Types of EDTA titration .

complexometric
Types of EDTA titration .

1. TYPES OF EDTA TITRATION METHODS
Mr. Hemant P. Alhat
Asst. Professor, Pharma. Chemistry,
PES Modern College of Pharmacy (for Ladies), Moshi, Pune

2. TYPES OF EDTA TITRATION
METHODS
D. B. R. A. M.
D.
B
.
R.
A.
M.

3. D
Direct
Titration
•S(metalion)tobedeterminedisbufferedtopH=10
andtitrateddirectlywiththestandardEDTAsolution.
•Itmaybenecessarytopreventprecipitationofthe
hydroxideofthemetal(orabasicsalt)bytheaddition
ofsomeauxiliarycomplexingagent,suchastartrateor
citrateortriethanolamine.
•Attheequivalencepointthemagnitudeofthe
concentrationofthemetalionbeingdetermined
decreasesabruptly.
•Thisisgenerallydeterminedbythechangeincolourof
a metal indicatororby amperometric,
spectrophotometric,orpotentiometricmethods.
•S+EDTAbufferedtopH10+titratedwithEDTA

4. Metal Ion
+
Buffered at PH 10
+
Indicator
EDTA solution
E.P.

5. B
Back
titration
•Manymetalscannottitrateddirectlyreasonsr,
•theymayprecipitatefromthesolutioninthepHrangenecessary
forthetitration,or
•theymayforminertcomplexes,or
•asuitablemetalindicatorisnotavailable.
•InsuchcasesanexcessofstandardEDTAsolutionisadded,the
resultingsolutionisbufferedtothedesiredpH,andtheexcessof
theEDTAisback-titratedwithastandardmetalionsolution;
•asolutionofzincchlorideorsulphateorofmagnesiumchloride
orsulphateisoftenusedforthispurpose.
•Theendpointisdetectedwiththeaidofthemetalindicatorwhich
respondstothezincormagnesiumionsintroducedintheback-
titration.

6. Metal ion solution
+
EDTA Excess
+
Buffered PH at 10
+
Indicator (Erichrome
black T )
ZNSO4 or MgSO4
Titrant
Sample
[Metal ion (Mn )]
Determination of Manganse
E.P.
UnreactedEDTA

7. R
Replacem
ent
titration
•AlsoknownasDisplacemnt/Substitutiontitrations.
•Itisusedformetalionsthatdonotreact(orreact
unsatisfactorily)withametalindicator,or
•ThemetalionswhichformEDTAcomplexesthatare
morestablethanthoseofothermetalssuchas
magnesiumandcalcium.
•ThemetalcationMn+tobedeterminedmaybetreated
withthemagnesiumcomplexofEDTA,whenthe
followingreactionoccurs:
•Mn++MgY2-e+Mg2+
•Theamountofmagnesiumionsetfreeisequivalentto
thecationpresentandcanbetitratedwithastandard
solutionofEDTAandasuitablemetalindicator.
•Aninterestingapplicationisthetitrationofcalcium.In
thedirecttitrationofcalciumions,solochromeblack
givesapoorendpoint;ifmagnesiumispresent,itis
displacedfromitsEDTAcomplexbycalciumandan
improvedendpointresults

8. A
Alkali metric
Method
•Whenasolutionofdisodiumethylenediaminetetraacetate,Na2H2Y,isaddedtoa
solutioncontainingmetallicions,complexesareformedwiththeliberationoftwo
equivalentsofhydrogenion:
•Thehydrogenionsthussetfreecanbetitratedwithastandardsolutionofsodium
hydroxideusinganacid-baseindicatororapotentiometricendpoint;alternatively,an
iodate-iodidemixture is addWhen a solution of disodium
ethylenediaminetetraacetate,Na2H2Y,isaddedtoasolutioncontainingmetallicions,
complexesareformedwiththeliberationoftwoequivalentsofhydrogenion:The
hydrogenionsthussetfreecanbetitratedwithastandardsolutionofsodium
hydroxideusinganacid-baseindicatororapotentiometricendpoint;alternatively,an
iodate-iodidemixtureisaddedaswellastheEDTAsolutionandtheliberatediodineis
titratedwithastandardthiosulphatesolution.Thesolutionofthemetaltobe
determinedmustbeaccuratelyneutralizedbeforetitration;thisisoftenadifficult
matteronaccountofthehydrolysisofmanysalts,andconstitutesaweakfeatureof
alkalimetrictitration.edaswellastheEDTAsolutionandtheliberatediodineistitrated
withastandardthiosulphatesolution.Thesolutionofthemetaltobedeterminedmust
beaccuratelyneutralised
•before titration; this is often a difficult matter on account of the hydrolysis of many
salts, and constitutes a weak feature of alkalimetric titration.

9. M
Miscellaneous
Method
Exchangereactionsbetweenthetetracyanonickelate(I1)ion[Ni(CN),I2-(thepotassiumsaltis
readilyprepared)andtheelementtobedetermined,wherebynickelionsaresetfree,havea
limitedapplication.Thussilverandgold,whichthemselvescannotbetitrated
complexometrically,canbedeterminedinthisway.
Thesereactionstakeplacewithsparinglysolublesilversalts,andhenceprovideamethodforthe
determinationofthehalideionsCl-,Br-,1-,andthethiocyanateionSCN-.Theanionisfirst
precipitatedasthesilversalt,thelatterdissolvedinasolutionof[Ni(CN),I2-,andtheequivalent
amountofnickeltherebysetfreeisdeterminedbyrapidtitrationwithEDTAusinganappropriate
indicator(murexide,bromopyrogallolred).Fluoridemaybedeterminedbyprecipitationaslead
chlorofluoride,theprecipitatebeingdissolvedindilutenitricacidand,afteradjustingthepH
to5-6,theleadistitratedwithEDTAusingxylenolorangeindicator.“Sulphatemaybe
determinedbyprecipitationasbariumsulphateorasleadsulphate.Theprecipitateisdissolvedin
anexcessofstandardEDTAsolution,andtheexcessofEDTAisback-titratedwithastandard
magnesiumorzincsolutionusingsolochromeblackasindicator.Phosphatemaybedetermined
byprecipitatingasMg(NH,)PO,,6H2O,dissolvingtheprecipitateindilutehydrochloricacid,
addinganexcessofstandardEDTAsolution,bufferingatpH=10,andback-titratingwith
standardmagnesiumionsolutioninthepresenceofsolochromeblack.