Fuhua 2018 Prelim P2 ANS

A1 (a) E [1] (b) CandD [1] (c) AandB [1] (d) BO[1]C2 O[1] [2] (e) OxidationstateofGroup0elementsis0andhencedonotappearinthetable.[1]AtomsofGroup0elementshavestableelectronicstructure.Theseatomsdonotformbondswithatomsofotherelements/loseorgainelectronstoformions[1] [2] (f) (i) [1] (f) (ii) [2] A2 (a) 46% [1] (b) ThereactionofnitrogenandhydrogentoproduceammoniaisreversibleANDsomeofammoniaproducedwillbeconvertedbacktonitrogenandhydrogen.[1] [1] (c) Theyielddecreaseswhentheoperatingtemperatureincreases[1]Howeverwhenthetemperatureistoolow,rateofreactionistoolow[1] [2] (d) -reducethewastageoflargeamountsofpreciousrawmaterialshydrogenandnitrogen-toreducesenergy/fuelrequiredtoprocesstherawmaterialstoobtainnitrogenfromfractionaldistillationofliquefiedairorcrackingofhydrocarbonstoobtainhydrogen [2]

(e) N2 +3H2 →2NH3 No.ofmolesofhydrogen=90000000/2=45000000Noofmolesofammonia=90000000/3×2=60000[1]Theoreticalmassofammonia=60000000×17=1020000g=1.02ton[1]Actualmassofammonia=50%×1.02=0.51ton[1] [3] A3 (a) Anytwoofthefollowing-MembershavethesamegeneralformulaCn H2n O-Thereisgradualincreaseinboilingpointdowntheseries-Membershavethesamefunctionalgroup OR-CHO [2] (b) name:propanal[1]structuralformula:CH3 CH2 CHO[1] [2] (c) Mr ofmethanal=30No.ofmolesofmethanal=1/30=0.033333[i]Enthalpychangeofcombustion=0.033333×-571[i]Enthalpychangeofcombustion=-4000kJ[1]working2[i][1] [2] (d) AsthenumberofcarbonatomsinthealcoholhomologousseriesincreasesthenumberofmolesofCO2 andH2 Omoleculesproducedincreases[1]thenumberofC=OandO-Hbondsmadeincreases[1]amountofenergygivenoutinbondmakingincreases [2] (e) Thenumberandtypeofbondstobebroken(i.e.8C-H,3C-C,1C=Oand11/2O=O)andmade(i,e,8C=Oand8O-H)arethesameforboth[1]Energyabsorbedtobreakthebondsandgiveouttoformnewbondsaresame[1] [2] A4 (a) exothermic[1]Heatisgivenouttotheaqueousreactionmixture[1]causingthetemperatureofthereactionmixturetoincrease [2] (b) (i) Thefurtherapartthereactivityofmagnesiumandthemetal,thehigherthetemperaturerise. [1] (ii) temperaturerise:23°C(accept24-32°C)reason:Ironislessreactivethanzincbutmorereactivethanlead[1]Hencethetemperatureriseshouldbemorethan14°Candlessthan32°C [2] (iii) Mg(s)+Fe 2+ (aq)→Fe(s)+Mg 2+ (aq)[1]Rejectifnostatesymbols. [1] (c) Magnesiumislessreactivethancalciumandsodium[1]andhenceunabletodisplacesodiumandcalciumfromaqueoussolutionsoftheirions.[1] [2]

(d) temperaturerise:17°C(accept15-20°C)reason:HydrochloricacidismonobasicwhilesulfuricacidisdibasicHencethenumberofmolesofH+ionsinhydrochloricacidishalfthatinsulfuricacid[1]andtheamountofheatgivenoffforHClishalfthatforH2SO4.[1] [3] A5 (a) anodeprotection-anode[;]cathodicprotection-cathode[;]2[;][1] [1] (b) Metalsuchaszincismorereactivethaniron[;]actsasasacrificialmetal[;]andcorrodepreferentiallyinplaceofsteel[;]byoxidisingmorereadilytoformmetallicions3[;][2] [2] (c) (i) ThelayerofmetalactsasabarrierPreventssteelbeneathfromcomingintocontactwithwaterandoxygeninsurroundings [1] (ii) Cathodicprotectionusesreactivemetalwhichwillreactwiththecorrosiveliquids [1] (iii) Ironismorereactivethancopper[;]andwouldoxidisemorereadilybylosingelectrons,[;]hencecorrodingfaster2[;][1] [1] A6 Nameofsalt Formulaof salt Namesof compoundsusedtomakesalt Silvernitrate AgNO3 silvercarbonate/oxide/hydroxide[;]andnitricacid[;] potassiumethanoate CH3 COOK potassiumhydroxideandethanoicacid ammoniumsulfate (NH4)2 SO4 [;] sulfuricacidandaqueousammonia/aq.ammoniumcarbonate[;] zinccarbonate ZnCO3 sodiumcarbonate(oranyaqueouscarbonate)[;]andzincnitrateoranyaqueouszincsalts[;] [4]

7[;][4]5-6[;][3]3-4[;][2]1-2[;][1] B7 (a) Anythreeofthefollowing:•ElementsinMendeleev’swerearrangedinorderofincreasingatomicmasswhiletheelementsinthemodernPeriodicTableinorderofincreasingproton/atomicnumber. •TherearenonoblegasesfoundinMendeleev’sunlikethemodernPeriodicTable. •InthemodernPeriodicTablethetransitionelementsarelistedoutasaseparateblockwhileinMendeleev’sthetransitionelementsarelistedwiththemainelements •Thereareabout114elementsinthemodernPeriodicTableascomparedtoMendeleev’swithonlyaboutslightlyover60elements. •MendeleevleftgapsforelementsyettobediscoveredwhilemostofthegapsarefilledupinthemainPeriodicTable. •ExceptforGroupIIelements,thesameperiodinthemodernPeriodicTableoccursinthesamecolumninMendeleev’s. [3] (b) I[1] [1] (c) EitherF,Na,MgORCℓ,K,Ca [1] (d) Theatomicradiiofelementsdecreaseacrosstheperiod[1]Acrosstheperiod,theatomicnumberincreasesandhencetheattractionofthenucleusfortheouterelectronsincreases[1]whiletheamountofscreeningremainsthesameasthenumberofinnershellsisthesameacrosstheperiod.[1] [3] (e) Iagree.TheatomicradiusofGroupIelementsandhalogensincreasesdownthegroup.[;]Hencetheattractionfortheouterelectronincreasesdownthegroup[;]–2;[1]DownGroupI,theeasetolosetheouterelectrontofrompositiveiondecreases,ANDhencethereactivityofalkalimetalsincreasesdownthegroup.[1]DownGroupVIII,theeasetogainanadditionalelectrontofromnegativeiondecreases,ANDhencethereactivityofhalogensdecreasesdownthegroup.[1] [3] (f) Transitionelements [1] B8 (a) (i) oxygen[1]4OH - (aq)→2H2O(l)+O2(g)+4e - [1] [2]

(ii) Chlorineturnedmoistbluelitmusredandthenbleached.[1] [1] (b) Heatingisrequiredtoconcentratethesodiumhydroxidesolutioncontaminatedwithsodiumchlorideproducedbythediaphragmcell[;]Fuelsarecombustedtosupplytheheatandcarbondioxideisreleasedasproduct.[;]2;[1] [1] (c) Inthemembranecell,hydroxideionscannotpassthroughthemembraneandhencesodiumhydroxidewouldnotcomeintocontactwithchlorineproducedatanode[1]Whileinthediaphragmcell,theliquidintheleftcompartmentismaintainedhighersotheflowofliquidisalwaysfromleft/anodetoright/cathodecompartmentandpreventinganyofthesodiumhydroxidesolutionformedfindingitswaybacktowherechlorineisbeingproduced.[1] [2] (d) Theoxidationstateofchlorineincreasesfrom0inCl2to+1inNaOCl.Hencechlorineisoxidised.[1]Theoxidationstateofchlorinedecreasesfrom0inCl2to-1inNaCl.Hencechlorineisreduced.[1] [2] B9E (a) (i) OrganicCompound AqueousBromine Aqueoussodiumcarbonate PotassiumManganate(VII) A Novisiblechange Effervescenceobserved Purpleacidifiedpotassiummanganate(VII)turnedcolourless. B Novisiblechange Novisiblechange Purpleacidifiedpotassiummanganate(VII)turnedcolourless. C Novisiblechange Effervescenceobserved Novisiblechange D Reddishbrownaqueousbrominedecolourisedrapidly Novisiblechange Novisiblechange aq.bromine:CorrectdescriptionofobservationforD[1]aq.sodiumcarbonate:CorrectdescriptionofobservationforAandC[1]acidifiedpotassiummanganate(VII):CorrectdescriptionofobservationforAandB[1]Novisiblechangefortheremaining[1] [4]

(ii) [2] (b) (i) [1] (ii) Mrofrepeatunit=10249000/102<No.ofrepeatunit<60000/102480.4<Noofrepeatunits<588.2Rangeofrepeatunitsis481to588 [2] (iii) [1] B9O (a) (i) Whentheengineisidling,theairintakeislower/insufficientoxygen[;]thanwhenthecariscruising,thereisgreaterextentincompletecombustionofpetrol[;]producinggreateramountsofcarbonmonoxide Whentheengineisidling,thetemperatureintheenginecompartmentislower[;]thanwhencariscruising,rateofreactionofnitrogenandoxygenislower[;]Hencelesseroxidesofnitrogenproduced.4;[3]2-3[2]1[;] [3] (ii) Acatalystprovidesanalternativereactionpathwayofloweractivationenergy[;]Hence,moreNOandCOmoleculescollidewithenergyequivalentormorethantheactivationenergy,[;]henceincreasingthefrequencyofeffectivecollisions. 2[;][1] [3]

Athightemperature,theNOandCOmoleculeshavehigherkineticenergyandmoveaboutathigherspeeds.[;]Moremoleculesalsopossessenergyequaltoorgreaterthantheactivationenergyneededtoreact.[;]HencethereisagreaterfrequencyofeffectivecollisionsbetweenCOandNOmolecules.[;] 3[;][2] (iii) FormationNitrogenoxidescanreactwithwaterandoxygenintheatmospheretoformdilutenitricacidandfallasacidrain.[1] Effects(anyone)[1]•Acidraincanerodelimestonebuildingsandmetalstructuressuchasbridges•makesthepHoflakesandriverstoolowandhencekillaquaticlife•leachesnutrientsfromthesoilandcausesplantstowitheranddie [2] (b) VolumeofSO2 =3.4/100×2=0.068dm 3 NoofmolesofSO2 =0.068/24=0.002833[1]NoofmolesofCr2 O7 2- =0.002833/3=0.0009443Volumeofsolution=0.0009443/0.1=0.00944dm 3 [1] [2]