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) Cathodicprotectionusesreactivemetalwhichwillreactwiththecorrosiveliquid