1. THE ELECTROD AND REDOX POTENTIIALS.
Department of Bioorganic and Biological Chemistry. Bioinorganic chemistry. I COURSE
LECTURE 7.
THE ELECTROD AND REDOX POTENTIIALS.
LECTURER: Professor A.D.DZHURAEV

2. The LECTURE PURPOSE:
Give an idea of ​​the students about the electrodes, redox potentials and mechanisms of their occurrence. Know that determining the redox potentials for the various biochemical systems can predict the direction of the reaction. Know that in the medical practice, a lot of methods based on the measurement of potentials, and determine the nature of disorders of the heart, brain, muscle redox potentials and in general, the laws of equilibrium processes taking place at the electrodes are of great importance in studying the life of the human.

3. The LECTURE PURPOSE:
To introduce the students with electrode and redox potentials , and mechanism of their rise. Determined redox potentials for different biochemical systems is possible to predict the direction of reactions. Many processes in organism it is impossible to explain without redox potentials. The total bioelectric potentials of different systems and organs reflect their functional state. In medical practices used many methods, founded on measurement of potentials, and defining nature of the breach of the work of heart, brain of the muscles and others. In this connection future physician must to know, how appear the potentials and how their to measure. In this connection is considered also method of potentiometric titration. Potentiometric determination of pH is the most exact, broadly applicable method for determination of active acidity of the medium, including blood and other biological liquids.

4. DEALT of questions kinds of potentials
The emergence of electrochemical potential
Measurement and calculation of the electrochemical potential
The emergence of the redox (red-ox) potential
Unlike red-ox potential of electrochemical potential
Galvanic cells and electrodes
The value of red-ox potential in medicine

5. Kinds of potentials
1. Diffuse potential - arises at the interface of the two solutions of different concentrations
2. Contact potential - there is a border between the two types of metal
3. Oxidation-reduction potential - occurs at the boundary inert metal and a solution containing the oxidized and reduced forms of the same substance
4. Electrochemical potential - there is at the metal and water or a salt solution of the metal
5. Membrane potential - occurs at the boundary of cell membranes

6. Electrochemical potential
Electrochemical potential– occurs at the interface between metal and water or a solution of the metal:
Cu Zn - + +
CuSO4
ZnSO4

7. Nernst equation to calculate the electrochemical potentialRT
E = E ln CMe+z zF
E – electrochemical potential
E0 – normal electrode potential
R – universal gas constant
T – absolute temperature
F – Faraday number, z – valence metal
CMe+z – the concentration of metal ions

8. Galvanic element
Elements consisting of two electrodes and converts chemical energy into electrical energy is called a galvanic element
Zn / ZnSO4 / KCI / CuSO4 / Cu
ZnSO4
CuSO4
Zn + CuSO4 → Cu ZnSO4
Zn0 + Cu+2 → Cu0 + Zn+2
Zn e → Zn+2
Cu e → Cu0
Zn-
Сu+
E = E0 -

9. The electrodes The electrodes of the first kind : Си / Сu2+, Ag / Ag+
and others
Electrodes of the second kind - calomel
the electrode.

10. The electrodes Relative magnitude of the potential:
Reference Electrodes - normal hydrogen electrode
calomel and silver chloride electrodes.
Electrode measurements - glass and quinhydrone
electrodes.
Quinhydrone electrode - platinum wire lowered
in a solution containing 1 mole of quinone – C6 H4O2 and 1 mol
hydroquinone С6Н4 (ОН)2.
C6 H4O2 - С6Н4(ОН)2 ↔ C6 H4O С6Н4(ОН)2
е = e0 +

11. Scheme of the structure the glass electrodeCu
Ag/AgCl
glass membrane
0,1 M HCl
glass electrode

12. Concentration element
Е = 0,058 lg С1 / С2 Е = O,O58 lg 0,1/0,01 = 0,058 lg 10= 0,058 в * 1000 = 58 мв.

13. Diffuse potential
Diffuse potential – occurs at the interface between the two solutions of the same material with different concentrations:

14. The membrane potential
The membrane potential- Occurs from the difference of concentration of ions on either side of a biological membrane.
On the border of the outer and inner side of a biological membrane potential difference of 75 mV. Changing this value changes the order of passage of ions through the cell.

15. The redox potential
The redox potential- occurs at the boundary of an inert metal and a solution containing the oxidized and reduced forms of the same substance : Pt
[Fe3+]>[Fe2+]
Fe3+
Fe2+

16. Scheme of galvanic element
Redox systems
PtFeCl3FeCl2; PtSnCl4SnCl2
Pt K3[Fe(CN)6]  K4[Fe(CN)6]
Scheme of galvanic element
Pt K3[Fe(CN)6] AgCl; Ag
K4[Fe(CN)6] KCl
(Saturation)
Ag AgCl;HCl glass definable AgCl; Ag
[H+]=const membrane-solution KCl
[H+]=x (Saturation)

17. Peters equation RT  oxidation. form 
r = r l n
nF  Restore. form 
r – the redox potential
r0 – standard redox potential
R – universal gas constant;
T - absolute temperature;
F – Faraday number, n - number of electrons
oxides. form - the concentration of the oxidized form the substance
 recovery. form  - the concentration of the reduced form the substance

18. Peters equation r = r0 - ------- l g ---------------------
0,  oxidation. form 
r = r l g
n  Restore. form 
For difficult redox systems:
0,  oxidation. form [H+]
r = r l g