The new finding here, that the conventional standard potentials (based on S.H.E.) are linearly dependent on ionization potentials, has yielded the absolute values of aqueous standard potentials

Raji Heyrovska

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Absolute Aqueous Redox Potentials ( via a new link between aqueous and gaseous properties)

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1ABSOLUTE AQUEOUS REDOX POTENTIALS
(via a new link between aqueous and gaseous properties)
Raji Heyrovská
Institute of Biophysics, Academy of Sciences of the Czech Republic,
135 Kralovopolská, 612 65 Brno, Czech Rep. Email: rheyrovs@hotmail.com
Presented at: 
9. Pracovní setkání fyzikálních chemik  a elektrochemik , Brno,ů ů  29. a 30.
ervna 200č 9 (http://www.chemi.muni.cz/~libuse/setkani2009/index.html)
(9th Workshop of Physical Chemists and Electrochemists, Brno, 29th and 30th June 2009)
on the occasion of the 3 main anniversaries, 
1) 90th: foundation of Masaryk Univ. (MUNI), 
2) 90th: foundation of Mendel Univ. of Agriculture & Forestry (MUAF), 
3) 50th: award of the Nobel Prize in 1959 to Professor J. Heyrovský, 
and also 3 more anniversaries,
4) 70th: survival of MUNI & MUAF in 1939, 
5) 40th: survival of MUNI & MUAF again in 1969 and 
6) 20th: “ velvet revolution”  in 1989. 
*********
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21. INTRODUCTION
“ Chemistry is electric”  (Bk: M.E. Bowden, CHF, 1997)
Tomato and Lemon batteries:
http://www.funsci.com/fun3_en/electro/electro.htm   http://www.youtube.com/watch?v=AY9qcDCFeVI
Electrolyte: acidic juice, Electrodes: copper (+) and zinc (-).
Chemical reactions at the two half cells: (1) Cu++ + 2e- ==> Cu and (2) Zn
==> Zn++ + 2 e- ; the overall reaction is Zn + Cu++ ==> Zn++ + Cu.
The cell voltage is the “ potential difference“  between the two half cells.
Electrochemists have chosen by convention, the potential of the standard
hydrogen electrode (S.H.E.) as zero. The redox reaction for this half cell is
2H+ + 2e- <==> H2. The standard potentials, Eo(S.H.E.) of Cu and Zn are
+0.34 and -0.76 V and the cell voltage is, E = +0.34 - (-0.76) = +1.10 V.
(Note: The unit of potential is named volt, in honor of Volta)
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31. INTRODUCTION (contd.)
Latest news on S.H.E. : “ ..universal reference electrode for
which, under standard conditions, the standard electrode potential
(H+/H2) is zero at all temperatures: Last update: 2009-06-16;
http://goldbook.iupac.org/S05917.html
There have been attempts in the past to obtain the absolute value of
the potential of the S.H.E. (Bard et al [1]). Trasatti (1986) [2]
suggested, by theoretical calculations, the value 4.44 (+/-) 0.04V.  
Recently, Donald et al (2008) [3] obtained for S.H.E. (by electron
capture on gaseous phase nano-drops) the value, 4.20 (+/-) 0.4 V. 
The “ new observation here”  that Eo varies linearly with the
ionization potentials (I) for many groups of elements, has given 
the “ absolute potential of the S.H.E., (EOI = 0)”  (which confirms the
value in [3]) (and can be taken as the final answer).
Thereby, the “ absolute redox potentials, have been obtained as the
sum, EOabs = EO + EOI = 0”  , (Heyrovska, [4]). 
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42. LINEAR DEPENDENCE OF AQ. STD. POTENTIALS (EO) 
ON IONIZATION POTENTIALS (I)   
The data in [1] have been used to plot Eovs I in Fig. 1, where I =
I (sum) is the sum of the 1st, 2nd, .. ionization potentials, as the
case may be, depending on the value of n, (ox + ne- = red). 
Eo = kaqI - EoI=0; absolute aq. redox potential = Eoabs = Eo + EoI=0 
EoI=0 = Abs. potl. of S.H.E. = 2.87 V (H-/H: halogens) & 4.20 V (H+/H: all others)
(Author: Raji Heyrovska, Brno Conference, 29-30 June 2009)
-5
-4
-3
-2
-1
0
1
2
3
4
0 20 40 60 80 100
Ionization potentials, I    /V
Fig. 2. Linear dependence of aq. std. potls. on I. 
A
q.
 
s
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da
rd
.
 
po
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n
tia
ls
 
(v
s
 
S
.
H
.
E
.
), 
Eo
 
 
 
 
/V
Aq. Gp.(i), Cu, Ag, Au, Tl, n = 1
Gp.(ii), F, Cl, Br, I, n = 1
Gp.(iii), H, Li$, Na, K, Rb, Cs, n = 1
Gp.(iv), Ge, Sn, Pb, Se, Pd, n = 2
Gp.(v), Fe, Co, Ni, Cd, n = 2
Gp.(ix), N, P, Cr, Ga, n = 3
Gp.(vii), O, S, Te, n = 2
Gp.(viii), Be, Mg, Ca, Sr, Ba, Ra, n = 2
Gp.(xi), B, Al, Sc, Y, La, n = 3
Gp.(xii), Ti, Zr, n = 4
Gp.(vi), Mn, Zn, n = 2
Gp.(x),Al$, Eu, n = 3
(Tl, n = 1), Cu, Pb, Cd, Zn, Mn, Ba (n = 2),
Al (n = 3): $E1/2 (J. H. & D.I., 1935)
- - - , Cu, Ba, n = 2, E1/2
(i)
(ii)
(iii)
(iv)
(v)
(vii)
(viii)
(x)
(xi)
Lineární (Gp.(v), Fe, Co, Ni, Cd, n = 2)
Lineární (Gp.(ix), N, P, Cr, Ga, n = 3)
Lineární (Gp.(vi), Mn, Zn, n = 2)
Lineární (Gp.(x),Al$, Eu, n = 3)
Lineární (Gp.(viii), Be, Mg, Ca, Sr, Ba, Ra,
n = 2)
Lineární (- - - , Cu, Ba, n = 2, E1/2)
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5All the straight lines in Fig. 1 follow the simple equation, 
Eo = kaqI – EoI=0 ; Eoabs = Eo + EoI=0 (= kaqI)                            (1a,b)
                                             
where kaq is the slope, “ EoI=0 is the absolute potential of the S.H.E.” and
“ Eoabs is the absolute redox potential” . Eoabs = EoI=0 when Eo = 0 (Eq. 1b).
     For Gp. VIIA (halogens, (1/2)X2/X-), EoI=0 = 2.87 (+/-) 0.01 V, and for 
the others, EoI=0 = 4.20 (+/-) 0.03 V, which correspond to the (1/2)H2/H-
and H+/H redox
 
equilibria resply. Fig. 2 shows plots of Eoabs (= kaqI) vs Eo.
     The slopes (kaq) of the lines have been used as criteria for classifying
the redox couples into groups (i) to (xii) (see: the box in Fig. 1). 
y = 1.003x + 4.204
R2 = 0.999
y = 0.999x + 2.871
R2 = 0.999
0
1
2
3
4
5
6
7
-5 -4 -3 -2 -1 0 1 2 3
Aqueous standard potentials, Eo (vs. S.H.E.)   /V
Fig. 2: Absolute aq. std. potentials, Eoabs (calculated as kaqI) vs Eo.              
A
b
s
o
lu
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a
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.
 
s
td
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p
o
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a
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Eo
a
b
s
 =
 
k a
qI 
 
 
/V
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63. DEPENDENCE OF POLAROGRAPHIC HALF-WAVE POTENTIALS (E1/2) 
ON  IONIZATION POTENTIALS (I)    
Fig. 3 shows the E1/2 values for Cu, Pb, Cd, Zn, Mn, Ba (n = 2 for all)
Al (n = 3) (Heyrovsky, Ilkovic [5a,b]) and Tl (n = 1) (Heyrovsky,
Kuta [6]). The causes for the differences between Eo and E1/2 in
some cases (here, Ba and Al) have been explained by Lingane [7].
-5
-4
-3
-2
-1
0
1
2
3
4
0 20 40 60 80 100
Ionization potentials, I    /V
Fig. 3. Linear dependence of Eo on I. 
Red filled circles: E1/2 values 
A
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.
 
s
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.
 
p
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(v
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S
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H
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), 
Eo
 
 
  
/V
Aq. Gp.(i), Cu, Ag, Au, Tl, n = 1
Gp.(ii), F, Cl, Br, I, n = 1
Gp.(iii), H, Li$, Na, K, Rb, Cs, n = 1
Gp.(iv), Ge, Sn, Pb, Se, Pd, n = 2
Gp.(v), Fe, Co, Ni, Cd, n = 2
Gp.(ix), N, P, Cr, Ga, n = 3
Gp.(vii), O, S, Te, n = 2
Gp.(viii), Be, Mg, Ca, Sr, Ba, Ra, n = 2
Gp.(xi), B, Al, Sc, Y, La, n = 3
Gp.(xii), Ti, Zr, n = 4
Gp.(vi), Mn, Zn, n = 2
Gp.(x),Al$, Eu, n = 3
(Tl, n = 1), Cu, Pb, Cd, Zn, Mn, Ba (n = 2),
Al (n = 3): $E1/2 (J. H. & D.I., 1935)
- - - , Cu, Ba, n = 2, E1/2
(i)
(ii)
(iii)
(iv)
(v)
(vii)
(viii)
(x)
(xi)
Lineární (Gp.(v), Fe, Co, Ni, Cd, n = 2)
Lineární (Gp.(ix), N, P, Cr, Ga, n = 3)
Lineární (Gp.(vi), Mn, Zn, n = 2)
Lineární (Gp.(x),Al$, Eu, n = 3)
Lineární (Gp.(viii), Be, Mg, Ca, Sr, Ba, Ra,
n = 2)
Lineární (- - - , Cu, Ba, n = 2, E1/2)
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7ACKNOWLEDGEMENTS
The author thanks the Institute of Biophysics for institutional grant Nos. 
AV0Z50040507 and AV0Z50040702 of the ASCR and the Organizers of this 
conference for the opportunity given to present the “ new”  scientific results.
LITERATURE
•  Bard, A.J., et al.: Standard potentials in aqueous solutions, Marcel Dekker, 1985, 
NY.
•  Trasatti, S.: Pure & Appl. Chem. 58 (1986) 955.
•  Donald, W.A., et al.: J. Am. Chem. Soc. 130 (2008) 3371.
•  Heyrovska, R.: submitted
•  a) http://nobelprize.org/nobel_prizes/chemistry/laureates/1959/; 
b) Heyrovsky, J., Ilkovic, D.: Chem. Listy, XXIX (1935) 234; Collection VII (1935) 198.
6. Heyrovsky, J., Kuta, J.: Principles of Polarography, Publishing House of the CAS, 
1965, Prague.
7. Lingane, J.J.: J. Am. Chem. Soc.  61 (1939) 2099.
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Absolute Aqueous Redox Potentials ( via a new link between aqueous and gaseous properties)

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