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!