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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: dolphinsea14 on September 01, 2019, 08:16:54 PM

Title: Do following half-reactions have ph-dependent electrode potential?
Post by: dolphinsea14 on September 01, 2019, 08:16:54 PM
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- :rarrow: 2Br-
Cl2+2e- :rarrow: 2Cl-
I2+2e- :rarrow: 2I-
S2O8+2e- :rarrow: 2SO42-
Title: Re: Do following half-reactions have ph-dependent electrode potential?
Post by: Borek on September 02, 2019, 03:28:18 AM
Can you think of any side reactions involving mentioned substances and pH dependent?
Title: Re: Do following half-reactions have ph-dependent electrode potential?
Post by: dolphinsea14 on September 03, 2019, 07:31:45 PM
I'm not sure, that's why I ask. Can side reactions affect electrode potential? Wouldn't they just shift equilibrium, and wouldn't equilibrium constant in Nernst equation remain the same value as before?
Title: Re: Do following half-reactions have ph-dependent electrode potential?
Post by: Borek on September 04, 2019, 02:56:27 AM
Quote from: dolphinsea14 on September 03, 2019, 07:31:45 PM
I'm not sure, that's why I ask. Can side reactions affect electrode potential? Wouldn't they just shift equilibrium, and wouldn't equilibrium constant in Nernst equation remain the same value as before?

Constant remains the same, but what if shifting the equilibrium by a side reaction changes concentrations of an ion involved in the redox process?
Title: Re: Do following half-reactions have ph-dependent electrode potential?
Post by: dolphinsea14 on September 04, 2019, 08:06:12 AM
I found this in a book (Inorganic Chemistry by Shriver and Atkins). It seems redox potential in these cases doesn't depend on pH.
Title: Re: Do following half-reactions have ph-dependent electrode potential?
Post by: Vidya on September 06, 2019, 01:49:27 AM
You need to check the ions involved ..if they are conjugate bases of  strong acid then they will not get hydrolyzed in water like Cl- Br- and I- are weak conjugate  bases of strong acids HCl,HBr and HI.
However conjugate bases of weak acids are hydrolyzed in water and releases OH- which makes it pH sensitive.