L e c t u r e 8

1. Lecture8 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. 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 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. 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. Mercurimetry Indicators: • 1. Solution of sodium pentacianonitrozo-ferrate (ІІІ) (sodiumnitroprussidum) Na2[Fe(CN)5NO], which forms with Hg2+-ions insolublewhite 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. Mercurimetry • Mercurimetric determination ofiodide isbased on suchreaction: Hg2+ + 4I- = [HgI4]2- Inthe end point we observeappearance of red precipitate: [HgI4]2- + Hg2+ = HgI2 red precipitate

10. Mercurimetric determination of iodide

11. Mercurimetry • 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. Mercurimetry Determination ofmercury (ІІ) salts • Titrant – solution of potassium thiocyanideKSCN • Indicator – ions of Fe3+. • To the end point: Hg2+ + 2SCN- = Hg(SCN)2 In the end point appearsred colouring ofiron (ІІІ) thiocyanide solution: • In theend 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 Indicators: • acid-base indicators (Methyl orange), as solutions have acidic reaction of medium: Al3+ + HOH = AlOH2+ + H+ • Alizarinesulfate (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 • 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. 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:nitrilotriaceticacid (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 a1:1 stoichiometry. • These complexes are dissolved in water. • Metal-EDTA complexes are named – metal complexonate.

22. Preferenceof useof 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 • Titrant: 0,05 mol/Lsolution ofsodium 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 • 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

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

28. Directchelatometry 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 itallowseffectively 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, ТhIVions (if lg βС > 20) at рН~2 • at рН =5determine ions of Аl3+, Co3+, Ni2+, Cu2+, Zn2+, Cd2+ • at рН = 9determine ions of alkaline-earth metal ionsMg2+, 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)-ionsmay bemaskedby 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-ionsformprecipitates ofhydroxidesorbasic salts • For determination of anions

31. Back chelatometry Additional titrants:Zn2+orМg2+ salts Ме1х+ + Н2Y2- ↔ Ме1Yх-4 + 2Н+ Defined Excess ion of titrant 1 Н2Y2- + Мg2+ ↔ МgY2- + 2Н+ Rest ofAdditional titrant 1 titrant 2

32. Back chelatometry and back determination of anions SO42- + Ba2+ ↔ BaSO4↓ defined ionsexcess of titrant 1 Ba2+ + Н2Y2-↔ BaY2- + 2Н+ rest of additional titrant 1 titrant 2

33. Indirect chelatometryor 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 chelatometryor displacement chelatometry Меn+ + МgY2- ↔ МеYn-4 + Мg2+ Definedsubstituent metal Мg2+ + Н2Y2-↔ МgY2- + 2Н+ substituentTitrant

35. Indirect chelatometryor displacement chelatometry РО43- + Мg2+ + NH4+↔ МgNH4РО4↓ definedprecipitate of defined ions ions МgNH4РО4↓+Н+↔HРО42-+Мg2++NH4+ precipitate of defined ionssubstituent Мg2+ + Н2Y2- ↔ МgY2- + 2Н+ substituenttitrant

36. Requirement toindicatorsin chelatometry • Metal-ions with metallochromic indicator form complexes 1:1stoichiometry • 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 10-100 time) • MeІnd-complex should be labile • change of coloring at titration should be contrast

37. Metalloindicators SpecificMetallochromic Haven’t colorHave color, but Fe3+ - salicyl-sulphonic acid (red)with metal-cations Ві3+ - thiourea (yellow)form complexes, which have other color Metallochromicindicators: • –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 Me2+ + ІndMeІnd- bluered MeІnd + H2Y2-  MeY2- + H2Іnd redcolorless blue

41. Determination of calcium by chelatometrywithCalconecarboxylic acid (BP)

42. Determination of bismut by chelatometry with Xylenol orange

43. Thanks for your attention!