6.02 x 10 23 OR
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6.02 x 1023
OR
o Weuse“convenientnumbers”ineverydaysituations.
o A“convenientnumber”isacommontermtodescribethenumberofthings.
Whatisadozen?1dozen=12
Whydon’twejustsay12?
…anditdoesn’tmatterwhattheobjectsare….adozenmeans12whetheritisadozeneggs,adozenroses,oradozenuglyhats
Itisofteneasiertogroupobjectswhencountingthem
2dozen=243dozen=36
Amoleisacountingunit.Ittellsushowmanyobjectsthereare.
Apairandadozenarealsocountingunits.
Pair means 2objects
Dozen means 12objects
Mole means 6.02x1023objects
Sowhatisamole?
Sowhatisamole? Atermusedtorepresentthenumber6.02x1023
Theamountofanysubstancecontaining6.02x1023
particles
Todefineamole,chemistsmeasure12gofcarbon‐12
…andwealsocall6.02x1023Avogadro'snumber
Avogadro’snumber=6.02x1023/mol
=602000000000000000000000
AmedeoAvogadro‐Hedidn’tactuallyidentifythenumberbutitwasnamedafterhimtohonorhismanycontributionstochemistry
Sowhyisitsuchabignumber? Whatcountingunitwouldyouusefortheseobjects?
PAIR
Sowhyisitsuchabignumber? Whatcountingunitwouldyouusefortheseobjects?
DOZEN
Sowhyisitsuchabignumber? Whatcountingunitwouldyouusefortheseobjects?
Sinceatomsandmoleculesareverysmall,thequantityusedtomeasurethemneedstobeaverylargenumber
MOLE
Doadozendonuts,adozenbooksandadozenbricksweighthesame?
NO,soneitherdoamoleofdifferentatoms,ionsormolecules
Eachsamplecontains1mol(6.02x1023atoms)
12.0g carbon 32.0g sulfur 65.38g zinc
Whichelementdoyouthinkhastheheaviestatoms?
Atomicmolarmass: Anaveragemassofallisotopesinonemoleofatoms;takes
intoaccounthownaturallyoccurringtheyare
Example:1molofcarbonhascarbon‐12,carbon‐13andcarbon‐14init.Mostofthesamplewillbecarbon‐12,sotheaverageofallisotopespresentshouldbecloseto12. Infact,itis12.01g/mol
Example:Chlorinehastwoprincipleisotopes(chlorine‐35whichoccursalmost3timesmorethanchlorine‐37) 35(.78)+37(.22)=35.44 Infact,itsatomicmolarmassis35.45g/mol
Backtocarbon….
Hereisonemoleofcarbonwhichweighs12.0g Theatomicmolarmassofcarbonontheperiodictableis….
Whichmeansthereare12.01gforeverymolofcarbon
12.01 g/mol atomicmolarmassofanelement=
mass(g)ofonemoleofatomsofthatelement
Hereis65.38gramsoftheelementzinc.Howmanymolesofzincdowehave?
1 mole
.
atomicmolarmassofanelement= mass(g)ofonemoleofatomsofthatelement
0.50molx(63.55g)=31.8g1mol
Hereis0.50molesofcopper.Howmanygramsofcopperdowehave?
31.8g
Molarmass=themassofone moleofasubstance
Sonowwe’renottalkingaboutindividualelementsbutmoleculesandcompounds
I.e.Whatisthemolarmassofwater? Theformulaforwateris:
H2O,soonemoleculecontains2 hydrogenatomsand1oxygenatom
Molarmass=themassofonemoleofasubstance
AtomicmolarmassofH=1.01g/molx2=2.02g/mol
AtomicmolarmassofO=16.00g/molx1=16.00g/mol
Molarmassofwateris18.02g/mol
Molarmass Nowyoutryit…
WhatisthemolarmassofmethanolCH3OH?
C=12.01g/molx1=12.01g/mol
H=1.01g/molx4=4.04g/mol
O=16.00g/molx1=16.00g/mol
Molarmassofmethane=32.05g/mol
Chemistscreatedtheconceptofmolarmasstoconvertbetweenmassandchemicalamount
MolarMassasaConversionFactor
m n grams mol
x 1 mol x g
x x g 1 mol
MolarMassasaConversionFactor Molarmassisoftenusedasaconversionfactorbecauseitcontainstheunitsgramsandmoles.Thus,itcanbeusedtoconvertgramstomolesandmolestograms.
Example:Howmanymolesaretherein20gofcarbon? Therelationshipis1molofcarbon=12.01g
Remember:QuantitytobexConversion=Converted convertedfactorquantity
20gx1mol=1.665mol 12.01g=1.7
mol
Convertthefollowing:1)5.0molofNaOHtograms:
MolarMassofNaOH:40g/mol1mol=40g
5.0molx40g =200g 1mol
2)360gofglucosetomoles:
MolarMassofC6H12O6:180.18g/mol1mol=180.18g
360gx1mol =1.998mol 180.18g =2.0mol
Today’sassignment MoleWorksheet
Pg.57#1‐6(a‐conly)
YouwillhaveaMoleQuizintwodays!
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