1. Chapter15 p 17 Complexation Reactions and Titrations CHAPTER

2. Chapter15 p Complexation reaction ( 複合反應、錯合反應 ) One of the first uses of these reactions was for the titrating cations ~ ~ the major topic Complexes are colored or absorb ultraviolet radiation ~ ~ the basis for spectrophotometric determine Complex: [adj.] 錯綜複雜的，合成的 [n] 複合物、錯合物 Complexes: 複數

3. Chapter15 p § The Formation of Complexes Complex: metal + ligand Ligand: have at least one pair of unshared electrons available for bond formation. (electron donor) Ex: H 2 O, NH 3, Cl -, Br -, I - …… ~ ~ An ion or a molecule that forms a covalent bond with a cation or neutral metal atom by donating a pair of electrons, which ate then shared by two. (p450) 449 [Cr(NH 3 ) 6 ] 3+

4. Chapter15 p § The Formation of Complexes Coordination number ( 配位數 ): the number of covalent bonds that a cation tends to form with electron donors Ex: [Cu(NH 3 ) 4 ] 2+, [CuCl 4 ] 2-, [Cr(NH 3 ) 6 ] 3+ Complexometric method: titrimetric methods based on complex formation ( 錯離子滴定法 ) Chelate ( 螯合物 ) : when a metal ion coordinates with two or more donor groups of a single ligand to form a five- or six-member heterocyclic ring. 450

5. Chapter15 p Chelate: when a metal ion coordinates with two or more donor groups of a single ligand to form a five- or six-member heterocyclic ring. ( 螯合物 ) Unidentate: ( 單牙基 ) a ligand that has a single donor group Ex: NH 3 Bidentate: ( 雙牙基 ) a ligand that has two groups available for covalent bonding Ex: glycine Tridentate, tetradentate, ……

6. Chapter15 p § The Formation of Complexes Macrocycles : metal ions and cyclic organic compounds ～～ the organic compounds contain nine or more atoms in the cycle and include at least three heteroatoms, usually O, N, S.

7. Chapter15 p The ions of alkali metals cam form complexes with crown ether and cryptand D. J. Cram, C. J. Pedersen and J.-M. Lehn Nobel prize in Chemistry in 1987

8. Chapter15 p § Complexation Equilibria 451

9. Chapter15 p

10. 451 β: the overall formation constant

11. Chapter15 p α: the fraction of the total metal or metal complex concentration existing

12. Chapter15 p Calculation of α for metal complexes 452 C T = C M = [M] + [ML] + [ML 2 ] +…… + [ML n ]

13. Chapter15 p [ML] = β 1 [M] [L] [ML 2 ] = β 2 [M] [L] 2 [ML 3 ] = β 3 [M] [L] 3 [ML n ] = β n [M] [L] n C T = C M = [M] + [ML] + [ML 2 ] +…… + [ML n ] = [M] +β 1 [M] [L]+β 2 [M] [L] 2 +...+β n [M] [L] n = [M] { 1 + β 1 [L]+β 2 [L] 2 + …...+β n [L] n }

14. Chapter15 p

15. § The Formation of Insoluble Species § Ligands That Can Protonate Side reaction~ involving the metal or the ligand For ligand ~ if the ligand is weak acid, then ligand can be protonated.

16. Chapter15 p Complexation with protonating ligands M + L L : the conjugate base of polyprotic acid Adding acid ~ reduces the concentration of free L available to complex with M, ~ decrease the effectiveness of L as a complexing agent. Le Châtelier’s principle

17. Chapter15 p 草酸

18. Chapter15 p Conditional Formation Constant (Effective Formation Constant) ~ ~ the effect of pH on the free ligand concentration in a complexation reaction.

19. Chapter15 p At a particular pH value,  2 is constant

20. Chapter15 p § Titrations with Inorganic Complexing Agents

21. Chapter15 p 455 Figure 17-1 Titration curves for complexometric titrations. Titration of 60.0 mL of a solution that is 0.020 M in metal M with (A) a 0.020 M solution of the tetradentate ligand D to give MD as the product; (B) a 0.040 M solution of the bidentate ligand B to give MB 2 ; and (C) a 0.080 M solution of the unidentate ligand A to give MA 4. The overall formation constant for each product is 10 20.

22. Chapter15 p 456

23. Chapter15 p 458

24. Chapter15 p § Aminocarboxylic Acid Titrations Ethylenediaminetetraacetic acid [EDTA] 458 The EDTA molecule has six potential sites for bonding a metal ion.

25. Chapter15 p Four carboxyl group ~~~ H 4 Y 代表 EDTA Acidic Properties of EDTA

26. Chapter15 p 459 Figure 17-2 Composition of EDTA solutions as a function of pH.

27. Chapter15 p 460 Figure 17F-1 Structure of H 4 Y and its dissociation products. Note that the fully protonated species H 4 Y exists as the double zwitterion with the amine nitrogens and two of the carboxylic acid groups protonated. The first two protons dissociate from the carboxyl groups, while the last two come from the amine groups.

28. Chapter15 p 461 Figure 17-3 Structure of a metal/EDTA complex. Note that EDTA behaves here as a hexadentate ligand in that six donor atoms are involved in bonding the divalent metal cation.

29. Chapter15 p § Complexes of EDTA and Metal Ions  The reagent combines with metal ions in a 1:1 ratio regardless of the charge on the cation.

30. Chapter15 p 462

31. Chapter15 p § Equilibrium Calculations Involving EDTA  A titration curve for the reaction of M n+ and EDTA ~ ~ ~ a polt of pM versus reagent volume

32. Chapter15 p From 15H Tetraacetic acid ~~~ H 4 Y H 3 Y - H 2 Y 2- HY 3- Y 4- C T = [Y 4- ] + [HY 3- ] + [H 2 Y 2- ] + [H 3 Y - ] + [H 4 Y]

33. Chapter15 p Conditional Formation Constants

34. Chapter15 p

35. 464

36. Chapter15 p Example 17-1 Calculate the molar Y 4- concentration in a 0.0200M EDTA solution buffered to a pH of 10.00 試求下列溶液的 [Y 4- ] ， 0.0200 M EDTA 溶液， pH 值為 10.0

37. Chapter15 p Calculation of the cation concentration in EDTA solutions Conditional formation constant

38. Chapter15 p Example 17-2 Calculate the equilibrium concentration of Ni 2+ in a solution with an analytical NiY 2- concentration of 0.0150M at pH (a) 3.0 and (b) 8.0 計算在不同 pH 值下， 0.0150M 的 [NiY 2- ] 溶液中有多少 [Ni 2+ ] 利用 conditional formation constant 解題

39. Chapter15 p Example 17-3 Calculate the concentration of Ni 2+ in a solution that was prepared by mixing 50.0mL of 0.0300M Ni 2+ with 50.00mL of 0.05M EDTA. The mixture was buffered to a pH of 3.0 將 50.0mL ， 0.0300M Ni 2+ 與 50.00mL ， 0.05M EDTA 溶液混 合，並將混合液的 pH 值調整至 3.0 。試計算 Ni 2+ 的濃度

40. Chapter15 p Example 17-4 Use a spreadsheet to construct the titration curve of pCa versus volume of EDTA for 50.00mL of 0.00500M Ca 2+ being titrated with 0.0100M EDTA in a solution buffered to a constant pH of 10.0 § EDTA Titration Curves 467 在 pH 值為 10.0 時，利用 0.0100M EDTA 溶液滴定 50.00mL 0.00500M Ca 2+ 溶液，並建構其滴定曲線 pCa vs EDTA( 體積 )

41. Chapter15 p 467 Figure 17-5 Spreadsheet for the titration of 50.00 mL of 0.00500 M Ca 2+ with 0.0100 M EDTA in a solution buffered at pH 10.0.

42. Chapter15 p 470 Figure 17-6 EDTA titration curves for 50.0 mL of 0.00500 M Ca 2+ (K’ CaY =1.7 5×10 10 ) and Mg 2+ (K ’ MgY =1.72×10 8 ) at pH 10.0. Note that because of the larger formation constant, the reaction of calcium ion with EDTA is more complete, and a larger change occurs in the equivalence-point region. The shaded areas show the transition range for the indicator Eriochrome Black T.

43. Chapter15 p 470 Figure 17-7 Influence of pH on the titration of 0.0100 M Ca 2+ with 0.0100 M EDTA. Note that the end point becomes less sharp as the pH decreases because the complex formation reaction is less complete under these circumstances.

44. Chapter15 p 471 Figure 17-8 Titration curves for 50.0 mL of 0.0100 M solutions of various cations at pH 6.0.

45. Chapter15 p 471 Figure 17-9 Minimum pH needed for satisfactory titration of various cations with EDTA. (From C.N.Reilley and R.W.Schmid, Anal. Chem., 1958,30,947.copyrigh 1958 American Chemical Society. Reprinted with permission of the American Chemical Society.)

46. Chapter15 p pH increase ~ ~ [OH - ] § The Effect of Other Complexing Agents on EDTA Titration Curves 會產生 M(OH) x 的化合物 An auxiliary complexing agent is needed to keep the cation in solution, cause the end points to be less sharp. Auxiliary: 輔助的

47. Chapter15 p 472 Figure 17-10 Influence of ammonia concentration on the end point for the titration of 50.0 mL of 0.00500 M Zn 2+. Solutions are buffered to pH 9.00. The shaded region shows the transition range for Eriochrome Black T. Note that ammonia decreases the change in pZn in the equivalence-point region.

48. Chapter15 p Feature 17-5 EDTA titration curves when a complexing agent is present 鋅一般為 4 配位  M 只與 NH 3 的濃度， Zn(NH 3 ) x 的形成常數有關

49. Chapter15 p α M : the fraction of the total metal or metal complex concentration existing K” ZnY : 在特定 pH 與特定 NH 3 濃度下的條件形成常數

50. Chapter15 p Example: calculate the pZn of solutions prepared by adding 20.0, 25.0, and 30.0 mL of 0.0100M EDTA to 50.0 mL of 0.00500M Zn 2+. Assume that both the Zn 2+ and EDTA solutions are 0.100M in NH 3 and 0.175M NH 4 Cl to provide a constant pH of 9.0 在 pH 值為 9.0 的緩衝溶液中 (NH 3 +NH 4 Cl) ，利用 0.0100M EDTA 溶液滴定 50.00mL 0.00500M Zn 2+ 溶液，求 pZn 值。 EDTA 體積 (a) 20.0 mL (b)25.0 mL (c) 30.0 mL K” ZnY : 在特定 pH 與特定 NH 3 濃度下的條件形成常數

51. Chapter15 p 476 Figure 17-11 Structure and molecular model of Eriochrome Black T. The compound contains a sulfonic acid group that completely dissociates in water and two phenolic groups that only partially dissociate.

52. Chapter15 p 478 Figure 17-12 Structural formula and molecular model of Calmagite. Note the similarity to Eriochrome Black T (see Figure 17-11).

53. Chapter15 p Example 17-5 Determine the transition ranges for Eriochrome Black T in titrations of Mg 2+ and Ca 2+ at pH 10.0, given that (a) the second acid dissociation constant for the indicator is (b) The formation constant for MgIn - is (c) Ca 2+ K f = 2.5x10 5 在 pH 值為 10.0 的溶液中，利用 EBT 當指示劑，滴定 Ca 2+ 與 Mg 2+ 時， EBT 的變色範圍。

54. Chapter15 p 482 Figure 17F-2 Typical kit for testing for water hardness in household water.