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1. Class, Wednesday, Oct 13, 2004 __________________________________________

2. Homework Assignment 05 __________________________________________ ...is from Chapters 8 & 9. The problems assigned are: 8-1, 8-4, 8-9, 8-17, 8-22, 8-29 and 9-7, 9-8, 9-10, 9-16, 9-23, 9-24 Wed, Oct 20 Prepare on regularly sized paper, one side only with multiple pages stapled.

3. Temperature Effects on pH of Buffers __________________________________________ Because the Ka values are dependent on the temperature, the pH of most buffers are dependent on the temperature. The TRIS buffer of the proceeding has an especially large T dependence of -0.031 pKa units / oC.

4. The TRIS Buffer Solutions __________________________________________ TRIS buffer – mixture of {Tris(hydroxymethyl)aminomethane and Tris(hydroxymethyl)aminomethane hydrochloride} pKa = 8.08

5. Effects of Ionic Strength on Buffers __________________________________________ The total ionic environment in the solution (ionic strength,  or I) may also affect the pH of a buffer. Contrary to what is generally thought, a 10-fold dilution of a 0.5M solution of a dihydrogen / monohydrogen phosphate changes the pH from 6.6 to 6.9 because the decreased ionic strength. Some control of this effect is possible by making the total ionic strengths equal by adding electrolytes like NaCl or KNO3 that have no acid or base properties.

6. Additional Buffers __________________________________________ The textbook shows additional systems that are commonly used to prepare various pH buffer solutions in Table 9–2, page 184.

7. Acid-Base Indicators __________________________________________ Visual indicators that may be used in the determination of an end point in acid or base titrations are themselves weak acids or bases whose protonated or deprotonated forms exhibit two distinct colors.

8. Acid-Base Indicators – Bromocresol green __________________________________________

9. Acid-Base Indicators – Thymol Blue __________________________________________

10. Acid-Base Indicators __________________________________________

11. Acid-Base Indicators __________________________________________ We will talk in greater detail later regarding the choice of an indicator for an acid/base titration. At this time it is sufficient to say that the indicator should have a color transition that occurs closely to the pH of the solution mixture at the equivalence point for that titration.

12. Carbonless Copy Paper __________________________________________

13. Carbonless Copy Paper __________________________________________

14. Start Chapter 13 – EDTA __________________________________________ • EDTA is an abbreviation for ethylenediamine tetraacetic acid. EDTA form strong 1 : 1 complexes with many metal ions; the coordination is through the 4 O atoms and 2 N atoms

15. Chelates or ligands __________________________________________ EDTA is the most widely used reagent of a class of materials known as chelates, or polydentate ligands. Ligands are compounds that may act as good Lewis Bases, i.e., electron pair donors. If the ligand has several pairs of electrons, it may function as a polydentate ligand.

16. Ligands __________________________________________ In the simple ligand reaction, the ligand acts as a Lewis base and the metal ion as a Lewis acid. [Ag+] + 2 :N= C -< == >[Ag(CN)2 ] - Lewis Acid Lewis Base Complex

17. EDTA __________________________________________ EDTA is a hexa-pronated ligand; the 6 of the pKa values of EDTA are given above.

18. EDTA __________________________________________ Predominant form of EDTA as a function of pH

19. EDTA __________________________________________ The fraction () of a possible form of a multi-pronated ligand is a function of the pH or [H+] of the solution. Y-4 = [Y -4] / [EDTA] Total We will not derive it at this time, but Y-4 = (K1…Kn) / [H+]n + [H+]n-1K1 + [H+]n-2K1 K2 + …  (K1…Kn) It is a plot of  values, (0 to n) that is plotted in the next slide.

20. Fractional Composition of Poly-protonic Ligands as f(pH) __________________________________________ Predominant form of EDTA as a function of pH

21. Fractional Composition of Poly-protonic Ligands as f(pH) __________________________________________ Graph of Predominant form of EDTA as a function of pH

22. Formation Constants __________________________________________ For complexes of the formulas [MXn]q, (where n > 1) the reactions occurs by stepwise fashion as shown in the following series. M + X < == > MX K1 = [MX] / [M][X] MX + X < == > MX2 K2 = [MX2] / [MX][X] ….. ….. MXn-1 + X < == > MXn Kn = [MXn] / [MXn-1][X] The net reaction for the formation of MXn is the sum of these step reactions; The overall formation constant is defined as I and is equal to the product of the individual K values, ie, I = K1K2 …Kn