Definitionofmole
Basicparticlesshouldbespecifiedwhenusingmol,whichcanbeatoms,molecules,ions,groupsofatoms,electrons,protons,neutronsandotherparticles,Oraspecificcombinationoftheseparticles.Accordingtointernationalregulations,thenumberofparticlescontainedin1molofparticlesis6.02×10²³,andthenumberofcarbonatomscontainedin0.012kg¹²C(carbon-12)isalsoequalto6.02×10²³.Therefore,onemoleofmattercontainsstructuralparticles.Thenumberofisequaltothenumberofatomscontainedin0.012kg¹²C(carbon12).
Sometimes,themassofonemoleofasubstanceiscalledthemolarmassofthesubstance,whichisrepresentedbythesymbolM,suchasM=2.02×10⁻³kgforhydrogenH2.ForasubstancewhosemassFisM,theratioofMtoμiscalledtheamountofthesubstance(alsoknownasthenumberofmoles),=Mμ.Forexample,M=4.04×10⁻³kgThenumberofmolesofhydrogenH₂=2.ThevolumeVmoccupiedbyonemoleofsubstanceiscalledthemolarvolume.Themolarvolumeofgasdependsontemperatureandpressure.Understandardconditions,theidealgasVm=22.41410L.Fmol⁻¹.Themolarvolumeofsolidandliquidsubstanceshasasmallrelationshipwithtemperatureandpressure.Thevolumeofamoleofdifferentsolidsubstancesanddifferentliquidsubstancesisdifferent.
Secundum quod praecisemensuramentum cognitionis experientiae, notum est quod 0.012 kgofacarbonatom¹²C(carbon-12) continet circiter 6.02×10²³.
Whyuse"12grams" and "carbon¹²C(carbon-12)"todefinemole?
Whydoyouhaveto12grams?Becauseitsnucleuscontainsequalnumbersofneutronsandprotons.Whycanthenumberofneutronsandprotonsbeequaltoeachotherasthereferenceatomforthenumberofmoles?Becauseaneutronhasonemorenegativeelectronandsomeradiationthanaproton,strictlyspeaking,asingleneutronhasaslightlyhighermassthanaproton[itsmassis1.6749286×10⁻²⁷kg(939.56563MeV),whichisslightlyhigherthanthemassofaproton.Large(themassoftheprotonis1.672621637(83)×10⁻²⁷kg)scientificcountingistoocomplicated],inordertofacilitatethemeasurementofthemassofothernuclei,itisnecessarytotakeanintermediatevalueoftheneutronmassandtheprotonmass(theaveragevalueistraditionalMeasurementmethods).Then¹²C(carbon-12)nucleusisthebestchoiceasareferencebenchmark,anditexistsmorecommonlyanditspropertiesarerelativelystable.Inthisway,onetwelfthofthemassofthe¹²C(carbon12)nucleusisscientificallytheclosesttothemassofaneutronorproton.
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OnNovember16,2018,theInternationalConferenceonWeightsandMeasurespassedaresolutionthat1molewillbedefinedas"theamountofmatterinasystemcontainingexactly6.02214076×10²³basicunitssuchasatomsormolecules".Atthesametime,theAvogadroconstantwasrevisedto6.02214076×10²³.
Basic notitia
Scientice, aggregati continentes 6.02×10²³ particulas inspicitur pro aunit, quod est aunit quod significat quantitatem materiae (symbolisn).
1molofcarbonelement continet 6.02×10²³ carbonatoms, et themassis12grams.
1molofelementalsulfurcontains6.02×10²³sulfuratomsandthemassis32grams.
Similarly,themassof1moleofanysubstanceisingrams,andthevalueisequaltotherelativeatomicmassorrelativemolecularmassofthatkindofatom(afixedvalue).
Theformulaweight (relativemolecularmss) aquae 18g, et themassof1mol-aquaemoleculeis18g, continens 6.02×10²³ aquaemolecularum.
Solet themassof1molsubstantiae dicitur themolarmassof substantia (symbolisM), theunitofmolarmassisgrams/mol, pronouncedas "grampermole" (symbolis" g/mol") Praenomen, themolarmassof wateris18g/mol, writtenasM(H₂O)=18g/mol.
Quid est substantia inter substantiam (m), quantitas substantia (n), et themolarmass (M) substantia?
Thatis:n=m/M,m=n×M,M=m/n
Generalformula:n(amountofmatter)=N(numberofparticles)/NA(Avogadroconstant)=m(mass)/M(molarmass)=V(gasvolume)/Vm(molarvolume:gasinSTP(standardcondition:273K(0℃)101KPa)1molgasvolumeis22.4L)=C(substanceconcentration)×V(totalvolumeofsolution)
Writingmethod:coefficiens+mol+chemicalformula(orChinesecharacters,nota:Chinesecharacters)Mustindicatewhetheritisamoleculeoranatom,etc.)
Forexample:onemoleofwatermoleculecanbewrittenas1molH₂Oor1molwatermolecule
Developmenthistory
InOctober1971,the14thInternationalConferenceonWeightsandMeasures,attendedby41countries,decidedtoaddtheseventhbasicunitoftheInternationalSystemofUnits(SI).Molarisusedtocalculatethenumberofparticles,themassofmatter,thevolumeofgas,theconcentrationofthesolution,theheatchangeofthereactionprocess,andsoon.MolecomesfromtheLatinmoles,whichoriginallymeansalotandaccumulation.
Thedefinitionofmoleinthe14thInternationalConferenceonWeightsandMeasuresin1971hasthefollowingtwoparagraphs:"Moleistheamountofsubstanceinasystem,andthenumberofbasicunitscontainedinthesystemisequalto0.012kgofcarbon-Thenumberofatomsof12isequal.""Whenusingmoles,thebasicunitshouldbespecified.Itcanbeatoms,molecules,ions,electronsandotherparticles,oraspecificcombinationoftheseparticles."Thetwoparagraphsaboveshouldberegardedasoneoverall.Thenumberofcarbonatomscontainedin0.012kgofcarbon-12nuclideistheAvogadroconstant(NA),andtheapproximatevaluemeasuredbytheexperimentisNA=6.02×10²³.Moleisdifferentfromgeneralunits.Ithastwocharacteristics:①Theobjectofmeasurementismicroscopicbasicunits,suchasmolecules,ions,etc.,anditcannotbeusedtomeasuremacroscopicsubstances.②ItusesAvogadro'snumberastheunitofmeasurement,whichisabatch,notthenumberofmolecules,atomsandotherparticles.Itcanalsobeusedtomeasurespecificcombinationsofmicroscopicparticles.Forexample,theamountofsulfuricacidismeasuredinmoles,thatis,1molofsulfuricacidcontains6.02×10²³sulfuricacidmolecules.Moleisthemostwidelyusedunitofmeasurementinchemistry.Forexample,itisusedinthecalculationofchemicalreactionequations,calculationinsolution,solutionpreparationanddilution,calculationofchemicalequilibrium,gasmolarvolume,andthermochemistry.basicunit.
Molarextinctioncoefficient,Molarabsorptioncoefficient,Molarabsorptioncoefficient
Spectrophotometryisbasedontheselectiveabsorptionofelectromagneticradiationbysubstanceswithdifferentmolecularstructures.Theestablishedmethodbelongstomolecularabsorptionspectrumanalysis.Whenlightpassesthroughthesolution,themeasuredsubstancemoleculesabsorbacertainwavelengthofmonochromaticlight,andtheintensityoftheabsorbedlightisproportionaltothedistancethelightpasses.AlthoughitisunderstoodthatBouguerhadproposedthemathematicalexpressionoftheaboverelationshipasearlyas1729,itisgenerallybelievedthatLambertfirstdiscoveredtheexpressionin1760,anditsmathematicalformis:
T=I/I0=10(-kb)
ubi I0 est intensio lucis, est intensio levis, 10(-kb) esttheindex basis, kisaconstant, bistheoptica longitudo (plerumque exprimitur).
Legis Beer'slawisequivalentto Bouguer's, sed lex Beer expressa est inter se concentus.
T=I/I0=10(-kb)
wherecistheconcentrationofthelight-absorbingsubstance(usuallyexpresseding/Lormg/Lastheunit).Aftertakingthelogarithmwiththebase10astheaboveformula,alinearexpressionisobtained:
A=-logT=-log(I/I0)=log(I0/I)=εbc
whereAistheabsorbanceandεisthemolarabsorptioncoefficientorextinctioncoefficient.
TheaboveexpressionisusuallycalledBeer'slaw.Itshowsthatwhenmonochromaticlightofaspecificwavelengthpassesthroughthesolution,theabsorbanceofthesampleisproportionaltotheconcentrationoftheabsorberinthesolutionandthedistancethelightpasses.
Whenthewavelength,solutionandtemperaturearedetermined,themolarextinctioncoefficientisdeterminedbythecharacteristicsofagivensubstance.Infact,themeasuredmolarextinctioncoefficientisalsorelatedtotheinstrumentused.Therefore,inquantitativeanalysis,themolarextinctioncoefficientofaknownsubstanceisusuallynotused,butoneormoreknownconcentrationsofthesubstancetobetestedareusedasacalibrationorworkingcurve.
Absorptioncoefficient
Themathematicalexpression of Beer'slawisA=kbc, si concentratio solutionis/L, bistheoptica pathincm, constans K dicitur absorbancecoeficiens, exprimitur a, anditsunitisliter/(g·cm) [L/(g·cm],A=kbccanbescriptum A=abc.
IntheformulaA=kbcIs1mol/L,bis1cm,thenthecoefficientkiscalledmolarabsorptioncoefficient,expressedbyε,theunitisliters/(mol·cm)[L/(mol·cm)],A=kbccanbewrittenasA=εc.Inactualwork,youcannotdirectlymeasuretheabsorbancewithahigh-concentrationsolutionsuchas1mol/L,butcalculatetheabsorbancewhendilutedtoanappropriateconcentration.Theεvalueisrelatedtofactorssuchasthewavelengthoftheincidentlightandthenatureofthesolution.TheεofNADHat260nmis15000,whichiswrittenasε260NADH = 15×10³;
Forexample,cintheformulaA=kbcisthepercentageconcentration(w/v)biscm,thentheconstantkcanbeexpressedbyE%,whichiscalledthespecificabsorptioncoefficientorthepercentageabsorptioncoefficient,A=kbccanbewrittenasA=E%bc.Whenthechemicalstructureoftheanalyteisknown,εcanbeusedForvalueanalysis,ifthechemicalstructureofthetestsubstanceisunknown,εcannotbedetermined.Atthistime,itisveryconvenienttousethespecificabsorptioncoefficienttoanalyze.a,εandEareoftenusedforroughquantitativeanalysis,mainlyforqualitativeanalysis.
Chemicaequalation
Chemicaequalationcanexpresstheratiooftheamountofthesubstancebetweenthereactantandtheproductandtheratioofthemass.
Praenomen: 2H₂+O₂=(ignite)=2H₂O
Theratio ofthecoeficientisis 2,1: 2 .
Theratioofthenumberofparticles2:1:2
Theratio oftheamount of the substance2 , 1 : 2
Massratio4:32:36
Fromtheaboveanalysis,itcanbeseenthattheratioofthecoefficientsofeachsubstanceinthechemicalequationistheratiooftheamountofsubstancesbetweenthem.UsethisTheprinciplecanbebasedonthechemicalequationtocalculatetheamountofeachsubstance.
Onetwelfthofthemassofacarbonatom(¹²C)istheinternationalbenchmarkforrelativeatomicmass(formulaweight).Itisknownthat12g¹²Ccontains6.02214076×10²³carbonatoms.ThisnumberiscalledAvogadro'snumber,soitcanalsobesaidthattheamountofasubstancecontainingseveralbasicparticlesofAvogadrois1mol.Forexample,1molofoxygencontains6.02214076×10²³oxygenmolecules,itsmassis31.9988g.1molhydrogenioncontains6.02214076×10²³hydrogenions,anditsmassis1.00794g.Inthechemicalcalculation,theapproximatevalueis6.02×10²³ .