytheNFPAdiamondsfor
eachintoyourlabnotebook.(Youdonothavetocopyitincolor.) a. MSDSsodiumchloride b.MSDSsodiumcarbonate c.MSDScalciumcarbonate
2. Supposeyoureact8.0gofanunknowncalciumhalidewithexcesssodiumcarbonatetomakeacalciumcarbonate
precipitate.Youcollect4.0goftheprecipitate.
a. Writethebalancednetionicreactionforthereactionthatoccurs.
b. Howmanymolesofcalciumcarbonatewereproduced?
c. Whatisthemolarmass(ing/mol)oftheunknowncalciumhalide?
d. Whatistheatomicmass&identityofthehalogenintheoriginalcalciumcompound?
3. Readtheprocedurebelowandprepareadatatableinyournotebookforcollectingallmeasurements.
PROCEDURE–PART11. Setupahotplatetoasettingof4.
2. Obtaintwosmallbeakers(100-mLandor150-mL).Add~2.5gofsodiumcarbonatetoonebeakerand~2gofthe
unknowncalciumhalidetotheother.Recordtheexactmassesinyourdatatable!
3. Dissolveeachsolidin~30mLofwater.Useastirringrodtodissolveeachsolidinitsbeaker.
4. Thenpouronesolutionintotheothertomixthemandcauseaprecipitationreaction.
5. Placethisbeakerwiththesolidprecipitateonthewarmhotplateforatleasttwominutes.
6. Meanwhile,setupafiltrationapparatusasshowninthepictureabove.Weighapieceoffilterpaperandplaceitin
thefunnel.Attachthetubingtothewateraspirator,turnonthewatertocreateavacuum,andwetthefilterpaper
withasmallamountofwatertomakesurethefiltrationsetupworksandthefilterpapermakesaseal.(TIP:Place
amediumbeakerinthetroughbelowtheflowingwatertominimizesplashing.)
7. Movethebeakeroffthehotplateandallowittocooluntilsafetohandle.Thenfiltertheprecipitateusingthe
filtrationapparatus.
8. Useaspatulaorstirringrodtoliftthefilterpaperoutofthefunnelandplaceitonawatchglass.Labelthewatch
glasswithasmallpieceofmaskingtape.Drythepaperinanovenfor~10-15minutes.Meanwhilestarttrial2.
9. Weighyourdriedprecipitate+filterpaper.Thendisposeofitinatrashbin.
10. Onceyou’vecompletedtwotrials,rinseallglasswareusedintheacidwashbinatthefrontoftheclassroombefore
rinsingthemwithwaterandreturningthemtothecabinet.Besuretoremoveanymaskingtapelabels.
APChem. Stoichiometry Name____________________
PART1DATATABLE–putthisinyournotebook!
Trial1 Trial2
MassofCaX2(g)
MassofNa2CO3(g)
Massofdryfilterpaper(g)
Massoffilterpaper+CaCO3(s)(g)
PROCEDURE–PART2
1. Obtaintwosmalltesttubesandatesttuberack.Recordthemassofoneofthetesttubes.Useapenciltowrite
thismassontheopaquepartofthetesttube,orlabelitsomeotherway.(Ifthereisalreadyanumberwritten,
modifyitasneeded.)
2. Add~0.25gofsodiumcarbonatetothetesttubewiththemasswrittenonit.Recordtheexactmassofsodium
carbonateyouuse!Dissolveitinwatersothetesttubeis~1/3full.
3. Add~0.2goftheunknowncalciumhalidetotheothertesttube.Recordtheexactmassyouuse!Dissolveitin
watersothetesttubeis~1/3full.
4. Pourthecontentsofonetesttubeintotheothertocauseaprecipitationreaction.Themixtureshouldnowbein
thetesttubewiththerecordedmass.
5. Placethetesttubeinacentrifugeandcentrifugeforatleast2-3minutesseconds.
6. Removethetesttubeanddecantthesupernatantliquid.
7. Washtheprecipitatebyaddingasmallamountofwatertothesametesttube,stirringwithastirringrod,and
centrifugingagainfor90seconds.
8. Removethetesttube,decantthewater,placeitintheovenfor~10minutes,allowittocool,andrecorditsmass.
9. Cleanoutthetesttubeinthesink.Iftimepermits,repeatthisforasecondtrial.
10. Rinseallglasswareusedintheacidwashbinatthefrontoftheclassroombeforerinsingthemwithwaterand
returningthemtothecabinet.Besuretoremoveanymaskingtapelabels.
PART2DATATABLE–putthisinyournotebook!
Trial1 Trial2
MassofCaX2(g)
MassofNa2CO3(g)
Massofemptytesttube(g)
Massoftesttube+CaCO3dried(g)
CALCULATIONS&ANALYSISPart1:Usingthemassofcalciumhalideandthemassofcalciumcarbonatecollected,showthefollowingforeachtrial:
1. Howmanymolesofcalciumcarbonatewereproduced?
2. Whatisthemolarmassoftheunknowncalciumhalide?
3. Whatistheatomicmass&identityofthehalogenintheoriginalcalciumcompound?
Part2:Usingthemassofcalciumhalideandthemassofcalciumcarbonatecollected,showthefollowingforeachtrial:4. Howmanymolesofcalciumcarbonatewereproduced?
5. Whatisthemolarmassoftheunknowncalciumhalide?