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Complexation Titrimetry

Associate profAssociate prof . L.V. Vronska. L.V. VronskaAssociate profAssociate prof . M.M. Mykhalkiv

OutlineOutline

Complexation Titrimetry and its and its classification. Complexing reactions, which classification. Complexing reactions, which use in titrimetry, requirements to them.use in titrimetry, requirements to them.

Complexonometric titrimetry (chelatometryComplexonometric titrimetry (chelatometry)) and its methods.and its methods.

Indicators in methods of complexonometric Indicators in methods of complexonometric titrimetry.titrimetry.

Use of complexonometric titrimetry in Use of complexonometric titrimetry in pharmaceutical analysis.pharmaceutical analysis.

Complexation titration is titration in which the reaction between the analyte and titrant is a complexation reaction.

In the method In the method complexation titration allocate allocate such methods:such methods:

MercurimetryMercurimetry – titrant is solution of Hg(NO – titrant is solution of Hg(NO33))22

FluoridometryFluoridometry – titrant is solution of NaF – titrant is solution of NaF CyanidometryCyanidometry - titrant is solution of KCN - titrant is solution of KCN ComplexonometryComplexonometry - titrant is solution of - titrant is solution of

sodium edetatesodium edetate

Requirements to reactions in Requirements to reactions in complexation titration

reactions between the titrant and analyte must reactions between the titrant and analyte must be be stoichiometricalystoichiometricaly, , quantitativelyquantitatively

formation constantformation constant of complex should be more of complex should be more than than 10 1088

reaction of formation of complex compound reaction of formation of complex compound should proceed should proceed quicklyquickly

there should be a possibility of there should be a possibility of fixing of a point fixing of a point of equivalence or the end pointof equivalence or the end point

in the conditions of titration carrying out in the conditions of titration carrying out competing reactions should not proceedcompeting reactions should not proceed

In mercurimetry use formation of halide In mercurimetry use formation of halide complexes of Hg (II). In the conditions of complexes of Hg (II). In the conditions of titration take place following reaction:titration take place following reaction:

2Cl2Cl- - + Hg+ Hg2+2+=HgCl=HgCl22

Similar reactions take place in case of Similar reactions take place in case of determination of bromide-, iodide-, determination of bromide-, iodide-, thiocyanide- and cyanide-ions; it is possible thiocyanide- and cyanide-ions; it is possible to define also salts of Hg (II). to define also salts of Hg (II).

MercurimetryMercurimetry TitrantTitrant:: secondary standard solution of secondary standard solution of

Hg(NOHg(NO33))22

StandardizationStandardization:: on primary on primary standard standard solution ofsolution of sodium chloride NaCl: sodium chloride NaCl:

Hg(NOHg(NO33))22 + 2 NaCl = HgCl + 2 NaCl = HgCl22 + 2 NaNO + 2 NaNO33

!!!!!!The main lackThe main lack of mercurimetry – high of mercurimetry – high toxicity of compounds of Mercury.toxicity of compounds of Mercury.

MercurimetryMercurimetryIndicatorsIndicators::

1. Solution of sodium pentacianonitrozo-1. Solution of sodium pentacianonitrozo-ferrate (ІІІ) (sodiumferrate (ІІІ) (sodium nitroprussidum) nitroprussidum) NaNa22[Fe(CN)[Fe(CN)55NO], which forms with HgNO], which forms with Hg2+2+--

ions ions insolubleinsoluble white saltwhite salt::

NaNa22[Fe(CN)[Fe(CN)55NO] + Hg(NONO] + Hg(NO33))22 = 2NaNO = 2NaNO33 + +

Hg[Fe(CN)Hg[Fe(CN)55NO]NO] 2. 2. A solution of A solution of diphenylcarbazone which diphenylcarbazone which

forms with ions Hgforms with ions Hg2+2+ precipitateprecipitate of of dark dark blueblue colour. colour.

Mercurimetric determination of chloridic with Mercurimetric determination of chloridic with sodium nitroprussidumsodium nitroprussidum

MercurimetryMercurimetry Mercurimetric determination ofMercurimetric determination of iodide isiodide is

based on suchbased on such reactionreaction::

HgHg2+ 2+ + 4+ 4II-- = [ = [HgIHgI44]]2-2-

InIn the the end pointend point we we observeobserve appearanceappearance of red of red precipitateprecipitate::

[[HgIHgI44]]2-2- + + HgHg2+2+ = = HgIHgI22 red precipitatered precipitate

Mercurimetric determination of iodideMercurimetric determination of iodide

MercurimetryMercurimetry Determination of Determination of thiocyanidethiocyanide SCN SCN-- - ions is based on - ions is based on

reactionreaction::

HgHg2+2+ + 2SCN + 2SCN- - = Hg(SCN)= Hg(SCN)22

As indicators we use solution of As indicators we use solution of FeFe (III)(III) salts salts To the end pointTo the end point::

FeFe3+3+ + 3SCN + 3SCN- - = = Fe(SCN)Fe(SCN)33

we observe we observe red colourred colour of solution of solution

In the end pointIn the end point::

22Fe(SCN)Fe(SCN)33 + 3Hg(NO + 3Hg(NO33))22 = 3Hg(SCN) = 3Hg(SCN)22+2Fe(NO+2Fe(NO33))33..

red colourred colour of solution of solution disappeardisappearss

MercurimetryMercurimetry

Determination ofDetermination of mercury mercury (ІІ)(ІІ) salts salts TitrantTitrant – – solution of potassium thiocyanidesolution of potassium thiocyanide KKSCNSCN IndicatorIndicator – – ions of ions of FeFe3+3+.. To the end pointTo the end point::

HgHg2+2+ + 2SCN + 2SCN-- = Hg(SCN) = Hg(SCN)22

In the end point In the end point appear appearss red colouring ofred colouring of ironiron (ІІІ) (ІІІ) thiocyanide solutionthiocyanide solution::

In theIn the end pointend point::

FeFe3+3+ + 3SCN + 3SCN-- = = Fe(SCN)Fe(SCN)33

FluoridometryFluoridometry TitrantTitrant:: primary standard solution of NaF. primary standard solution of NaF. Defined ionsDefined ions: : aluminium Alaluminium Al3+3+, zirconium Zr, zirconium ZrIVIV, ,

thorium Ththorium ThIVIV, calcium Ca, calcium Ca2+2+. . We use following reactions for determination: We use following reactions for determination:

AlAl3+3+ + 6F + 6F- - = [AlF= [AlF66]]3-3-

ZrZrIVIV + 6F + 6F-- = [ZrF = [ZrF66]]2-2-

ThThIVIV + 6F + 6F-- = [ThF = [ThF66]]2-2-

Ions of СаIons of Са2+2+ we determine by back titration: we determine by back titration:

CaCa2+2+ + 2 + 2FF-- ((excess)excess) = CaF= CaF22

6F6F- - (rest(rest)) + Al + Al3+3+ = [AlF = [AlF66]]3-3-

FluoridometryFluoridometry

IndicatorsIndicators:: acid-base indicatorsacid-base indicators (Methyl orange (Methyl orange)), as solutions , as solutions

have acidic reaction of medium:have acidic reaction of medium:

AlAl3+3+ + HOH = AlOH + HOH = AlOH2+2+ + H + H++

AlizarineAlizarine sulfatesulfate (forms complex with (forms complex with zirconiumzirconium Zr ZrIVIV – – red-violetred-violet colour, with colour, with thoriumthorium Th ThIVIV– – violetviolet))

FluoridometryFluoridometry serves for definition of rather high serves for definition of rather high contents of substances (0,2-0,5 mol/L). The relative contents of substances (0,2-0,5 mol/L). The relative error can reach 1-3 %.error can reach 1-3 %.

Fluoridometric determination of aluminium Fluoridometric determination of aluminium with with Methyl orangeMethyl orange

Fluoridometric determination of aluminium Fluoridometric determination of aluminium with with

AlizarineAlizarine (ammoniac medium) (ammoniac medium)

CyanidometryCyanidometry Titrant:Titrant: secondary standard solution of potassium secondary standard solution of potassium

cyanide cyanide KCNKCN StandardizationStandardization: on : on standard solution of AgNOstandard solution of AgNO33::

AgAg++ + 2CN + 2CN-- = [Ag(CN) = [Ag(CN)22]]--

[Ag(CN)[Ag(CN)22]]-- + Ag + Ag++ = 2 = 2AgCNAgCNin the end point appears in the end point appears turbidityturbidity

Defined substancesDefined substances:: heavy metals, which form stable heavy metals, which form stable cyanidic complexes of specific cyanidic complexes of specific structure, for example,structure, for example, [Ni(CN)[Ni(CN)44]]2-2- , [Co(CN) , [Co(CN)44]]3-3-, [Zn(CN), [Zn(CN)44]]2-2-. .

CyanidometryCyanidometry

The reaction of methodsThe reaction of methods::

[Ni(NH[Ni(NH33))44]]2+2+ + 4CN + 4CN-- = [Ni(CN) = [Ni(CN)44]]2-2- + 4NH + 4NH33

MediumMedium:: ammoniac ammoniac IndicatorIndicator:: suspension ofsuspension of silver iodide silver iodide AgIAgI..In the end point:In the end point: dissolves the precipitate of dissolves the precipitate of

silver iodide silver iodide AgI AgI

AgIAgI + 2 + 2CNCN-- = [Ag(CN) = [Ag(CN)22]]-- + + II--

turbidity turbidity transparent solutiontransparent solutionPotassium cyanide is strong toxine!Potassium cyanide is strong toxine!

ChelatometryChelatometry

ComplexonComplexon І І:: nitrilotriaceticnitrilotriacetic acidacid ((tetratetradentatedentate))

HOOC-CH2-NCH2-COOH

CH2-COOH

ComplexonComplexon ІІ ІІ: (: (EDEDТА)ТА) ethylenediaminetetraacetic acid

ComplexonComplexon ІІІ ІІІ:: sodium sodium ethylenediaminetetraacetate (Na-(Na-EDEDТА, ТА, trylon trylon BB, , chelatonchelaton) - Na) - Na22HH22YY

HOOC-CH2

CH2-COOH

CH2-COOH

N-CH2-CH2-NHOOC-CH2 .. ..

HOOC-CH2

CH2-COOH

CH2-COONa

N-CH2-CH2-NNaOOC-CH2 .. ..

Complexon ІVComplexon ІV:: cyclohexyl cyclohexyldiaminetetraacetic acid

All All metal-EDTAmetal-EDTA complexes have a complexes have a 1:11:1

stoichiometrystoichiometry.. These complexes are dissolved in water.These complexes are dissolved in water. Metal-EDTA complexes are named – Metal-EDTA complexes are named – metal metal

complexonatecomplexonate. .

CH2-COOH

CH2-COOH

CH2-COOH

CH2-COOH

N

N

PPreferencereference of useof use of complexonsof complexons

Well soluble in water and some other organic Well soluble in water and some other organic solventssolvents

The heightened stability of complexesThe heightened stability of complexes Reactions passed Reactions passed stoichiometricalystoichiometricaly (isn’t (isn’t

present present stepwise stepwise complexing)complexing) Some complexons are specific reagents on Some complexons are specific reagents on

specific ions of metals (selectively)specific ions of metals (selectively) Use as masking reagentsUse as masking reagents Reaction is fastReaction is fast

ChelatometryChelatometry

TitrantTitrant: 0,05 : 0,05 molmol//LL solution ofsolution of sodium edetate (Nasodium edetate (Na22--EDTA)EDTA)

Standardization of titrant on such substancesStandardization of titrant on such substances: :

1)1) Zn Zn + H+ H22SOSO44 ZnSO ZnSO44 + H + H22 (ions of Zn (ions of Zn2+2+))

2)2) MgSOMgSO44 (ions of Mg(ions of Mg2+2+))

3)3) CaCOCaCO33 + HCl + HCl Ca Ca2+2+ + 2Cl + 2Cl-- + H + H22O + COO + CO22 (ions of Ca (ions of Ca2+2+))

4)4) ZnOZnO + HCl + HCl Zn Zn2+2+ + 2Cl + 2Cl-- + H + H22OO (ions of Zn (ions of Zn2+2+))

Reactions of methodsReactions of methods: :

СаСа2+2+ + + HH22YY2-2- → CaY → CaY2-2- + 2H + 2H++

InIn3+3+ + + HH22YY2-2- → InY → InY-- + 2H + 2H++

ThTh4+4+ + + HH22YY2-2- → ThY + 2H → ThY + 2H++

ChelatometryChelatometry IndicatorsIndicators:: metallochrome indicatormetallochrome indicatorss Common reaction of methodCommon reaction of method: :

MeMen+n+ + H + H22YY2-2- MeY MeYn-4n-4 + 2H + 2H++

MeMen+n+ + Y + Y4- 4- MeY MeY(n-4)+(n-4)+

рН of medium рН of medium influences on the concentration of metal-ions influences on the concentration of metal-ions (hydroxycomplexes of metal form)(hydroxycomplexes of metal form)

рН рН of medium of medium influences on the concentration of influences on the concentration of YY4-4-

4n

)4n(

YMeMeYC

Conditional formation constant and her Conditional formation constant and her relationship with thermodynamic and relationship with thermodynamic and

real formation constantreal formation constant

4YMe

C

CC

MeY

44 YMeYMe

TC ff

4YMe

RC

DDependence of molar part edetate-ions from ependence of molar part edetate-ions from рН of mediumрН of medium

pH=pH=1,01,0 αα==2,12,11010-18-18 pH=pH= 7,0 7,0 αα== 4,8 4,81010-4-4

2,02,0 3,73,71010-14-14 8,08,0 5,45,41010-3 -3

3,03,0 2,52,51010-11-11 9,09,0 5,25,21010-2-2

4,0 4,0 3,63,61010-9-9 10,010,0 3,53,51010-1-1

6,06,0 2,22,21010-5-5 11,011,0 9,89,81010-1-1

Conditions of chelatometric titrationConditions of chelatometric titration

high stabilityhigh stability of metal complexonate^ of metal complexonate^ formation constantformation constant ββCC>10>1088..

ageing of fixed value ofageing of fixed value of рН of investigate рН of investigate solutionsolution

use of buffer use of buffer solutionssolutions (for linkage of (for linkage of НН+ + ionsions, , which form) which form)

only only some cationssome cations ( (FеFе3+3+, In, In3+3+, Sc, Sc3+3+, Zn, ZnIVIV, , ТhТhIVIV), which form stability metal-edetate ), which form stability metal-edetate complexes, are titratedcomplexes, are titrated in acidic medium in acidic medium

DirectDirect chelatometrychelatometry

ConditionConditions of uses of use:: Reaction involving the titrant and analyte must Reaction involving the titrant and analyte must

be of known be of known stoichiometricalystoichiometricaly, , quantitativelyquantitatively The titration reaction must occur The titration reaction must occur rapidlyrapidly We We have indicatorhave indicator, , which itwhich it allowsallows effectively effectively

define the end pointdefine the end point Is possible titrate mixture of cations, ifIs possible titrate mixture of cations, if

Defined ionsDefined ions:: metal-cations metal-cations

4lglgDA

Methods of increase of selectivity of direct Methods of increase of selectivity of direct titration:titration:

1.1. Regulation of pH of investigate solutionsRegulation of pH of investigate solutions FеFе3+3+, Ga, Ga3+3+, In, In3+3+, Tl, Tl3+3+, Ві, Ві3+3+, Zr, ZrIVIV, Тh, ТhIVIV ionsions ( (ifif lg β lg βСС > 20) > 20)

atat рН~ рН~22 atat рН = рН = 55 determine ions of determine ions of АlАl3+3+, Co, Co3+3+, Ni, Ni2+2+, Cu, Cu2+2+, Zn, Zn2+2+, ,

CdCd2+2+

atat рН = рН = 99 determine ions of determine ions of alkaline-earthalkaline-earth metal ions metal ions MgMg2+2+, C, Caa2+2+ and atc.and atc.

2. 2. MMaskingasking of interfere ions by reagents of interfere ions by reagents:: FF--, P, P22OO77

2-2-, CN, CN-- -- anions and anions and НН22СС44НН44ОО66

Со(II), Ni(II), Zn(II), Cd(II) Со(II), Ni(II), Zn(II), Cd(II) andand Hg(II) Hg(II)-ions-ions may bemay be maskedmasked by cyanide-ionsby cyanide-ions

3. 3. CChangehange of oxidation state of oxidation state FeFe3+3+-cations are masked by reduction to-cations are masked by reduction to Fe Fe2+2+-ions.-ions.

BBack ack chelatometrychelatometry

ConditionConditions of uses of use:: IIs impossibles impossible to to choosechoose of indicator of indicator The titration reaction is The titration reaction is too slowtoo slow If at If at optimoptimal value of pH of solutional value of pH of solution,, defined defined

metal-ionsmetal-ions formform precipitates ofprecipitates of hydroxideshydroxides oror basic saltbasic saltss

For determination of anionsFor determination of anions

BBack ack chelatometrychelatometry

Additional titrantsAdditional titrants:: ZnZn2+2+ oror МgМg2+ 2+ saltssalts

МеМе11х+х+ + Н + Н22YY2-2- ↔ Ме ↔ Ме11YYх-4х-4 + 2Н + 2Н++

Defined Defined ExcessExcess

ion ion of titrant 1of titrant 1

НН22YY2-2- + + МgМg2+2+ ↔ ↔ МgМgYY2-2- + 2 + 2НН++ Rest ofRest of AAdditionaldditional

titrant 1titrant 1 titrant 2 titrant 2

BBack ack chelatometry andchelatometry and b back ack determination of anionsdetermination of anions

SOSO442-2- + + BaBa2+2+ ↔ BaSO ↔ BaSO44↓↓

defined ionsdefined ions excessexcess

of titrant 1of titrant 1

BaBa2+2+ + + НН22YY2-2- ↔ BaY↔ BaY2-2- + 2Н + 2Н++

rest of rest of additionaladditional

titrant 1titrant 1 titrant 2 titrant 2

Indirect Indirect chelatometrychelatometry or displacement or displacement chelatometrychelatometry

Conditions of use:Conditions of use: The analytes are unstable substance The analytes are unstable substance It is impossible to indicate the equivalent (end) It is impossible to indicate the equivalent (end)

point in direct reaction point in direct reaction Analyte doesn’t react with titrantAnalyte doesn’t react with titrant Reaction involving the titrant and analyte mustn’t Reaction involving the titrant and analyte mustn’t

be of known stoichiometrybe of known stoichiometry, , quantitativelyquantitatively Formation of very steady complexes metal-indicatorFormation of very steady complexes metal-indicator For define of anionsFor define of anions

Defined ions:Defined ions: Th ThIVIV, Нg, Нg2+2+, РО, РО443-3-, СО, СО33

2-2- and and otherother..

Indirect Indirect chelatometrychelatometry or displacement or displacement chelatometrychelatometry

МеМеn+n+ + МgY + МgY2-2- ↔ МеY ↔ МеYn-4n-4 + + МgМg2+2+

DefinedDefined substituentsubstituent

metalmetal

МgМg2+2+ + + НН22YY2-2- ↔ МgY↔ МgY2-2- + 2Н + 2Н++

substituentsubstituent TitrantTitrant

Indirect Indirect chelatometrychelatometry or displacement or displacement chelatometrychelatometry

РОРО443-3- + Мg + Мg2+2+ + NH + NH44

++↔ ↔ МgМgNHNH44РОРО44↓↓defineddefined precipitateprecipitate of defined of defined ionsions

ionsions

МgМgNHNH44РОРО44↓+Н↓+Н++↔H↔HРОРО442-2-++МgМg2+2++NH+NH44

++

precipitateprecipitate of defined of defined ionsions substituentsubstituent

МgМg2+2+ + + НН22YY2-2- ↔ МgY ↔ МgY2-2- + 2Н + 2Н++

substituentsubstituent titranttitrant

RequirementRequirement to to indicatorsindicators in chelatometryin chelatometry

Metal-ions with metallochromic indicator form Metal-ions with metallochromic indicator form complexes complexes 1:11:1 stoichiometrystoichiometry

Coloring of indicator and coloring of Coloring of indicator and coloring of MeInd- MeInd- complexes should be different complexes should be different

MeInd-MeInd-complex complex should be should be sufficiently sufficiently stabilitystability Stability of Stability of MeInd-MeInd-complex complex should be should be less less

than stabilitythan stability of of MeY-complexMeY-complex, which it is , which it is product of titration (difference in 10-100 time)product of titration (difference in 10-100 time)

MeІnd-complex should be MeІnd-complex should be labilelabile change of coloring at titration should be change of coloring at titration should be

contrastcontrast

MetalloindicatorsMetalloindicators

SpecificSpecific MetallochromicMetallochromic Haven’t colorHaven’t color Have color, butHave color, but

FeFe3+3+ - salicyl-sulphonic acid - salicyl-sulphonic acid ( (redred)) with metal-cationswith metal-cations ВіВі3+3+ - thiourea - thiourea ( (yellowyellow)) form complexes,form complexes,

which have otherwhich have other colorcolor

MetallochromicMetallochromic indicators:indicators: ––N=N- (N=N- (Eriochrome Black T, arsenazo III) TriphenylTriphenylmethane methane dyesdyes Other indicatorsOther indicators (purpuric acid ammonium salt ( (purpuric acid ammonium salt (murexidemurexide), ),

diphenylthiocarbasoldiphenylthiocarbasol (dithizon) (dithizon), alizarine), alizarine)

MechanismMechanism of change of coloring of change of coloring of metallochromic indicatorsof metallochromic indicators

MeMe2+2+ + + ІndІnd MeІndMeІnd-- blueblue redred

MeІndMeІnd + H + H22YY2- 2- MeY MeY2-2- + + HH22ІndІnd redred colorless colorless blue blue

DefinedDefined

substancessubstances

IndIndicatoricator pHpH Colour ofColour of iindndicatoricator

Colour ofColour of MeIndMeInd

complexcomplex

СаСа2+2+ CalconecCalconecarboxylic arboxylic acidacid

pH pH 12 12 blueblue Red-Red-violetviolet

MgMg2+2+ Eriochrome Black T

рНрН6,36,3

6,36,311,611,6

рНрН11,6 11,6

redred

blueblue

yellowyellow

redred

DefinedDefined

substancessubstances

IndIndicatoricator pHpH Colour ofColour of iindndicatoricator

Colour ofColour of MeIndMeInd

complexcomplex

PbPb2+2+,,

ZnZn2+2+,, BiBi3+3+ XXylenol ylenol orangeorange

2 2 рН рН 6,46,4

рН рН 6,4 6,4

yellowyellow

Red-violetRed-violet

redred

AlAl3+3+, Zn, Zn2+2+ DDithizonithizon рНрН6,36,3 Green-blueGreen-blue Red-Red-violetviolet

Determination of calcium by chelatometryDetermination of calcium by chelatometry withwith Calconecarboxylic acid Calconecarboxylic acid ((BPBP))

Determination of bismut by chelatometry with Determination of bismut by chelatometry with XXylenol orangeylenol orange

Thanks for your attention!