1 stoichiomitry Alevel 考试化学课件.pptx

Relativemass1.Relativemass2.Massspectrometer

Relativeatomicmass

RelativeatomicmassRelativeatomicmass(Ar)Theaveragemassofoneatomoftheelementrelativetothemassof1/12ofcarbon-12①①Oneatomofthisisotopeisgivenarelativeisotopemassofexactly12.Relativeatomicmass(Ar)=

Relativeatomicmass

RelativeatomicmassChlorine-3575.5%Chlorine-3724.5%SoRelativeatomicmass=(75.5X35+24.5X37)/100=35.5

massspectrometer

SampleInletIonisationChamberAcceleratorSeparationUnitIondetectorAmplifierRecorderVacuumPumpElectronGunNegativelychargedplatesAnalyserUnitVariablemagneticfieldIntermediatemassparticlesLighterparticlesHeavierparticles

d.Detection–Theionsreachingthedetectorarecounted,togivetherelativeabundanceofeachisotope.a.Ionisation–Thevaporisedsampleispassedthroughanelectronbeam,fromanelectrongun,formingcationsc.Deflection–Themagneticfieldofanelectromagnetdeflectsthebeam,solighterionsaredeflectedmore.Theionspassingoutoftheelectromagnetwillbeofthesamemass.b.Acceleration–Thecationsareattractedtonegativelychargedplates,passingthroughasmallholetofocusthebeam.massspectrometer

Themassspectrumofzirconium,ZrZr=(90X51.5+91X11.2+92X17.1+94X17.4+96X2.8)/100=91.2Themassspectrumofzirconium,Zr

Relativemolecularmassrelativemolecularmass(Mr)Themassofamoleculeofthecompoundrelativetothemassofanatomofcarbon-12.Relativemolecularmass(Mr)=

e.g.magnesiumchloride,MgCl2Mg24Cl35.5SoMr(MgCl2)=24+35.5X2=95

summaryRelativeatomicmass(Ar)Relativemolecularmass(Mr)MassspectraMassspectrum

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