《无机化学简明教程》课件-Chapter 5 Equilibria of Slightly Solu

1Glossarysolublea.可溶的insolublea.不溶的solubilityn.溶解度soluten.溶质dissolublea.可溶解的dissolutionn.溶解dissociatev.离解dissociationn.离解作用ioniccompounds

n.离子型化合物electrolyte电解质precipitaten.沉淀homogeneousa.均相的，均匀的heterogeneousa.异相的，不均匀的heterogeneousequilibria异相平衡theSolubility-ProductConstant溶度积常数reactionquotient

反应商2PbCl2

LeadchlorideAgClSilverchlorideAgBrSilverbromideAg2CrO4

SilverchromateAg2SSilversulfideAgNO3silvernitrate

CaSO4CalciumsulfateBaSO4BariumsulfateHClhydrochloricacidH2SO4sulphuricacidHNO3Nitricacidgramlitermolemolarmolarsolubility3Chapter5EquilibriaofSlightlySolubleIonicCompounds

Aimstosolvetwoissues:ThecharacteristicsoftheequilibriumTheshiftoftheequilibrium4AgNO3(aq)+NaCl(aq)=AgCl(s)+NaNO3(aq)5

SlightlySolubleThereisnostandardruleforthesolubilityvalue.InsolublemeansS<0.1g/100gH2O,AgCl,AgBr,AgI,BaSO4

Slightlysoluble:S=0.1~1g/100gH2O,PbCl2CaSO4,Hg2SO4etc.

SolublemeansS>1g/100gH2OIonicCompounds

arestrongelectrolyteswhichdissociatecompletelyinaqueoussolution.

61TheCharacteristicsofEquilibriaofSlightlySolubleIonicCompounds1-1.TheCharacteristics：heterogeneousequilibriaBaSO4(s)

Ba2+(aq)+SO42-(aq)Makingtheassumptionofcompletedissociation,wecanstatethatforslightlysolubleioniccompounds,equilibriumexistsbetweensolidsoluteanddissolvedions.7

1-2.

TheSolubility-ProductConstant----Ksp(溶度积常数)BaSO4(s)

Ba2+(aq)+SO42-(aq)teSSKsp=[Ba2+][SO42-]=S2GenerallyAmBn

mAn++nBm-temSnSKsp=[An+]m[Bm-]n

=[mS]m[nS]n

=mmnnSm+n81-3.ComparisonofKspandS(molarsolubility)

Table1.KspandSofsomeIonicCompoundsCompositionpatternMolecularFormulaKsp

S(mol/L)ABAgCl1.8

10-10

1.3

10-5

ABAgBr5.0

10-13

7.1

10-7

A2BAg2CrO42.0

10-12

7.9

10-5

A2BAg2S6.7

10-502.6

10-17

Formoleculeswiththesamepattern,thehigheritsKsp,thehigheritsS.Formoleculeswithdifferentpatterns,higherKspdoesn’tmeanhigherS.9Thesolubility-productKspandthemolarsolubilityS,bothexpressthesolubleabilityofacompound.Asformoleculeswiththesamepattern,thehigheritsKsp,thehigheritsS.Butformoleculeswithdifferentpatterns,higherKspdoesn’tmeanhigherS.AnotherpointisthattheKspisafunctionofthetemperature,ithasnothingtodowithions’concentrations,whileSchangeswiththeions’concentrations.10Example1:CalculatesolubilityofAgCl.Ksp=1.8

10-10(a)

In1Lwater.(b)

In0.01MHCl(c)In0.01MKNO3.

Solution:(a)AgCl(s)

Ag++Cl-teSSKsp=S2

S=

Ksp=1.3

10-5M11Example1:CalculatesolubilityofAgCl.Ksp=1.8

10-10(a)

In1Lwater.S=1.3

10-5mol/L(b)

In0.01mol/LHCl.(c)In0.01mol/LKNO3.

(b)

AgCl(s)

Ag++Cl-teSS+0.01

0.01Ksp=0.01S

S=1.8

10-8mol/L

(c)

I=0.01mol/L,lgf=-0.509

z+z-

If=0.89AgCl(s)

Ag++Cl-te0.89S0.89SKsp=(0.89S)2,S=1.46

10-5mol/L

12Example1:CalculatesolubilityofAgCl.Ksp=1.8

10-10(a)

In1Lwater.S=1.3

10-5mol/L(b)

In0.01mol/LHCl.S=1.8

10-8mol/L(c)In0.01mol/LKNO3.S=1.46

10-5mol/L

CommonIonEffectThepresenceofacommoniondecreasesthesolubilityofaslightlysolubleioniccompound.ASaltEffectisanincreaseinsolubilitycausedbythepresenceionsthatarenotcommonions.13142.

Theshiftoftheequilibrium----Predictingtheformation/dissolutionofaprecipitateQvs.KspT----Since

Hissmall;KspchangesslightlywithT;C152-1.TheLawofSolubility-Product

G=

G

+RTlnQsp=-RTlnKsp+RTlnQsp

Qsp----ion-product,whoseexpressionisidenticaltothesolubility-productexpression.

G<0,Qsp>Ksp

,netforwardreactionwilltakeplace(precipitateformsuntilsolutionissaturated).

G=0,Qsp=Ksp

,nonetchangewilltakeplace,systemisatequilibrium(solutionissaturated).

G>0,Qsp<Ksp

,netreversereactionwilltakeplace(solutionisunsaturatedandnoprecipitateforms).162-2

DissolutionofaPrecipitateTherearethreemethods:Toformweakacids/basesEg.CaCO3(s)+2H+=Ca2++CO2+H2O

ToformcomplexEg.AgCl(s)+2NH3·H2O=Ag(NH3)2++Cl-

Tocarryoutanoxidation-reductionreaction

CuS(s)+4H++2NO3-=Cu2++2NO2↑+S+2H2O17Example2:P401eg.10-15Twoormoretypesofionicequilibriaexistsimultaneously----

simultaneousequilibria

182-3.PredictingwhetheraprecipitatewillformSolution:[Ca2+]=0.30

0.100/(0.100+0.200)=0.10M[F-]=0.060

0.200/0.300=0.040MQ=[Ca2+][F-]2=0.10

0.0402=1.6

10-4>Ksp(CaF2)

CaF2willprecipitate.Example3:Acommonlaboratorymethodforpreparingaprecipitateistomixsolutionsofthecomponentions.Doesaprecipitateformwhen0.100Lof0.30MCa(NO3)2ismixedwith0.200Lof0.060MNaF?Ksp(CaF2)=3.2

10-1119SomepracticalapplicationsofsolubilityequilibriaThestandardforanionprecipitatecompletely:

c<1.0

10-6

mol/L(Quantitative)c<1.0

10-5

mol/L(Qualitative)SeparatingIonsbySelectivePrecipitate

202-4.ApplicationsofIonicEquilibriatoChemicalAnalysisSeparatingIonsbySelectivePrecipitate

21Example4:Asolutionconsistsof0.2MMgCl2and0.10MCuCl2.

Howwouldyouseparatethemetalionsastheirhydroxides?KspMg(OH)2=6.3

10-10,Ksp

Cu(OH)2=2.2

10-20.Solution:Whencopperionisfullyprecipitated,the[OH-]is:[OH-]2=Ksp

Cu(OH)2/[Cu2+]=2.2

10-20/1.0

10-6=2.2

10-14[OH-]=1.5

10-7MAtthismoment,theQofMg(OH)2is:Q=[Mg2+][OH-]2=0.2

(1.5

10-7)2=4.5

10-15

<KspMg(OH)2=6.3

10-10Thatistosay,virtuallyalltheCu2+ionwouldbeprecipitated,whiletheMg2+ionwillnotprecipitate(remaininsolution).

222.5Theconversionoftheprecipitate

Example5:BaCO3(s)+CrO42-

BaCrO4(s)+CO32-

Solution:K=[CO32-]/[CrO42-]=Ksp

BaCO3/KspBaCrO