1. What happens to the absorbed energy?

2. Energy soso s1s1 t1t1

5. EDTA Titrations

6. Outline What is EDTA? What is EDTA? Metal-Chelate Complexes Metal-Chelate Complexes ATP 4- with Mg 2+ Fe(NTA) 2 3- Fe(DTPA) 2- Chelate Effect Chelate Effect EDTA EDTA Acid Base Properties  Y nomenclature Conditional Formation Constants EDTA Titration EDTA Titration

7. Metal-Chelate Complexes Lewis Acid/Base Chemistry Monodentate Multidentate and Chelates

8. Review: What is a Lewis Acid? Examples? And a Lewis Base? Examples?

9. Transition Metal with ligand Central Metal ion is a Lewis Acid Ligand – All ligands are Lewis Bases

10. Multidentate Multidentate or chelating ligand attaches to a metal ion through more than one atom is said to be multidentate, or a chelating ligand. Examples?

12. ATP 4- can also form complexes with metals

13. Complex of Iron and NTA Fe 3+ + Fe(NTA) 2 3- 2

14. Medical Applications The Thalassemia Story

18. The Chelate Effect Question: Describe in your own words, the “chelate effect”.

19. The Chelate Effect! Cd(H 2 O) 6 2+ + 2 Cd(H 2 O) 6 2+ + 4CH 3 NH 2 + 4 H 2 O K = B 2 = 8 x 10 9 + 4 H 2 O K = B 2 = 4 x 10 6

20. 13-2 EDTA “EDTA is by far, the most widely used chelator in analytical chemistry. By direct titration or through indirect series of reactions, virtually every element of the periodic table can be measured with EDTA.” - Daniel Harris

21. Acid/Base Properties H H (H 6 Y 2+ )

22. Acid/Base Properties H (H 5 Y + ) pK a = 0.0

23. Acid/Base Properties (H 4 Y) pK a = 0.0 pK a = 1.5

24. Acid/Base Properties (H 3 Y - ) pK a = 0.0 pK a = 1.5 - pK a = 2.0

25. Acid/Base Properties (H 2 Y -2 ) pK a = 0.0 pK a = 1.5 - pK a = 2.0 - pK a = 2.7

26. Acid/Base Properties (HY -3 ) pK a = 0.0 pK a = 1.5 - pK a = 2.0 - pK a = 2.7 pK a = 6.16

27. Acid/Base Properties (Y -4 ) pK a = 0.0 pK a = 1.5 - pK a = 2.0 - pK a = 2.7 pK a = 6.16pK a = 10.24

28. Fraction as Y 4- The fraction of EDTA in form Y 4- is given as  4- (13-3) Concentration in the form Y 4- Total Concentration of EDTA Fraction of EDTA ion the form Y 4-

29. Fraction as Y 4- Equation 13-4 in text

31. Example You make a solution of 0.10 M EDTA and you buffer the pH to (a) 10.0. What is  Y4- ? (b) What is  Y4- if the pH of the solution is buffered to 11.0?

33. EDTA reactions with Metals Silver – Ag + Mercury - Hg 2+ Iron (III) – Fe 3+

34. EDTA ethylenediaminetetraacetate anion => EDTA -4 => Y -4 +1 cation Ag + + Y -4  AgY -3

35. EDTA ethylenediaminetetraacetate anion => EDTA -4 => Y -4 +2 cation Hg +2 + Y -4  HgY -2

36. EDTA ethylenediaminetetraacetate anion => EDTA -4 => Y -4 +3 cation Fe +3 + Y -4  FeY -1

37. EDTA ethylenediaminetetraacetate anion => EDTA -4 => Y -4 +n ion M +n + Y -4  MY (n-4)+

38. EDTA [MY (n-4)+ ] K MY = -------------- [M][Y -4 ] [MY (n-4)+ ] K MY = ------------------- [M +n ] *  4 * [EDTA] [MY (n-4)+ ] K' MY = K MY x  4 = ------------------- [M +n ] [EDTA] Conditional formation constant!

40. Example Calculate the concentration of Ni 2+ in a solution that was prepared by mixing 50.0 mL of 0.0300 M Ni 2+ with 50.0 mL of 0.0500 M EDTA. The solution was buffered to pH of 3.00. Two Parts 1. Reaction 2. Then equilibrium is established

41. EDTA Titrations

43. Figure 13- 10 Theoretical titration curves

44. EXAMPLE: Calculate the conditional constant: Derive a curve (pCa as a function of volume of EDTA) for the titration of 50.0 mL of 0.0500 M Ca +2 with 0.1000 M EDTA in a solution buffered to a constant pH of 10.0. pCa at Equivalence Equivalence Volume pCa at Pre-Equivalence Point pCa at Post-Equivalence Point pCa at Initial Point

45. Example Derive a curve (pCa as a function of volume of EDTA) for the titration of 50.0 mL of 0.0500 M Ca +2 with 0.1000 M EDTA in a solution buffered to a constant pH of 10.0. [CaY -2 ] K' CaY = K CaY *  4 = ---------------- [Ca +2 ] * [EDTA] where  Y4- = 0.36at pH = 10.0 K' CaY = K CaY *  4 = 4.9 x 10 10 * 0.36 = 1.8 x 10 10 K CaY = 4.9 x 10 10

46. EXAMPLE: Derive a curve (pCa as a function of volume of EDTA) for the titration of 50.0 mL of 0.0500 M Ca +2 with 0.1000 M EDTA in a solution buffered to a constant pH of 10.0. Equivalence Volume 1 Mole of EDTA = 1 Mole of Metal M 1 V 1 = M 2 V 2 (Careful of Stoichiometry) 50.0 mL (0.0500 M) = 0.1000 M (V 2 ) V 2 = 25.0 mL

47. EXAMPLE: K' CaY = 1.8 x 10 10 0.00 mL EDTA added pCa = - log[Ca +2 ] Initial Point = - log(0.00500 M) = 2.301 Derive a curve (pCa as a function of volume of EDTA) for the titration of 50.0 mL of 0.0500 M Ca +2 with 0.1000 M EDTA in a solution buffered to a constant pH of 10.0.

48. EXAMPLE: Derive a curve (pCa as a function of volume of EDTA) for the titration of 50.0 mL of 0.0500 M Ca +2 with 0.1000 M EDTA in a solution buffered to a constant pH of 10.0. At 25.0 mL (Equivalence Point) Ca 2+ + Y 4- ->CaY 2- Before 0.0025 moles - After - - 0.0025 moles What can contribute to Ca 2+ “after” reaction?

49. EXAMPLE: Derive a curve (pCa as a function of volume of EDTA) for the titration of 50.0 mL of 0.0500 M Ca +2 with 0.1000 M EDTA in a solution buffered to a constant pH of 10.0. Ca 2+ + Y 4-  CaY 2- I - - 0.0025 moles/V C +x +x -x E +x + x 0.0333 –x X = [Ca 2+ ] = 1.4 x10 -6 pX = p[Ca 2+ ] = 5.86 6 0.0025moles/0.075 L

50. Pre-Equivalence Point Let’s try 15 mL

51. EXAMPLE: Derive a curve (pCa as a function of volume of EDTA) for the titration of 50.0 mL of 0.0500 M Ca +2 with 0.1000 M EDTA in a solution buffered to a constant pH of 10.0. At 15.0 mL Ca 2+ + Y 4- ->CaY 2- Before 0.0025 moles 0.0015 moles - After 0.0010 moles - 0.0015 moles What can contribute to Ca 2+ after reaction? K’ CaY = 1.8 x 10 10 negligible

52. EXAMPLE: Derive a curve (pCa as a function of volume of EDTA) for the titration of 50.0 mL of 0.0500 M Ca +2 with 0.1000 M EDTA in a solution buffered to a constant pH of 10.0. At 15.0 mL [Ca 2+ ] = 0.0010 moles/0.065 L [Ca2+] = 0.01538 4 M p [Ca2+] = 1.81 2

53. Post Equivalence Point Let’s Try 28 ml

54. EXAMPLE: Derive a curve (pCa as a function of volume of EDTA) for the titration of 50.0 mL of 0.0500 M Ca +2 with 0.1000 M EDTA in a solution buffered to a constant pH of 10.0. At 28.0 mL Ca 2+ + Y 4- ->CaY 2- Before 0.0025 moles 0.0028 moles - After - 0.0003 moles0.0025 moles What can contribute to Ca 2+ after titration?

55. EXAMPLE: Derive a curve (pCa as a function of volume of EDTA) for the titration of 50.0 mL of 0.0500 M Ca +2 with 0.1000 M EDTA in a solution buffered to a constant pH of 10.0. Ca 2+ + Y 4-  CaY 2- I - 0.0003 moles/V 0.0025 moles/V C +x +x -x E +x 0.003846 + x 0.03205 –x X = [Ca 2+ ] = 4.6 x10 -10 pX = p[Ca 2+ ] = 9.33 4 0.078 L

57. Experimental Considerations

58. EDTA Titration Techniques Erichrome Black T MgIn + EDTA  MgEDTA + In (red) (colorless) (blue)

59. Figure 13-13 Guide to EDTA titrations, light color, pH range for quantitative analysis, dark area where ammonia must be present