RDC 9729 02 H2 Chemistry Practice 1 MS

Q1)(a)(i)1. Diproticreferstoanacidthatdonatesamaximumoftwoofitsprotonstootheratoms[0.5]2. Organicacidreferstoanacidthatislargelymadeof carbon, hydrogenandoxygenatoms[0.5] (ii) 1. Bondangleis90degrees[1]2. Duetoringstrainwhichforcesthebondstobe90degreesratherthan120degrees[1] (b)(i)1. Singlebondsanddoublebondshavedifferent lengths-singlebondsarelongerwhiledoublebondsareshorter[0.5]2. Increasedelectrondensityinabondmeansstronger EFOAwithnucleus,hencebondlengthdecreases[0.5] (ii) Any3arrowscorrect-[0.5]Any6arrowscorrect-[1] (iii)1. Electronscanbedelocalisedintopielectroncloudsystemacrosstheentiremolecule[0.5]2. HencealltheC-Cbondsarepartialdoublebondsandhaveapartialdoublebondlength[0.5]

(c)1. SquaricacidhasahigherpH2. Reason1:Squaricacidisdiproticwhileethanoicacidismonoprotic-twiceasmanyH+ionscanbedonatedpermoleculeofsquaricacidthanethanoicacid3. Reason2:SquaricacidhasmorehighlyENoxygenatomsthatdispersethenegativechargeontheconjugatebase,increasingitsstabilityandhenceincreasingitsacidstrength.Ethanoicacidhowever,involveselectrondonatingalkylgroupsthatintensifiesthenegativechargeontheconjugatebaseanddestabilisesit.4. Reason3:Negativechargecanbedispersedtoagreaterextentinconjugatebaseofsquaricacidbecausethepielectroncloudsystemisspreadacrossthewholemolecule,whilethatofethanoicacidisonlyspreadacrossCOO- Point1+1correctreason-1mPoint1+2correctreasons-2m (d)(i)Dicarbonate: Ethylenetetracarboxylate: Benzenehexolate: 1correctstructure-0.5m

2correctstructures-1m3correctstructures-2mPenalise0.5monce,maximumtwice,ifcandidategavetheprotonatedforminsteadofthedeprotonatedform (ii) 1. Oxidisation[0.5]2. asspeciesloseselectronsinordertoneutralisethenegativecharge[0.5]3. Moreunstableasoxygenatoms[0.5]4. Donothaveafullyfilledvalenceshell[0.5] (iii)Letzbeave.oxidationno.+k+xz-2y=-mz=(2y-m-k)/x[1][0.5]ifworkingiscorrectbutalgebraicmanipulationiswrong Q2)(i) 1. Species(ketoandenol)2. withthesamemolecularformula3. ofC3 H6 O,4. butdifferentstructuralformula-5. asketohasC=O6. butenolhasHO-C=C 4-5points:0.5m6points:1m (ii)

[1]RejectifstereoisomersdrawnwithchiralcarbonbeingtheoneattachedtoOHgroup

(iii) Compound1:C=SchangesCompound2:C=Nchanges● BODifthereis2consecutivedoublebonds,i.e.S=C=C-NHorHS-C=C=NHCompound3:C=OchangesCompound4:C=OchangesbutformsdifferentdoublebondtodifferentcarbonAcceptvariations,suchasC=SandC=Ochangesinthesamecompound. [1]percompound (iv)1. AlkenesinvolveC=C[ideaoftwosameatoms]2. Haveequalelectronegativity3. willnotbedeprotonatedeasily[0.5]perpoint (v)1. Lactam-lactim[0.5]2. Amide-imidicacid[1]3. Enol-ketone[0.5] Penalise0.5mforeveryadditionalwrongtautomerpair (v)

[0.5]forany2structurescorrect[1]forall4structurescorrect 1. AtlowpH,NH2groupisprotonatedduetohigh[H+]conc2. AspHincreases,carboxylicacidisdeprotonatedfirstasconjugatebasehighlystabilisedby2highlyENOatoms3. NH3+isthendeprotonatedtoremovethechargeaspHexceeds7vianeutralisationforstability4. OHgroupisdeprotonatedthelastbecauseithasaveryhighpKavalueasthealkoxideisdestabilisedbytheelectrondonatingalkylgroups[0.5]forany1point[1]forany3points Q3)(a)MolarconcofMg2+=(1.25+1.5)/2=1.375[0.5]MolarconcofCl-=2x(1.25/2)=1.25[0.5]Molarionicstrength=(½)(1.375)(2)^2+(½)(1.25)(1)^2=3.375OR3.38[0.5]moldm -3 [0.5] (b)(i)1. ShouldnotbeAgCNorAgBrbecauseKspismuchlowerthantheother2compounds,2. andtheyonlydissociatetogive1Ag+and1CN-orBr-ions,somolarconcentrationislower3. PbCl2dissociatestogive3ions-1Pb2+and2Cl-4. MgC2O4dissociatestogive2ions-1Mg2+and1C2O42-5. Letxbe[Pb2+],2x=[Cl-].Letybe[Mg2+]=[C2O42-]6. MolarionicstrengthofPbCl2=(½)(x)(2)^2+(½)(2x)(1)^2=3x7. MolarionicstrengthofMgC2O4=(½)(y)(2)^2+(½)(y)(2)^2=4y8. KspofPbCl2=4x^3=1.7x10 -5 9. KspofMgC2O4=y^2=8.6x10 -5 10.Bydirectcomparison,yislarger11.4y>3x

12.HencemolarionicstrengthofMgC2O4isthehighest [1]foreliminatingAgCNandAgBr[0.5]forlettingconcentrationofionsbeunknowns[1]forusingmolarionicstrengthequationcorrectly[0.5]comparingKspvalues[1]correctdeductionMax2mifspecificcalculationsused (ii) 1. Solutionsarefullysaturated[1],OR2. Temperatureofallsolutionsareequal(at25degC)[1]Rejectequalvolumeofwaterasmolarionicstrengthinvolvesconcentration,i.e.molPERvol (iii) (iv)1. FormationofsolublePbCl4-decreases[Pb2+]2. PbCl2⇋Pb2++2Cl-3. Poeshiftright4. MorePbCl2dissolvestoincreaseionicstrength5. Althoughthereisadecreaseinnumberofionsduetocomplexformation,

6. ThisisnegatedbythemuchmoresignificantincreaseinsolubilityofPbCl2 1-2points:0.5m3points:1m4-5points:1.5m6points:2m (c)(i) [1]forbellshapedcurve (ii)Saltingin1. Ionicsaltdissolvesinwatertoformmobilechargecarriers/freeions2. IonicbondbetweenthesaltionsandtheRgroupsofa.a.residues3. Decreasesintramolecularionicbonds4. Increasesfavourableinteractions/H-bondingofproteinwithwatermolecules5. Energyreleasedfromtheseinteractionsissufficienttoovercomethealreadyloweredenergyusedtobreaktheintramolecularionicbonds Saltingout6. Athighsaltconcentrations,theion-dipoleinteractionsbetweenwatermoleculesandionsbecomesignificantlystronger7. Ionsandwatermoleculesareclosertogether8. Ionsnolongerbindtoionisablegroupsoftheaminoacidresidues9. IncreasesstrengthofintramolecularionicbondsbetweenoppositelychargedRgroupsofaminoacidresidues10.Proteinclumps/becomemorecompact11.Decreasesfavourableinteractions/H-bondingofproteinwithwatermolecules12.Energyreleasedfromtheseinteractionsisinsufficienttoovercometheincreasedenergyrequiredtobreaktheintramolecularionicbonds Acceptifanyofthepointsareshownonadiagram

4-5points:0.5m6points:1m7points:1.5m8points:2m9points:2.5m10>points:3m (d)(i)Procedures:1. Dissolvesaltinabeakercontainingspecificvolumeofwater[1]2. Measuredusingapipette[0.5]3. Stirwelluntilnofurtherdissolution[0.5]4. Canbeseenbyformationofcloudysuspension[0.5]5. Filterthesolutionusingafilterfunnellinedwithfilterpaper[0.5]6. Discardresidue[0.5]7. Collectfiltrate[0.5]8. AddspecificvolumeofspecificconcentrationofNaOH(aq)intothefiltrate[0.5]9. Pourfiltrateintotheburette[0.5]10.PipettespecificvolumeofspecificconcentrationofHClintoaconicalflask[0.5]11.Indicatorismethylorange[0.5]12.Dispensethetitrantintotheconicalflask.Atendpoint(redtoorange),recordthevolumeofhydroxideused.[1] Max3m Resultsprocessing:13.FindmolesofOH-used[0.5]14.Useascalefactortodeterminenumberofmolesinoriginalsolution(x)[0.5]15.FindnumberofmolesofOH-ionsfromNaOH(aq)(y)[0.5]16.FindnumberofmolesofOH-ionscontributedbythesalt(x-y)[0.5]17.FindconcentrationofOH-ionsintheinitialsolution[0.5]18.UseKspformula(dependingonthetypeofsalt)tofindtheKspvalue[0.5] Max3m Q4)(a)(i)1. Magicnumberis184[0.5]2. Requiresmanyprotonsinanucleus,whichiselectrostaticallyunfavourableduetorepellingofprotons[0.5] (ii)

[1]forcorrectaxes+increaseatincreasingratetrendRejectifthenumberofneutronsareonthex-axis.Numberofneutronsisdependentonnumberofprotons.1. Neutronshave0charge[0.5]2. HencecanstabilisethenucleusbypreventingEFOAandhencerepulsionofpositivelychargedprotons[0.5] (b)Aisoxygen(oxygen-16)[0.5]Bislead(lead-208)[0.5] (c)(i)1. AmountoftimeittakesforconcentrationofRoentgenium-282sampletodecreasetohalftheoriginalsample(is2.2min)[1] (ii) 1. Decaysveryquickly2. Difficulttofindtherelativeabundanceofisotopes3. Artificiallysynthesisedelement 0.5mperpoint (iii)(1.3)(0.5)^n=0.1[0.5]n=3.70(3.70)(2.2)=8.14min[0.5-withunits] (d)(i) 1. Hightemperatures2. Protectedfromexternalenvironment3. Requireshighspeedofnucleifornuclearfission4. Havehighlysensitivesensorstodetectatoms