Do these half-reactions have electrode potential that depends on pH?

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The electrode potentials of the half-reactions for Br2, Cl2, I2, and S2O8 do not depend on pH, as indicated by the Pourbaix diagrams. While H+ or OH- ions are not included in the Nernst equation for these reactions, the chemical balance can be influenced by pH under certain conditions. Specifically, for halides, aqueous Cl2 is unstable above pH 2, reacting with water to form hypochlorite, which does have a pH-dependent redox potential. This indicates that while some reactions may not show direct pH dependence, the stability of the species involved can be affected by pH, potentially altering the reaction dynamics.
Dolphinsea14
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Do following half-reactions have electrode potential that depends on pH? I know H+ or OH- ions wouldn't be included in Nernst equation for these, but would pH affect chemical balance in these reactions, and therefore electrode potentials?
Br2+2e- -> 2Br-
Cl2+2e- -> 2Cl-
I2+2e- -> 2I-
S2O8+2e- -> 2SO42-?
 
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Yes. You can google the Pourbaix diagrams for these species to find the dependence.
Dolphinsea14 said:
I know H+ or OH- ions wouldn't be included in Nernst equation for these, but would pH affect chemical balance in these reactions, and therefore electrode potentials?
This isn't quite true. At least for the halides, in water one of the stable species that is formed in highly oxidizing conditions is hypohalite, which entails reaction between the halide and water.
 
Cl2-Cl- electrode potential.png

I found this in a book (Inorganic Chemistry by Shriver and Atkins). It seems redox potential in these cases doesn't depend on pH.
 
Ok, yes for the Cl2/Cl- couple specifically, there is no dependence on pH. You can see this on the Pourbaix diagram for chlorine as a horizontal line at low pH and high voltage (it's easier to see in the bromine diagram):
1567778959911.png

But it's kind of a weird statement to make, because aqueous Cl2 is not stable above pH 2 or so. It reacts with water to form HOCl, which gets deprotonated at high pH to give hypochlorite. Note that the redox potential for Cl-/hypochlorite is dependent on pH.
 
In other words: there is no dependence on pH, just the reaction doesn't occur when the pH is high enough (so whole discussion becomes a moot).
 
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