2025年A-Level考试《化学真题》

2025年A-Level考试《化学真题》考试时间：______分钟总分：______分姓名：______第一部分1.Definetheterm'atom'inthecontextofchemicalstructure.2.Explaintheconceptofelectronegativityandhowitinfluencesthetypeofchemicalbondformedbetweentwoatoms.3.Describetheelectronicconfigurationofanitrogenatom(N).4.Statethemaintypesofintermolecularforcespresentinliquidwater.Brieflydescribethenatureofoneoftheseforces.5.Define'Avogadro'sconstant'andstateitsvaluewiththeappropriateunit.6.Calculatethenumberofmolesofsodium(Na)presentin85.1gramsofsodiummetal,givenitsmolarmassis22.99g/mol.7.Agasoccupiesavolumeof250.0cm³atapressureof1.02atm.Calculateitsvolumeatstandardtemperatureandpressure(STP),assumingthetemperatureandamountofgasremainconstant.Giveyouranswerinlitres.8.Explainthedifferencebetween'endothermic'and'exothermic'reactionsintermsofenergychange.9.Define'activationenergy'inachemicalreaction.10.Writethebalancedchemicalequationforthecompletecombustionofpropane(C₃H₈)inoxygen(O₂).第二部分11.ExplainhowLeChatelier'sPrinciplecanbeusedtopredicttheeffectofchangingpressureonthepositionofequilibriumforareversiblereaction.Useaspecificexampletoillustrateyouranswer.12.Definetheterms'strongacid'and'weakacid'.Giveoneexampleofeach.13.CalculatethepHofa0.00150Msolutionofhydrochloricacid(HCl).AssumetheconcentrationofH⁺ionsisequaltotheconcentrationofHCl.14.Whatisa'buffersolution'?Statethepurposeofusingabuffersolutioninachemicalsystem.15.Define'rateofreaction'.Describeanexperimentalmethodtodeterminetherateofreactionforthereactionbetweensodiumthiosulfatesolutionandhydrochloricacidsolution.Includeinyouranswerthequantitiesthatwouldbemeasuredandhowtheratewouldbedeterminedovertime.16.Explainthemeaningoftheterm'reactionmechanism'.Whyisitimportanttounderstandthereactionmechanismofachemicalreaction?17.Define'chemicalequilibrium'.Ischemicalequilibriumastaticordynamicprocess?Explainyouranswer.18.Forthereaction2SO₂(g)+O₂(g)⇌2SO₃(g),theequilibriumconstant(Kc)atacertaintemperatureis4.5x10³.WriteanexpressionforKcforthisreaction.IftheequilibriumconcentrationsofSO₂andO₂are0.025Mand0.030Mrespectively,calculatetheequilibriumconcentrationofSO₃.第三部分19.Statethemainfunctionalgroupspresentinthefollowingorganiccompounds:a)Ethanol(C₂H₅OH)b)Aceticacid(CH₃COOH)c)Benzene(C₆H₆)d)Ethene(C₂H₄)20.Describethemechanismofthenucleophilicsubstitutionreaction(SN2)involvingaprimaryalkylhalide.Drawthestructureoftheproductformedwhenbromoethane(CH₃CH₂Br)reactswithhydroxideion(OH⁻)viatheSN2mechanism.21.Explaintheconceptof'isomerism'inorganicchemistry.GiveoneexampleofstructuralisomersforahydrocarbonwiththemolecularformulaC₄H₁₀.22.Whatismeantbytheterm'alkene'?Givethegeneralmolecularformulaforalkenes.23.Describethetestforidentifyingunsaturatedhydrocarbons(alkenes)usingbrominewater.Writeawordequationforthereactioninvolved.24.Statethetypeofreactionthatoccurswhenethanolistreatedwithconcentratedsulfuricacidat170°C.Givethestructureofthemainorganicproductformed.25.Define'polymerisation'.Whatisthedifferencebetweenadditionpolymerisationandcondensationpolymerisation?Giveoneexampleofapolymerformedbyeachtypeofreaction.第四部分26.DescribethetrendsinthefollowingpropertiesacrossthefirstperiodofthePeriodicTable(fromlithiumtoneon):a)Firstionisationenergyb)Atomicradiusc)Reactivitywithwater27.Namethemaingroup(family)towhichthefollowingelementsbelongandstateonecharacteristicpropertyofthatgroup:a)Sodium(Na)b)Chlorine(Cl)c)Magnesium(Mg)28.Explainwhytheionicradiusofchlorideion(Cl⁻)islargerthantheatomicradiusofchlorineatom(Cl).29.Describehowyouwouldprepareapuresampleofsodiumchloride(NaCl)fromseawater.Includethenamesofanyapparatusused.30.Whatisa'coordinationcompound'?Givetheformulaofacoordinationcompoundcontainingthehexaaquachromium(III)ion,Cr(H₂O)₆³⁺.31.Define'oxides'.Classifycarbondioxide(CO₂)andsulfurtrioxide(SO₃)asacidicoxides,basicoxides,orneutraloxides.Justifyyourclassificationforeach.32.Writeequationstoshowthereactionofsulfurdioxide(SO₂)with:a)Waterb)Oxygenc)Adilutesolutionofsodiumhydroxide(NaOH).第五部分33.StatetheLawofConservationofMass.34.Define'mole'intermsofAvogadro'sconstant.35.Astudentperformsanexperimenttodeterminetheformulaofametaloxide.Theyheat1.84gofmagnesiumpowderinexcessair.Afterthereaction,themassofthemagnesiumoxideproducedis2.52g.Calculatetheempiricalformulaofthemetaloxide.(Assumemagnesiumonlyformsmagnesiumoxide).36.Describethemaindifferencesbetweenioniccompoundsandcovalentmoleculesintermsoftheirstructure,bonding,physicalproperties(meltingpoint,boilingpoint,electricalconductivity)andsolubilityinwater.37.Explainwhatismeantby'emissivespectroscopy'.Howcanitbeusedtoidentifyelementspresentinasample?38.DescribetheprinciplebehindtheuseofapHmetertomeasurethepHofasolution.Whyisitgenerallymoreaccuratethanusingindicatorpaper?39.Whatismeantbytheterm'standardenthalpychangeofformation(ΔHf°)'?StatethevalueofΔHf°forcarbondioxide(CO₂(s)).40.Explaintheroleofthecatalystinthecontactprocessfortheindustrialproductionofsulfuricacid.试卷答案第一部分1.Anatomisthesmallestunitofanelementthatretainsthechemicalpropertiesofthatelement,consistingofanucleus(containingprotonsandneutrons)surroundedbyelectrons.2.Electronegativityisameasureofanatom'sabilitytoattractsharedelectronsinachemicalbond.Itinfluencesbondtype;atomswithalargedifferenceinelectronegativitytendtoformionicbonds,whileatomswithasmalldifferenceformcovalentbonds.3.1s²2s²2p³4.Intermolecularforcespresentinliquidwaterincludehydrogenbonds(betweenH-Omolecules)anddipole-dipoleinteractions.Hydrogenbondsareatypeofstrongdipole-dipoleattractionoccurringbetweenahydrogenatombondedtoahighlyelectronegativeatom(likeO)andanotherhighlyelectronegativeatom.5.Avogadro'sconstant(N<0xE2><0x82><0x90>)isthenumberofparticles(atoms,molecules,ionsetc.)inonemoleofasubstance,equalto6.022x10²³mol⁻¹.6.Moles=Mass/MolarMass=85.1g/22.99g/mol=3.70mol.7.UsingthecombinedgaslawPV=nRTorspecificallytherelationship(P₁V₁)/(T₁)=(P₂V₂)/(T₂)atconstantn.ConvertSTPconditionstoatmandK(1atm,273.15K).V₂=(P₁V₁T₂)/(P₂T₁)=(1.02atm*250.0cm³*273.15K)/(1.00atm*298.15K)=222.4cm³.Converttolitres:222.4cm³/1000cm³/L=0.222L.8.Anendothermicreactionabsorbsenergyfromitssurroundings,resultinginapositiveenthalpychange(ΔH>0).Anexothermicreactionreleasesenergytoitssurroundings,resultinginanegativeenthalpychange(ΔH<0).9.Activationenergyistheminimumamountofenergyrequiredforreactantparticlestocollidewithsufficientenergyandcorrectorientationtoinitiateachemicalreaction.10.C₃H₈(g)+5O₂(g)→3CO₂(g)+4H₂O(l)第二部分11.AccordingtoLeChatelier'sPrinciple,ifasystematequilibriumissubjectedtoachangeinconditions(pressure,temperature,concentration),thesystemwilladjustitselfinsuchawayastocounteractthatchange.Increasingpressurefavourablyaffectsthesideoftheequilibriumwithfewergasmolecules.Forexample,intheHaberprocess(N₂(g)+3H₂(g)⇌2NH₃(g)),increasingpressureshiftstheequilibriumpositiontotheright,favouringammoniaproduction(4molesofreactantsbecome2molesofproduct).12.Astrongacidionizescompletelyoralmostcompletelyinwater,releasingallitshydrogenions(H⁺).Example:Hydrochloricacid(HCl).Aweakacidonlypartiallyionizesinwater,establishinganequilibriumbetweentheacidanditsions.Example:Aceticacid(CH₃COOH).13.pH=-log[H⁺].[H⁺]=0.00150M(forastrongacidlikeHCl).pH=-log(0.00150)≈2.82.14.Abuffersolutionisamixturecontainingaweakacidanditsconjugatebase,oraweakbaseanditsconjugateacid.ItspurposeistoresistchangesinpHwhensmallamountsofacidorbaseareadded.15.Method:Measuretheinitialvolumeofsodiumthiosulfate(Na₂S₂O₃)solutionandaddafixedvolumeofhydrochloricacid(HCl)solutiontoaconicalflask.Recordtheinitialtime.StarttimingastheHClisaddedandstircontinuously.Stopthetimerwhenthesolutionbecomesopaque(thesulfurprecipitateforms),makingthecrossonthepaperbelowinvisible.Repeatseveraltimes.Rate=(changeinvolumeofNa₂S₂O₃added)/(timetakenforthecrosstodisappear).TheratecanbedeterminedbyplottingvolumeofHCladdedagainsttimeandfindingthegradientofthetangentataspecificpoint.16.Areactionmechanismisasequenceofindividualstepsbywhichoverallchemicalchangeoccurs.Understandingthemechanismhelpsexplaintherateofreaction,theorderofreaction,andwhycertainreactantsareconvertedintospecificproducts.17.Chemicalequilibriumisthestateinareversiblereactionwheretherateoftheforwardreactionequalstherateofthereversereaction,resultinginnonetchangeintheconcentrationsofreactantsandproductsovertime.Itisadynamicprocessbecausemoleculescontinuetoreactinbothdirections,buttheoverallconcentrationsremainconstant.18.ExpressionforKc:Kc=[SO₃]²/([SO₂]²[O₂])Kc=(2SO₂(g)+O₂(g)⇌2SO₃(g)).GivenKc=4.5x10³,[SO₂]=0.025M,[O₂]=0.030M.Weneed[SO₃].RearrangeKc=[SO₃]²/(0.025²*0.030)=4.5x10³.[SO₃]²=4.5x10³*(0.025²*0.030)=4.5x10³*(0.000625*0.030)=4.5x10³*0.00001875=0.084375.[SO₃]=√0.084375≈0.290M.第三部分19.a)Hydroxylgroup(-OH)b)Carboxylgroup(-COOH)c)Benzenering(C₆H₆)d)Doublebond(C=C)20.SN2mechanisminvolvesasinglestepwherethenucleophileattacksthecarbonatomfromtheoppositesidetotheleavinggroup,displacingitinanconcertedmanner.Product:CH₃CH₂OH(ethanol).21.Isomerismistheexistenceoftwoormorecompoundswiththesamemolecularformulabutdifferentstructuralarrangementsofatoms.Example:Butane(CH₃CH₂CH₂CH₃)andisobutane(CH₃CH(CH₃)CH₃).22.Analkeneisanunsaturatedhydrocarboncontainingatleastonecarbon-carbondoublebond(C=C).Generalformula:CₙH₂ₙ.23.Brominewater(orange/brown)decolorizeswhenreactedwithanalkene.Thereactionis:Alkene+Bromine→Diatomicalkanedibromide.Example:CH₂=CH₂+Br₂→CH₂Br-CH₂Br.24.Ethanolreactswithconcentratedsulfuricacidat170°Cviadehydrationtoformethene(analkene)andwater.CH₃CH₂OH→CH₂=CH₂+H₂O.25.Polymerisationistheprocessofjoiningmanysmallmoleculescalledmonomerstogethertoformalargemoleculecalledapolymer.Additionpolymerisationinvolvestherepeatedadditionofmonomerstothedoubleortriplebondsofunsaturatedmolecules.Condensationpolymerisationinvolvestherepeatedreactionoftwodifferentmonomerswiththeeliminationofasmallmolecule,usuallywater.Example:Addition:Polyethene(fromethene);Condensation:Polyamide(fromaminoacidunits).第四部分26.a)Firstionisationenergyincreasesacrosstheperiodfromlefttorightasatomicnumberincreases.Moreprotonsinthenucleusattracttheouterelectronsmorestrongly.b)Atomicradiusdecreasesacrosstheperiodfromlefttorightduetotheincreasingnuclearchargepullingtheelectroncloudcloser,despitetheadditionofelectronshells.c)Reactivitywithwaterforalkalimetals(Group1)increasesdownthegroup.Potassiumreactsmorevigorouslythansodium.27.a)Sodium(Na)-AlkaliMetals(Group1).Characteristicproperty:Highlyreactivemetal,formsawhiteoxidewhenheated,reactsvigorouslywithwater.b)Chlorine(Cl)-Halogens(Group7).Characteristicproperty:Greenish-yellowgas,highlytoxic,reactswithmostmetalstoformchlorides,formsacidicsolutionsinwater.c)Magnesium(Mg)-AlkalineEarthMetals(Group2).Characteristicproperty:Silvery-whitemetal,moderatelyreactive,burnswithabrightwhiteflame,formswhiteoxides.28.Thechlorideion(Cl⁻)hasmoreelectronsthanthechlorineatom(Cl),andtheseadditionalelectronsincreaseelectron-electronrepulsion,causingtheelectroncloudtoexpand.TheeffectivenuclearchargeexperiencedbytheoutermostvalenceelectronsinCl⁻isslightlylessthaninCl,resultinginalargerionicradiuscomparedtotheatomicradiusofCl.29.Process:Evaporateseawaterinaseriesofevaporatingdishesorcrystallizers.Impuritieswithhigherboilingpointsremainbehind.CollectthepurifiedNaClcrystals.Apparatus:Evaporatingdishes,heatsource(Bunsenburner,hotplate),filterpaper,funnel(optionalforinitialfiltrationifneeded).30.Acoordinationcompoundisacompoundconsistingofacentralmetalionoratombondedtoanumberofsurroundingmoleculesorionscalledligands,heldtogetherbycoordinatebonds.Formula:[Cr(H₂O)₆]Cl₃(assumingthechlorideionsareoutsidethecoordinationsphere).31.Oxidesarecompoundscontainingoxygen.CO₂isanacidicoxideasitreactswithwatertoformcarbonicacid(CO₂+H₂O⇌H₂CO₃).SO₃isalsoanacidicoxideasitreactswithwatertoformsulfuricacid(SO₃+H₂O→H₂SO₄).32.a)SO₂+H₂O⇌H₂SO₃(sulfurousacid)b)2SO₂(g)+O₂(g)⇌2SO₃(g)(thermaldecompositionofSO₂toproduceSO₃,usedincontactprocess)c)SO₂+2NaOH→Na₂SO₃+H₂O(formssodiumsulfite)orSO₂+NaOH→NaHSO₃(formssodiumbisulfite)-thefirstequationismoretypicalfordiluteNaOH.第五部分33.TheLawofConservationofMassstatesthatmassisneithercreatednordestroyedinachemicalreaction.Thetotalmassofthereactantsisequaltothetotalmassoftheproducts.34.Amoleistheamountofsubstancethatcontainsasmanyelementaryentities(atoms,molecules,ions,etc.)asthereareatomsin12gramsofcarbon-12.ThisnumberisAvogadro'sconstant(N<0xE2><0x82><0x90>).35.MassofMg=1.84g.MassofMgO=2.52g.Massofoxygenreacted=2.52g-1.84g=0.68g.MolarmassofMg=24.31g/mol.MolesofMg=1.84g/24.31g/mol≈0.0759mol.MolarmassofO=16.00g/mol.MolesofO=0.68g/16.00g/mol≈0.0425mol.RatioMg:O=0.0759:0.0425≈1.79:1.Togetwholenumbers,multiplyby2:Mg:O≈3.58:2≈3:2.Empiricalformula=Mg₃O₂.(Note:MagnesiumtypicallyformsMgO.ThecalculationsuggestsMg₃O₂,whichimpliesanunusualstoichiometrynotstandardformagnesiumoxideformationinthiscontext.Thequestionlikelyexpectsthestudenttofollowthenumbersprovided).36.Ioniccompoundsconsistofionsheldtogetherbystrongelectrostaticforcesinagiantioniclattice.Covalentmoleculesconsistofatomsjoinedbysharedpairsofelectrons,oftenformingdiscretemoleculesorextendednetworks(likediamondorsilicondioxide).Physicalproperties:Ioniccompoundshavehighmelting/boilingpoints,arehard,brittle,crystallinesolids,conductelectricitywhenmoltenordissolved(ifsoluble).Covalentmoleculeshavelowmelting/boilingpoints(exceptforstrongnetworksolids),canbegases,liquids,orsoftsolids,generallydonotconductelectricity.Solubility:Ioniccompoundsoftensolubleinpolarsolventslikewater(ion-dipoleinteraction);covalentmoleculesvary,polaronessolubleinpolarsolvents,non-polaronessolubleinnon-polarsolvents.37.Emissivespectroscop