Ionic Equilibria in Analytical Chemistry

762 Pages·2012·11.52 MB·English

by  Jean-Louis Burgot (auth.)

Ionic Equilibria in Analytical Chemistry
Jean-Louis Burgot
Ionic Equilibria in Analytical
Chemistry
2123
Prof.Jean-LouisBurgot
Prof.HonorairedesUniversités
France
ISBN978-1-4419-8381-7 e-ISBN978-1-4419-8382-4
DOI10.1007/978-1-4419-8382-4
SpringerNewYorkDordrechtHeidelbergLondon
LibraryofCongressControlNumber:2012932899
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Foreword
“Ionic Equilibria in Analytical Chemistry” Draft English translation of “Chimie
analytique et équilibres ionique” by Jean-Louis Burgot, professeur honoraire de
chimieanalytique.
When I started writing Ionic Equilibrium in the early 1960s [Addison-Wesley,
1964],Iwastryingtoclarifyinmymindaconfusingpartoftheanalyticalchemistry
curriculumthatIwasteaching.Ifoundthekeyinmassandchargebalances,which
were already in use in Scandinavia through the efforts of Lars Gunnar Sillén and
colleagues(seeL.GSillén,P.W.Lange,andC.OGabrielson,ProblemsinPhysical
Chemistry(translatedfromtheSwedish),NewYork:PrenticeHall,1952).
Muchlater,aftermyCarbonDioxideEquilibriawaspublished,Iwascontacted
by a group of medical scientists who were teaching mass and charge balances in
treatingtheequilibriaofphysiologicalfluids. IalsolearnedthatthemethodsIhad
been teaching were used in quantifying the dissolution of carbon dioxide in the
oceans, an important sink for the greenhouse gas produced by industrial activity.
Still more recently, the acidification of the oceans by carbon dioxide has been of
concernbecauseofitspotentialdissolutionofcalciumcarbonateskeletonsofmarine
organisms.
Jean-Louis Burgot presented an elegant version in French of the methods by
whichequilibriainaqueoussolutionsarecalculated,butithadyettobebroughtto
an English-speaking audience. His special sections on various analytical methods,
such as those employing ceric ion, iodine, permanganate ion, and dichromate ion,
arevaluable.Heamplifieshisdiscussionofcomplexformationwithexamplesusing
mercury,ethylenediaminetetra-aceticacid(EDTA),andotherreagentsinanalysis
ofinorganicandorganicmaterials.Followingadiscussionofthesolubilityproduct,
he presents detailed precipitation titrations using silver ion and some gravimetric
methodsbasedonthesamekindofreactions.
Thisbookpresentsthe“arithmetic”ofquantitativeanalyticalchemistry,andthe
more students are aware of this background, the more they will understand the
methodsandlimitationsofmoreautomatedmethods,aswellasthevariouscomputer
methods for calculating solution equilibria. (See Chap. 12 by David R. Cogley in
IonicEquilibriumbyJamesN.Butler,1998edition,JohnWiley&Sons,NewYork.)
v
vi Foreword
I am pleased to offer my support to a work that carries on the basic theory of
solution chemistry. Even as simple exercises for musical instruments can lead to
symphonicworks,Ihopethatstudentswholearntheelementsofsolutionchemistry
willbebetterequippedtouseitinmanypracticalapplications.
JamesN.Butler
Professoremeritus,
GordonMcKay,
Professorofappliedchemistry,
Harvardschoolofengineeringandappliedsciences
Preface
Alotofoperationsinchemicalanalysisarecarriedoutinsolution, inparticularin
aqueous solutions. Because water is both a dissociating and ionizing solvent, the
chemical reactions occurring within it are generally ionic reactions. From another
standpoint, in order to obtain valid analytical conclusions, the chemical reactions
proposedtoperformtheanalysismustbecarriedoutuntiltheirterm, thatis, until
theirequilibriumhasbeenreached.
Oneofthegreatinterestsintheanalyticalchemistrypracticedinaqueoussolu-
tions lies in the fact that it can be quasi-systematically described by mathematical
equations,whichcanbegroupedthemselvesinmathematicalsystems,systemsbe-
ing, in principle, always determined. Because they are not so easily soluble, they
induce the use of informatics or the adoption of pertinent simplifications. Without
anydoubt,adoptingpertinentsimplificationsisadifficulttaskforanybodywhohas
not thoroughly mastered the discipline. Therefore, in my opinion, it is imperative,
systematically,towritefirstalltheequationsdescribingthephenomenainsolution
thatmustbesatisfied. Next, oneorseveralsimplificationsmaybemadeaccording
totheconditionsoftheexperiment.Theresultsofthecalculationsissuingfromthe
precedingsimplificationscanthenbechallengedexperimentallyinthethirdstage.
Thismethodologyconstitutestheheartofthisbook.
Briefly, it is the fortunate balance existing between the theoretical aspects re-
sulting from the mathematical equations governing the phenomena and the purely
experimentalaspectsthatconferthegreatacademicinterestonanalyticalchemistry
inaqueoussolutions.Therefore,analyticalchemistryappearstobeasclosetopure
physicsastochemistry. Furthermore, theIUPACclassifiesanalyticalchemistryin
the realm of physical chemistry. It is one of the goals of this book to provide an
exampleofsuchanassertion.
Analyticalchemistryconsistsofstudyingthephysicalandchemicalphenomena
that are applied in chemical analysis. Hence, the two disciplines should not be
confused. However, inthisbook, numerousexamplescoming, ofcourse, fromthe
realmofchemicalanalysisaregiveninordertoillustratetheprinciplesofanalytical
chemistry that are studied. These examples are taken from the fields of inorganic
andorganicchemistriesandevenfromthatofbiochemistry.Finally,alargeplaceis
giventotheanalysisofpharmaceuticallyactiveingredients.
vii
viii Preface
I particularly want to thank Professor Maurice Bernard, honorary dean of the
facultyofsciencesofCaen,forhavingintroducedmetoandhelpedmeintothiskind
ofchemistry. IdonotforgettheveryfascinatingtimeduringwhichIworkedwith
him. I also thank my wife, Gwenola Burgot, professor of analytical chemistry in
thefacultyofpharmacyoftheUniversityofRennesI,who,ofcourse,immediately
understoodtheinterestinsuchabookandwhohasalwaysencouragedmetocontinue
thegreattaskthatwasitswriting.IstillthankGabrielGorre,holderofthesuperior
chairofphysicsintheLyceeJoliot-CurieofRennes,forhisthoroughreadingofthe
manuscript.
MygreatthanksalsogotoAndréLeGoff,whowasoneofmyEnglishteachers
inschool.HehasconsiderablyhelpedmeinthetranslationoftheFrenchversionof
thisbookintotheEnglishone.MyEnglishneededhishelp!
Finally, I also thankAnnick Simon-Malard for the diligency and devotion she
exhibitedduringthepreparationofthedifferentversionsofthisbook.
Last but not least, I dedicate this book to James Newton Butler, professor of
chemistryinthedivisionofappliedsciencesatHarvardUniversity,forthebookhe
wrotein1964entitledIonicEquilibrium,aMathematicalApproach.Mybookhas
onlythepretenseofbeingacontinuationofhismasterpieceinanalyticalchemistry.
Rennes,France Prof.Jean-LouisBurgot
May2010
Contents
PartI GeneralConsiderations
1 Solvents—CompositionofSolutions.............................. 3
1.1 Definitions ................................................ 3
1.2 MolecularSolvents ......................................... 3
1.3 SolvationofSolutesinaMolecularSolvent..................... 4
1.4 WaterasSolvent ........................................... 5
1.4.1 AbilitytoGiveHBonds............................... 5
1.4.2 HighValueofItsDipolarMoment ...................... 5
1.4.3 DissociatingPowerofWater ........................... 7
1.5 DefinitionoftheSolutionComposition ........................ 7
1.6 QuantityofaSubstance ..................................... 7
1.7 DifferentExpressionsoftheComposition ...................... 8
1.7.1 CompositionExpressedinQuantityofaSubstance:
TheMolarComposition............................... 8
1.7.2 Molality ............................................ 8
1.7.3 MolarFraction ...................................... 9
1.8 CalculationoftheMolalityandtheMolarityofaSolution
fromItsMolarFraction...................................... 9
2 ThermodynamicsandEquilibrium............................... 13
2.1 ChemicalPotential ......................................... 13
2.2 GibbsFreeEnergyChange(cid:2)G andUsefulWork
syst
AvailablefromtheProcess ................................... 16
2.3 MolarReactionGibbsFunction............................... 18
2.4 EvolvingReactionsandEquilibriumConditions................. 19
2.5 EquilibriumConditionsandMassLaw......................... 21
2.6 ChemicalPotentialsandStandardStates ....................... 24
2.7 RedoxReaction:RedoxCouples .............................. 25
2.8 BriefDescriptionofanElectrochemicalCell:
Daniell’sGalvanicCell...................................... 26
ix
x Contents
2.9 ElectromotiveForceofaGalvanicCell, CellPotentialDifference,
MaximumWorkAvailablefromaChemicalReaction, andNernst’s
Equation .................................................. 28
2.10 ElectrodePotentials......................................... 30
2.11 AdditionofFreeEnthalpiesandCalculationofStandardElectrode
PotentialsfromOtherStandardElectrodePotentials.............. 32
3 ActivitiesandActivityCoefficients ............................... 37
3.1 ChemicalEquilibrium.MassLawandSpeciesActivities.......... 37
3.2 OnthePhysicalMeaningofAnActivity........................ 37
3.3 IonicStrengthofaSolution .................................. 38
3.4 Link Between Activities and Concentrations: The Activity
Coefficients ............................................... 40
3.5 StandardStatesandActivityCoefficients ....................... 40
3.6 DifferentWaystoWritetheMassLaw ......................... 41
3.7 UsualConventionsforActivities .............................. 42
3.8 DeterminationofActivities................................... 44
3.8.1 UnchargedSolutes ................................... 44
3.8.2 ActivityofAnIon:ActivityoftheWholeElectrolyte....... 44
3.9 CalculationofActivityCoefficientsandofActivities ............. 44
3.9.1 ActivityCalculationofUnchargedSpecies ............... 44
3.9.2 CalculationofActivityCoefficientsandActivitiesofIons .. 44
3.10 JustificationofDebye-Hückel’sTheory ........................ 47
PartII AcidsandBasesEquilibria—AnalyticalApplications
4 DefinitionsofAcidsandBases:StrengthofAcidsandBases......... 51
4.1 ArrheniusDefinition ........................................ 51
4.2 Brønsted–LowryDefinition .................................. 52
4.3 InexistenceoftheProtoninSolution........................... 53
4.4 BrønstedAcidityandBasicityinWater:
NatureoftheHydratedProtoninWater ........................ 54
4.5 Nomenclature ............................................. 55
4.6 About the Equivalence of theArrhenius and BrønstedTheories in
AqueousSolutions.......................................... 55
4.7 OtherTheoriesofAcidsandBases ............................ 57
4.8 QualitativeConsiderationsConcerningtheStrength
ofAcidsandBasesinWater.................................. 57
4.9 QuantitativeConsiderationsQuantifyingtheStrengths
ofAcidsandBases:DissociationAcidConstantsK andpK ..... 58
a a
4.9.1 Acids’Strength ...................................... 58
4.9.2 Bases’Strength ...................................... 60
4.10 WaterDissociation.......................................... 60
4.11 UselessnessoftheK Notion ................................. 61
b
4.12 ABriefViewoftheConceptofpH ............................ 62
Contents xi
4.13 ThePolyacidCase.......................................... 62
4.14 DistributionDiagrams....................................... 63
4.15 MacroscopicandMicroscopicEquilibriumConstants ............ 66
4.16 PredominantSpeciesArea ................................... 68
4.17 PrevisionofAcid–BaseReactions:EquilibriumConstant
ofAcid–BaseReaction ...................................... 69
4.18 AcidityScaleinWater....................................... 70
4.19 LevelingofAcidsandBasesinWater.......................... 72
5 CalculationsofpHValuesinAqueousSolutions ................... 77
5.1 AnalyticalConcentration .................................... 77
5.2 pHofPureWater........................................... 78
5.3 CalculationofpHinSolutionsofStrongAcids .................. 78
5.3.1 GeneralRelation..................................... 78
5.3.2 SimplifiedEquations ................................. 79
5.3.3 LogarithmicDiagram................................. 80
5.4 pHinSolutionsofStrongBases .............................. 81
5.5 pHinSolutionsofSaltsofStrongAcidsandBases............... 82
5.6 Ostwald’sDilutionLaw ..................................... 82
5.7 pHinSolutionsof WeakAcids ............................... 83
5.7.1 GeneralEquationPermittingthepHCalculation .......... 83
5.7.2 pHCalculationsbyApproximations..................... 84
5.7.3 CalculationswithHägg’sDiagrams ..................... 86
5.8 pHinaWeakBaseSolution.................................. 88
5.8.1 TheBaseConcentrationIsHigh ........................ 88
5.8.2 TheBasicSolutionIsHighlyDiluted.................... 89
5.9 pHofaMixtureofStrongAcids .............................. 91
5.10 pHofaMixtureofStrongBases .............................. 92
5.11 pHofaMixtureofaStrongandaWeakAcid:
IonizationRepression ....................................... 92
5.12 pHofaMixtureofaStrongandaWeakBase ................... 93
5.13 pHofanEquimolecularMixtureofaWeakBase
andaWeakAcid ........................................... 93
5.14 pHofPolyacidandPolybaseSolutions......................... 94
5.15 pHofaMonosaltofaDiacidSolution—pHofan
AmpholyteSolution......................................... 95
5.16 pHofaSolutionofanAmino-Acid............................ 96
5.17 pHofaMixtureofTwoWeakAcids........................... 100
5.18 pHofaMixtureofaWeakAcidandaWeakBase
inAnyProportion:InterestinthePrincipalReactionConcept...... 100
5.19 pHCalculationsTakingActivitiesintoAccount.................. 104
6 BufferSolutions ............................................... 107
6.1 pHofaBufferSolutionBeforeAdditionofaStrong
AcidorBase............................................... 107
6.2 pHofaBufferSolutionAfteraProtonAddition ................. 109