2023 HCI Prelim P4 QP.docx

HWACHONGINSTITUTIONC2PreliminaryExaminationHigher2 NAME CTGROUP 22S CHEMISTRYPaper4 Practical CandidatesanswerontheQuestionPaper. 9729/0424August 20232hours30minutes READTHESEINSTRUCTIONSFIRST Writeyournameandclassonalltheworkyouhandin.Givedetailsofthepracticalshiftandlaboratorywhereappropriate,intheboxesprovided.Writeindarkblueorblackpen.YoumayuseanHBpencilforanydiagramsorgraphs.Donotusestaples,paperclips,glueorcorrectionfluid. Answer allquestionsinthespacesprovidedontheQuestionPaper. Theuseofanapprovedscientificcalculatorisexpected,whereappropriate.Youmaylosemarksifyoudonotshowyourworkingorifyoudonotuseappropriateunits.QualitativeAnalysisNotesareprintedonpages19and20. Attheendoftheexamination,fastenallyourworksecurelytogether.Thenumberofmarksisgiveninbrackets[ ]attheendofeachquestionorpartquestion. Shift Laboratory For Examiner’sUse 1 /16 2 /23 3 /16 Total ______________________________________________________________________________Thisdocumentconsistsof 19printedpagesand1blankpage.

2 © HwaChongInstitution2023 9729/04/C2Prelim2023 [Turnover

3 Answer allthequestionsinthespacesprovided. DONOTWRITEINTHISMARGIN 1 Determinationof amolar enthalpychangebyanindirect method Citricacid(Mr =192)isanorganictribasicacidanditsstructureisshownbelow. Inthisquestion,theformulaforcitricacidwillbewrittenasC3 H5 O(CO2 H)3 . Citricacidreactswithsodiumhydrogencarbonatetoproducesodiumcitrate,carbondioxideandwaterasshowninequation1andequation2.Themolarenthalpychangeofreactionisdifferentdependingonwhethersolidoraqueouscitricacidisused. equation1C3 H5 O(CO2 H)3 (s)+3NaHCO3 (aq)dC3 H5 O(CO2 − Na + )3 (aq)+3CO2 (g)+3H2 O(l) ΔH1 equation2C3 H5 O(CO2 H)3 (aq)+3NaHCO3 (aq)dC3 H5 O(CO2 − Na + )3 (aq)+3CO2 (g)+3H2 O(l) ΔH2 Youwillperformanexperimenttodeterminethemolarenthalpychangeofreaction,ΔH1 ,in1(a) andplanasetofexperimentstodeterminethemolarenthalpychangeofreaction,ΔH2 ,in1(b). FA1issolidcitricacid,C3 H5 O(CO2 H)3 .FA2is1.00moldm –3 sodiumhydrogencarbonate,NaHCO3 .(Note: FA2isalsousedinquestion3.) Inthespaceprovidedonpage3,preparetablesinwhichtorecordforyourexperiment:● allweighingstoanappropriatelevelofprecision● allvaluesoftemperaturetoanappropriatelevelofprecision. (a) Determinationof themolar enthalpychangeof reaction, ΔH1 (i) Procedure 1. Weighthecappedcontainercontaining FA1.Recordthemassinyourtableonpage3.2. Placeonepolystyrenecupinsideanotherpolystyrenecupandplacebothina250cm 3 glassbeaker.Transfer50cm 3 of FA2intothepolystyrenecupusinga50cm 3 measuringcylinder.3. Placealidonthecupandinsertthethermometerthroughthelid.Stirgentlythesolutionof FA2inthecupwiththethermometer.Measureandrecordtheinitialtemperature,Ti ,of FA2.4. Open the lid and empty the container of FA 1 into the polystyrene cupcontaining FA2.(YoumayneedtotapthecappedcontainertoloosentheFA1 © HwaChongInstitution2023 9729/04/C2Prelim2023 [Turnover

4 solidbeforethetransfer).Closethelidandusethethermometertogentlystirthemixture.Measureandrecordthelowesttemperatureofthemixture,Tf .5. Reweightheemptycapp