Fundamentals of Volumetric Analysis.pdf

Requirements, Advantages, Disadvantages

1. Volumetric Analysis
Dr. Jasmine Chaudhary
Associate Professor
MMCP, MM(DU), Mullana

2. Analysisinwhichcompletionofreactionisdeterminedbymeasuringvolume.
Itiscommonlyusedtodeterminetheunknownconcentrationofaknown
reactant.
Itisamethodofquantitativeanalysisinwhichonereactantofknown
concentration(standardsolution)isaddedfromtheburettetothesolutionin
conicalflaskwhoseconcentrationistobedetermineduntilarequiredreaction
iscompleted.Thepointatwhichthereactioniscompletediscalledendpoint
(equivalencepoint).Knowingthevolumeofthetitrant,concentrationofthe
unknownsubstancecanbedetermined.
Alsoknownastitrimetricanalysis.
ItwasfirstintroducedbyJeanBaptisteAndreDumas,aFrenchchemistto
determinetheproportionofnitrogencombinedwithotherelementsinorganic
compounds.

3. Advantages
Needs a simple apparatus.
Cost effective method
Precision is better than instrumental methods.
When sample is very small and only one analysis is to be performed,
simple titrations are often preferable.
Unlike instrumental methods, the equipmentsdoesn’t require constant
recaliberation.
Disadvantages
Less sensitive and less selective than instrumental methods.

4. Dependinguponthereaction,volumetrictitrationsare
furtherdividedinto4classes
AcidBaseTitration
RedoxTitration
PrecipitationTitration
ComplexometricTitrations
Whenthereactioninvolvesanacidandabase,themethod
isreferredtoasanacid-basetitration.
Whenthereactioninvolvesoxidationandreduction,the
methodisreferredtoasaredoxtitration.

5. •Acid-baseTitrations:Thestrengthofanacidcanbedetermined
usingastandardsolutionofbaseiscalledasacidimetry.Inthesame
way,thestrengthofabasecanbefoundwiththehelpofstandard
solutionofanacidisknownasalkalimetry.Theacidbasetitrationis
basedonthereactionthatneutralizationbetweenabaseoranacidic
andanalyte
•RedoxTitrations:Theredoxtitrationisalsoknownasanoxidation-
reductionreaction.Inthistypeoftitration,thechemicalreaction
takesplacewithatransferofelectronsinthereactingionsofaqueous
solutions.

6. •PrecipitationTitrations:Thetitrationisbasedontheinsoluble
precipitateformationwhenthetworeactingsubstancearebrought
intocontactarecalledasprecipitationtitration.
•ComplexometricTitrations:Thistypeoftitrationissimilarto
precipitationtitrationinthatasolidprecipitatesoutofthesample
whenareagentisadded.Thedifferenceisthatincomplexometric
titration,thesolidisformedmorequicklyandmorecompletelythan
inprecipitationtitration,whichreduceserrorsinmeasurement.
Ethylenediaminetetraaceticacid,anacidicpowderbetterknownas
EDTA,iscommonlyusedinthistypeoftitrationbecauseitreadily
bondswithmetals.

7. Terms to know
Titrate: The substance to be analyzed is called titrate.
Titrant: The reagent of known concentration which is added to
the solution of the substance to be analyzed is called titrant.
Titration Curve: A plot of solution pH versus titrant volume
during a titration.
Titration: The process of finding out the volume of the titrant
required to react completely with a known volume of solution
(Titrate) under analysis is known as titration.
Indicator: Auxiliary agents used to determine the end point of
titration. A species added to the analyte to give an observable
change at (which is the endpoint) or near the end point.

8. EndPoint(EquivalencePoint):Thepointwherethereactiongets
complete.Theendpointisthepointwherethesystemchangeswhen
themolesofthereactingtitrantexceedthemolesofthesubstance
beingtitrated.
StandardSolution:Itisasolutionofdefiniteconcentrationorof
knownstrength.
Standardization:Itisaprocesswherebytheconcentrationofa
solutionisdeterminedbytheknownconcentrationofsolution.
TitrationError:Itisthesmallestdifferencebetweenequivalence
pointandendpoint.Thisdifferenceisbecauseanindicatoralways
producesthevisualchangeeitheralittlebeforeorafterthe
equivalencepoint.

9. METHODSTODETERMINETHEENDPOINT
•pHindicator:Thisisasubstancewhichshowsthechemicalchangeby
changingthecolor.
•Apotentiometer:Thisisusedtomeasuretheelectrodepotentialofthe
solution.Theseareusedforredoxtitration.Theyshowtheendpoint
withchangingpotentialoftheworkingelectrode.
•pHmeter:Itisaion-selectiveelectrode.InpHmeterthepotentialof
electrodedependsontheamountofH+ionpresentinthesolution.The
pHofthesolutioncanbemeasuredinthewholetitration.
•Conductance:Theconductivityofsolutionsisalsochangedintitration
anditdependsontheionspresentinthesolution,mobilityofionsand
ionsconcentration.
•Colorchange:Intheredoxreactions,thecolorofsolutionchanges
withoutuseofindicator.Thisisduetodifferentoxidationstatesofthe
product.

10. ConditionsforVolumetricAnalysis
•Allapparatusshouldbecalibratedi.e.calibratingmeasuringvesselslike
volumetricflasks,pipettes,buretteisnecessary.
•Chemicalreactionmustbesimpleandshouldtakeplacequantitatively
accordingtoawelldefinedchemicalequation.
•Someindicatorstodetermineendpointshouldbeused.
•Thereshouldamarkedchangeinsomepropertiesofthesolutiontobeanalyzed
atequivalencepointlikewhenthereactioniscomplete,thereshouldbea
markedchangeineithercolorofthesolutionorsomeelectricalproperty.
•Thereactionshouldbeinstantaneous(rapid)andcomplete(99%)underthe
experimentalconditionsmaintained.
•Thereshouldbenosidereactionandifthereisformationofinterfering
substances,theseshouldberemoved.

11. FundamentalconceptsinVolumetricAnalysis
PrimaryandSecondarystandards
Preparationofstandardsolution.
Standardization
Waysofexpressingconcentration
Classificationofvolumetricmethods
Stepsinvolvedinquantitativeanalysis

12. PRIMARY AND SECONDARY STANDARD SOLUTIONS
Standardsarematerialscontainingapreciselyknownconcentrationofa
substanceforuseinquantitativeanalysis.Therearetwotypesofstandard
solutionsusedinvolumetricanalysis:PrimaryStandardandSecondary
Standard
PrimaryStandard
Intitrimetry,certainchemicalsareusedfrequentlyindefined
concentrationasreferencesolutions.Suchsubstances/chemicalsarereferredto
asprimarystandards.
Aprimarystandardisacompoundofhighpurityfromwhicha
standardsolutionispreparedbydirectweighingofquantityfollowedby
dilutiontogivedefinedvolume.

13. •Aprimarystandardisachemicalorreagentwhichhascertainpropertiessuchas
a)Itisconsideredextremelypure(highgradequality).Although0.01-0.02%
impurityistolerableifitisaccuratelyknown.
b)Theyshouldbeeasytodry,obtainandpurify.
c)Highlystable(Shouldnotreacteasily).
d)Theyshouldbeunalteredduringweighingi.e.theyshouldnotbe
hygroscopic,oxidizedbyairoraffectedbyCO2.Itshouldmaintain
unchangedcompositionduringstorage.
e)Hasveryhighmolecularweightsothattheycanbeweighedeasilyand
weighingerrorscanbenegligible.
f)Theyshouldbereadilysolubletoformstandardsolution.
g)Theyshouldbereadilyavailableandinexpensive.
h)Shouldbepreferablynontoxic

14. Examples for primary standards:
1.Acid-basetitrations:SodiumCarbonate(Anhydrous),Potassium
HydrogenPhthalate,Oxalicacid
2.Redoxtitrations:PotassiumDichromate,PotassiumBromate,
PotassiumIodate,Oxalicacid,ArsenicTrioxide
3.Precipitationtitrations:SilverNitrate
4.Complexometrictitrations:PureMetallicZincandZincChloride
SecondaryStandard
Asecondarystandardisachemicalorreagentwhichisgenerallyless
purethantheprimarystandard.

15.  Asecondarystandardsolutionisasolutioninwhichconcentrationof
dissolvedsolutehasnotbeendeterminedbyweightofcompounddissolved
butbytitrationusingprimarystandardsolution.
Examplesinclude
Sodiumhydroxide:Itisextremelyhygroscopicandabsorbmoisture
fromatmosphereso,itcannotbeusedasaprimarystandard.
Potassiumpermanganate(KMnO4):Itisagoodoxidizingagent,
reactiveandlessstable.Duetoitsreactivity,itsownoxidizedproduct
manganeseoxide(MnO2)contaminatesthecontent.That’swhyitis
unsuitableforbeingaprimarystandard.
Sodiumthiosulphate:AbsorbsCO2fromtheatmosphereandgets
decomposed.Adepositofsulphursettlesatthebottom.

16. PreparationofStandardSolutions
Standardsolutionsarepreparedbyweighingoutthedesiredamountofsolute
andthendissolvingitinappropriatesolventsusuallywaterandthenmakeup
thevolumewiththesamesolvent.
•Itismoreconvenienttopreparedilutesolutionfromconcentratedsolution
usingtherelation
M1V1(Concentrated solution)= M2V2 (Dilute solution)
Preparationof100mlof0.1MNaOHfrom1MNaOH
1x V1=0.1x100
V1= 0.1x100/1= 10ml
So10mlofconcentratedsolutioniswhendilutedwith90mlofwater,0.1M
solutionofNaOHisprepared.

17. Standardization
Todeterminetheexactconcentrationofthepreparedsolution
(secondarystandardsolution)usingprimarystandardsolutions.
e.g.Standardizationof0.1NNaOHusing0.1Noxalicacid
Standardizationof0.1NHClusing0.1Nsodiumcarbonate

18. Stepsinvolvedinquantitativevolumetricanalysis
Selectionofmethodofanalysis
Requireexperienceaswellasscientificknowledgeasthemethodselected
shouldbeaccurate,simple,preciseandeconomic.
Samplingandpreparationofsamplesolution
Sampleispowderedandrequiredamountofsampleisweighedanddissolved
insolventunderrequiredconditions.
Eliminationofinterferences
Interferingcompoundsshouldbeeliminatedfromthesolutionforappropriate
results.
CalibrationandMeasurement

19. CalibrationandMeasurement
Allapparatus,equipmentandinstrumentsneedtobecalibratedbefore
performingtheanalysisastheresultwilldependonthepropertymeasured
whichwillbeeffectiveifpropercalibrationisdone.
ObservationandCalculationofResults
Resultsobservedarethencomputedusingrequiredformulas.
Evaluationofresults

20. METHODSOFEXPRESSINGCONCENTRATION OFSOLUTION
Thesolubilityofasoluteistheamountofsolutethatwilldissolveina
givenamountofsolventatparticulartemperaturetoproduceasaturated
solution.
Solute:Asubstancedissolvedinanothersubstance,usuallythe
componentofasolutionpresentinthelesseramount.
Solvent:Asubstanceinwhichanothersubstanceisdissolved,forminga
solution.Theconcentrationofasolutionisamacroscopicproperty,
representstheamountofsolutedissolvedinaunitamountofsolventorof
solution,andcanbeexpressedinavarietyofways(qualitativelyand
quantitatively).
QualitativeExpressionsofConcentration
Semi-QuantitativeExpressionsofConcentration
QuantitativeExpressionsofConcentration

21. QualitativeExpressionsofConcentration
•Asolutioncanbequalitativelydescribedas
Dilute:Asolutionthatcontainsasmallproportionofsolute
relativetosolvent
Concentrated:Asolutionthatcontainsalargeproportionof
soluterelativetosolvent
Semi-QuantitativeExpressionsofConcentration
Asolutioncanbesemi-quantitativelydescribedas:
Unsaturated:Asolutioninwhichmoresolutecanbedissolved
Saturated:Asolutioninwhichnomoresolutecanbedissolve