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I was thinking about how Daniell cell works and got into a serious doubt.

Let's consider a half cell of Zn. In standard conditions, it'll have an electrode potential of -0.76V with respect to SHE. If I now increase the zinc ion concentration, I know from Nernst equation that it's electrode potential (still with respect to SHE) should become less negative. Intuitively also, it's tendency to get reduced will be more due to Le Chatelier's principle, so more reduction potential as predicted by Nernst equation. So far so good.

But, if I see it like this, then the results seem to get flawed: When I increase zinc ion concentration, in the new equilibrium state that will be attained, the absolute potential of the electrolyte will be greater (due to more positive (zinc) ions), and a little bit (safe to neglect it's consequences) of negative charge on Zn electrode will be decreased, with a little deposition of Zn. Zn2+ + 2e- <---> Zn So the net effect would be of electrolyte solution becoming more positive. Now, the definition of "reduction" potential is the (absolute) potential difference between the reduced and the oxidised species (along with some additive constant that makes SHE's electrode potential 0V, but it's of no concern here as we're seeing where the electrode potential (of Zn) increases or decreases, NOT its absolute value); hence, E = V(Zn electrode) - V(Zn2+ in electrolyte). So this should get more negative as the potential of electrolyte increases. (Potential of the electrode also becomes more negative, but its effect is marginal.)

So what is the flaw in this perspective?

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  • $\begingroup$ I'm sorry that this question was closed. I would try to help answer it if they would allow people to answer it! I saw your question also about iodine bands. Would you consider helping us to launch a brand new stack exchange just for spectroscopy and materials modeling? area51.stackexchange.com/proposals/122958/… We would very much appreciate your help, and questions like this probably won't get closed. $\endgroup$ – user1271772 Feb 8 at 22:03
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    $\begingroup$ I'd be happy to! Thanks for informing! $\endgroup$ – Atom Feb 9 at 4:01
  • $\begingroup$ ! Thank you! It appears your Area51 profile isn't linked with your Stack Exchange profile, so maybe you should follow these steps here: area51.meta.stackexchange.com/questions/29706/… $\endgroup$ – user1271772 Feb 9 at 5:54
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    $\begingroup$ Someone else had that problem too, and this is how they got it to work: area51.meta.stackexchange.com/a/29985/190792. It also helps to use Chrome's in-cognito mode, if you have that available. Does this answer help? $\endgroup$ – user1271772 Feb 9 at 19:00
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    $\begingroup$ That helped! Thanks! $\endgroup$ – Atom Feb 9 at 19:14

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