1. Complexation Titrimetry
L e c t u r e 8
Complexation Titrimetry
Associate prof . L.V. Vronska
Associate prof . M.M. Mykhalkiv

2. Outline
Complexation Titrimetry and its classification. Complexing reactions, which use in titrimetry, requirements to them.
Complexonometric titrimetry (chelatometry) and its methods.
Indicators in methods of complexonometric titrimetry.
Use of complexonometric titrimetry in pharmaceutical analysis.

3. In the method complexation titration allocate such methods:
Complexation titration is titration in which the reaction between the analyte and titrant is a complexation reaction.
In the method complexation titration allocate such methods:
Mercurimetry – titrant is solution of Hg(NO3)2
Fluoridometry – titrant is solution of NaF
Cyanidometry - titrant is solution of KCN
Complexonometry - titrant is solution of sodium edetate

4. Requirements to reactions in complexation titration
reactions between the titrant and analyte must be stoichiometricaly, quantitatively
formation constant of complex should be more than   108
reaction of formation of complex compound should proceed quickly
there should be a possibility of fixing of a point of equivalence or the end point
in the conditions of titration carrying out competing reactions should not proceed

5. In mercurimetry use formation of halide complexes of Hg (II)
In mercurimetry use formation of halide complexes of Hg (II). In the conditions of titration take place following reaction:
2Cl- + Hg2+=HgCl2
Similar reactions take place in case of determination of bromide-, iodide-, thiocyanide- and cyanide-ions; it is possible to define also salts of Hg (II).

6. Hg(NO3)2 + 2 NaCl = HgCl2 + 2 NaNO3
Mercurimetry
Titrant: secondary standard solution of Hg(NO3)2
Standardization: on primary standard solution of sodium chloride NaCl:
Hg(NO3)2 + 2 NaCl = HgCl2 + 2 NaNO3
!!!The main lack of mercurimetry – high toxicity of compounds of Mercury.

7. Na2[Fe(CN)5NO] + Hg(NO3)2 = 2NaNO3 + Hg[Fe(CN)5NO]
Mercurimetry
Indicators:
1. Solution of sodium pentacianonitrozo-ferrate (ІІІ) (sodium nitroprussidum) Na2[Fe(CN)5NO], which forms with Hg2+-ions insoluble white salt:
Na2[Fe(CN)5NO] + Hg(NO3)2 = 2NaNO3 + Hg[Fe(CN)5NO]
2. A solution of diphenylcarbazone which forms with ions Hg2+ precipitate of dark blue colour.

8. Mercurimetric determination of chloridic with sodium nitroprussidum

9. Hg2+ + 4I- = [HgI4]2- Mercurimetry
Mercurimetric determination of iodide is based on such reaction:
Hg2+ + 4I- = [HgI4]2-
In the end point we observe appearance of red precipitate:
[HgI4]2- + Hg2+ = HgI2
red precipitate

10. Mercurimetric determination of iodide

11. Mercurimetry Hg2+ + 2SCN- = Hg(SCN)2 Fe3+ + 3SCN- = Fe(SCN)3
Determination of thiocyanide SCN- - ions is based on reaction:
Hg2+ + 2SCN- = Hg(SCN)2
As indicators we use solution of Fe (III) salts
To the end point:
Fe3+ + 3SCN- = Fe(SCN)3
we observe red colour of solution
In the end point:
2Fe(SCN)3 + 3Hg(NO3)2 = 3Hg(SCN)2+2Fe(NO3)3.
red colour of solution disappears

12. Determination of mercury (ІІ) salts
Mercurimetry
Determination of mercury (ІІ) salts
Titrant – solution of potassium thiocyanide KSCN
Indicator – ions of Fe3+.
To the end point:
Hg2+ + 2SCN- = Hg(SCN)2
In the end point appears red colouring of iron (ІІІ) thiocyanide solution:
In the end point:
Fe3+ + 3SCN- = Fe(SCN)3

13. Fluoridometry Titrant: primary standard solution of NaF.
Defined ions: aluminium Al3+, zirconium ZrIV, thorium ThIV, calcium Ca2+.
We use following reactions for determination:
Al3+ + 6F- = [AlF6]3-
ZrIV + 6F- = [ZrF6]2-
ThIV + 6F- = [ThF6]2-
Ions of Са2+ we determine by back titration:
Ca2+ + 2F- (excess) = CaF2
6F- (rest) + Al3+ = [AlF6]3-

14. Fluoridometry Al3+ + HOH = AlOH2+ + H+ Indicators:
acid-base indicators (Methyl orange), as solutions have acidic reaction of medium:
Al3+ + HOH = AlOH2+ + H+
Alizarine sulfate (forms complex with zirconium ZrIV – red-violet colour, with thorium ThIV– violet)
Fluoridometry serves for definition of rather high contents of substances (0,2-0,5 mol/L). The relative error can reach 1-3 %.

15. Fluoridometric determination of aluminium with Methyl orange

16. Fluoridometric determination of aluminium with Alizarine (ammoniac medium)

17. Cyanidometry Ag+ + 2CN- = [Ag(CN)2]- [Ag(CN)2]- + Ag+ = 2AgCN
Titrant: secondary standard solution of potassium cyanide KCN
Standardization: on standard solution of AgNO3:
Ag+ + 2CN- = [Ag(CN)2]-
[Ag(CN)2]- + Ag+ = 2AgCN
in the end point appears turbidity
Defined substances: heavy metals, which form stable cyanidic complexes of specific structure, for example, [Ni(CN)4]2- , [Co(CN)4]3-, [Zn(CN)4]2-.

18. [Ni(NH3)4]2+ + 4CN- = [Ni(CN)4]2- + 4NH3 AgI + 2CN- = [Ag(CN)2]- + I-
Cyanidometry
The reaction of methods:
[Ni(NH3)4]2+ + 4CN- = [Ni(CN)4]2- + 4NH3
Medium: ammoniac
Indicator: suspension of silver iodide AgI.
In the end point: dissolves the precipitate of silver iodide AgI
AgI + 2CN- = [Ag(CN)2]- + I-
turbidity transparent solution
Potassium cyanide is strong toxine!

19. Chelatometry
Complexon І: nitrilotriacetic acid (tetradentate)

20. Complexon ІІ: (EDТА) ethylenediaminetetraacetic acid
Complexon ІІІ: sodium ethylenediaminetetraacetate (Na-EDТА, trylon B, chelaton) - Na2H2Y

21. Complexon ІV: cyclohexyldiaminetetraacetic acid
All metal-EDTA complexes have a 1:1 stoichiometry.
These complexes are dissolved in water.
Metal-EDTA complexes are named – metal complexonate.

22. Preference of use of complexons
Well soluble in water and some other organic solvents
The heightened stability of complexes
Reactions passed stoichiometricaly (isn’t present stepwise complexing)
Some complexons are specific reagents on specific ions of metals (selectively)
Use as masking reagents
Reaction is fast

23. Chelatometry Са2+ + H2Y2- → CaY2- + 2H+ In3+ + H2Y2- → InY- + 2H+
Titrant: 0,05 mol/L solution of sodium edetate (Na2-EDTA)
Standardization of titrant on such substances:
Zn + H2SO4  ZnSO4 + H2 (ions of Zn2+)
MgSO4 (ions of Mg2+)
CaCO3 + HCl Ca2+ + 2Cl- + H2O + CO2 (ions of Ca2+)
ZnO + HCl  Zn2+ + 2Cl- + H2O (ions of Zn2+)
Reactions of methods:
Са2+ + H2Y2- → CaY2- + 2H+
In3+ + H2Y2- → InY- + 2H+
Th4+ + H2Y2- → ThY + 2H+

24. Chelatometry Men+ + H2Y2-  MeYn-4 + 2H+ Men+ + Y4-  MeY(n-4)+
Indicators: metallochrome indicators
Common reaction of method:
Men+ + H2Y2-  MeYn-4 + 2H+
Men+ + Y4-  MeY(n-4)+
рН of medium influences on the concentration of metal-ions (hydroxycomplexes of metal form)
рН of medium influences on the concentration of Y4-

25. Conditional formation constant and her relationship with thermodynamic and real formation constant

26. Dependence of molar part edetate-ions from рН of medium
pH=1,0
α=2,110-18
pH= 7,0
α= 4,810-4
2,0
3,710-14
8,0
5,410-3
3,0
2,510-11
9,0
5,210-2
4,0
3,610-9
10,0
3,510-1
6,0
2,210-5
11,0
9,810-1

27. Conditions of chelatometric titration
high stability of metal complexonate^ formation constant βC>108.
ageing of fixed value of рН of investigate solution
use of buffer solutions (for linkage of Н+ ions, which form)
only some cations (Fе3+, In3+, Sc3+, ZnIV, ТhIV), which form stability metal-edetate complexes, are titrated in acidic medium

28. Direct chelatometry
Conditions of use:
Reaction involving the titrant and analyte must be of known stoichiometricaly, quantitatively
The titration reaction must occur rapidly
We have indicator, which it allows effectively define the end point
Is possible titrate mixture of cations, if
Defined ions: metal-cations

29. Methods of increase of selectivity of direct titration:
Regulation of pH of investigate solutions
Fе3+, Ga3+, In3+, Tl3+, Ві3+, ZrIV, ТhIV ions (if lg βС > 20) at рН~2
at рН = 5 determine ions of Аl3+, Co3+, Ni2+, Cu2+, Zn2+, Cd2+
at рН = 9 determine ions of alkaline-earth metal ions Mg2+, Ca2+ and atc.
2. Masking of interfere ions by reagents:
F-, P2O72-, CN- - anions and Н2С4Н4О6
Со(II), Ni(II), Zn(II), Cd(II) and Hg(II)-ions may be masked by cyanide-ions
3. Change of oxidation state
Fe3+-cations are masked by reduction to Fe2+-ions.

30. Back chelatometry
Conditions of use:
Is impossible to choose of indicator
The titration reaction is too slow
If at optimal value of pH of solution, defined metal-ions form precipitates of hydroxides or basic salts
For determination of anions

31. Ме1х+ + Н2Y2- ↔ Ме1Yх-4 + 2Н+ Н2Y2- + Мg2+ ↔ МgY2- + 2Н+
Back chelatometry
Additional titrants: Zn2+ or Мg2+ salts
Ме1х+ + Н2Y2- ↔ Ме1Yх-4 + 2Н+
Defined Excess
ion of titrant 1
Н2Y2- + Мg2+ ↔ МgY2- + 2Н+
Rest of Additional
titrant titrant 2

32. Back chelatometry and back determination of anions
SO Ba2+ ↔ BaSO4↓
defined ions excess
of titrant 1
Ba2+ + Н2Y2- ↔ BaY2- + 2Н+
rest of additional
titrant titrant 2

33. Indirect chelatometry or displacement chelatometry
Conditions of use:
The analytes are unstable substance
It is impossible to indicate the equivalent (end) point in direct reaction
Analyte doesn’t react with titrant
Reaction involving the titrant and analyte mustn’t be of known stoichiometry, quantitatively
Formation of very steady complexes metal-indicator
For define of anions
Defined ions: ThIV, Нg2+, РО43-, СО32- and other.

34. Indirect chelatometry or displacement chelatometry
Меn+ + МgY2- ↔ МеYn-4 + Мg2+
Defined substituent
metal
Мg Н2Y2- ↔ МgY2- + 2Н+
substituent Titrant

35. Indirect chelatometry or displacement chelatometry
РО43- + Мg2+ + NH4+↔ МgNH4РО4↓
defined precipitate of defined ions
ions
МgNH4РО4↓+Н+↔HРО42-+Мg2++NH4+
precipitate of defined ions substituent
Мg2+ + Н2Y2- ↔ МgY2- + 2Н+
substituent titrant

36. Requirement to indicators in chelatometry
Metal-ions with metallochromic indicator form complexes 1:1 stoichiometry
Coloring of indicator and coloring of MeInd- complexes should be different
MeInd-complex should be sufficiently stability
Stability of MeInd-complex should be less than stability of MeY-complex, which it is product of titration (difference in time)
MeІnd-complex should be labile
change of coloring at titration should be contrast

37. Specific Metallochromic
Metalloindicators
Specific Metallochromic
Haven’t color Have color, but
Fe3+ - salicyl-sulphonic acid (red) with metal-cations
Ві3+ - thiourea (yellow) form complexes,
which have other
color
Metallochromic indicators:
–N=N- (Eriochrome Black T, arsenazo III)
Triphenylmethane dyes
Other indicators (purpuric acid ammonium salt (murexide), diphenylthiocarbasol (dithizon), alizarine)

38. Mechanism of change of coloring of metallochromic indicators
Me Іnd  MeІnd-
blue red
MeІnd + H2Y2-  MeY2- + H2Іnd
red colorless blue

39. Colour of MeInd complex
Defined
substances
Indicator pH
Colour of indicator
Colour of MeInd complex
Са2+
Calconecarboxylic acid
pH  12
blue
Red-violet
Mg2+
Eriochrome Black T
рН6,3
6,311,6
рН11,6
red
yellow

40. Colour of MeInd complex
Defined
substances
Indicator pH
Colour of indicator
Colour of MeInd complex
Pb2+, Zn2+, Bi3+
Xylenol orange
2  рН  6,4
рН  6,4
yellow
Red-violet
red
Al3+, Zn2+
Dithizon
рН6,3
Green-blue

41. Determination of calcium by chelatometry with Calconecarboxylic acid (BP)

42. Determination of bismut by chelatometry with Xylenol orange

43. Thanks for your attention!