1. 291 Electrochemistry: Redox Reactions Electrochemistry: Redox Reactions Dr. M. Sasvári: Medical Chemistry Lectures

2. 292 Direction of the redox reaction Oxidizing or reducing agent? Oxidizing or reducing agent?

3. 293 Comparison of standard redox potentials Comparison of standard redox potentials 0 - + +1.5 Na + /Na MnO 4 - /Mn 2+ Reducing agent Oxidizing agent weakstrong weak O 2 /H 2 O H + (pH7)/H 2 I - /I 2

4. 294 pH dependence of redox reaction MnO 4 - Mn 2+ + 5 e - + 4H 2 O +8H++8H+  =  0 + 0.059 5 lg [MnO 4 - ] [H + ] 8 [Mn 2+ ] [MnO 4 - ]=0.1 M [Mn 2+ ]=0.01 M pH=1: e=1.43 V pH=7: e=0.85 V

5. 295 MUSCLE LACTATE glycogen pyruvate blood LIVER lactate pyruvate NADH NAD + NADH Biologically important reversible redox systems

6. 296 Biologically important IRREVERSIBLE redox systems Mitochondrial respiratory chain (electron transport chain) NADH + H + + 1/2O 2  H 2 O NAD + /NADH  0 = - 0,32 V 1/2O 2 /H 2 O  0 = + 1,23 V e-e-

7. 297 Constant ion concentration (saturated solution) constant  Non-polarizable Electrodes The Calomel electrode Non-polarizable Electrodes The Calomel electrode Components: Saturated solutions: Calomel ( Hg 2 Cl 2 ), KCl Metal Mercury Components: Saturated solutions: Calomel ( Hg 2 Cl 2 ), KCl Metal Mercury  =  0 + (0.06/2  *lg  Hg 2 2+ 

8. 298 - + If the Calomel is the positive pole + + + + e e-e- Hg Hg 2 2+ + 2 e -

9. 299 - + If the Calomel is the positive pole + + + + + + e e-e- Hg Hg 2 2+ + 2 e - Hg 2 2+ + 2Cl - Hg 2 Cl 2

10. 2910 1. Electrode process : Hg 2 2+ + 2 e - 2 Hg Hg 2 2+ Hg Hg 2 Cl 2 2Cl - KCl Solid phase Liquid phase If the Calomel is the positive pole: Hg 2 Cl 2(solid) Hg 2 2+ + 2Cl - K + + Cl - KCl (solid) 2. Saturated solution:

11. 2911 Constant ion concentration (saturated solution) constant  Constant ion concentration (saturated solution) constant  Non-polarizable electrodes: The Argentum electrode Non-polarizable electrodes: The Argentum electrode Components: Saturated solutions: Argentum chloride ( AgCl ), KCl A silver wire Components: Saturated solutions: Argentum chloride ( AgCl ), KCl A silver wire  =  0 + 0.06*log  Ag + 

12. 2912 - - If the Argentum electrode is the negative pole + + e e-e- Ag Ag + + e - Ag + + Cl - AgCl +

13. 2913 Electrode process : Ag + + e - Ag Ag + Ag AgCl Cl - KCl Solid phase Liquid phase If the Silver electrode is the negative pole:

14. 2914 Measuring pH with glass electrode Ion selective electrodes: a thin glass membrane inner space: HCl outer space: unknown    Argentum reference electrode

15. 2915 Specific conductance (  ): Measured data Conductivity of 1cm 3 solution CONDUCTANCE + + - - - + + - + - - - - - - - - + + + ++ + + + Measurable with conductometer (see: Practice: Conductometry)

16. 2916 1 cm 3 + + - - - + + - + - Specific conductance decreases if the concentration decreases

17. 2917 Equivalent conductance ( ): A calculated value + - - + + - + - =  * V Includes always 1 mol (1 geqv) material  = max Ka=Ka= *c*c (1 -  ) Calculation of K a from : (see before)

18. 2918 SUMMARY ELECTROCHEMISTRY (Part 3) (Ebbing: Chapter 21: Electrochemistry) Important terms: glass electrode, non- polarizable electrodes, calomel electrode, silver electrode. Important terms: Specific and equivalent conductance.

19. 2919  0 -0.32  -0.41 -0.38 -0.35 -0.32 -0.29 -0.26 1000 100 10 1 1 1 1 1 1 1 100 NAD + /NADH  -0.13 -0.16 -0.19 -0.22 -0.25 -0.28 Pyruvate/lactate 1 100 10 1 1 1 100 1 1 1 10 1000 NADH +H + + pyruvate NAD + + lactate Reversible redox systems Emf 0.28 0.22 0.16 0.10 0.04 -0.02 -0.19  Appendix 1

20. 2920 -0.5 -0.4 -0.3 -0.2 -0.1 0000 NADH +H + + pyruvate red. ox. NAD + + lactate ox. red.   = -0.32 V   = -0.19 V Emf  = 0.13 V Reversible redox systems Appendix 2

21. 2921  V  -0.5 0 0.5 1 1.5  = - 0.42 V   = +1.24 V H 2 + 1/2O 2 H2OH2O Irreversible redox systems Appendix 3

22. 2922 Electrode process : Hg 2 2+ + 2 e - 2 Hg Hg 2 2+ Hg Hg 2 Cl 2 2Cl - KCl Solid phase Liquid phase If the Calomel is the negative pole: 5/25 Appendix 4

23. 2923 pH HH 