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

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

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

294 pH dependence of redox reaction MnO 4 - Mn e - + 4H 2 O +8H++8H+  =  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

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

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-

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+ 

If the Calomel is the positive pole e e-e- Hg Hg e -

If the Calomel is the positive pole e e-e- Hg Hg e - Hg Cl - Hg 2 Cl 2

Electrode process : Hg 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 Cl - K + + Cl - KCl (solid) 2. Saturated solution:

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  =  *log  Ag + 

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

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

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

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

cm Specific conductance decreases if the concentration decreases

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)

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.

2919   NAD + /NADH  Pyruvate/lactate NADH +H + + pyruvate NAD + + lactate Reversible redox systems Emf  Appendix 1

0000 NADH +H + + pyruvate red. ox. NAD + + lactate ox. red.   = V   = V Emf  = 0.13 V Reversible redox systems Appendix 2

2921  V   = V   = V H 2 + 1/2O 2 H2OH2O Irreversible redox systems Appendix 3

2922 Electrode process : Hg 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

2923 pH HH 