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Postby 705121606 » Sat Feb 29, 2020 6:56 pm

In this question, it told us that a 1.0M NiSO4 (aq) solution was electrolyzed by using inert electrodes then asks for the cathode and anode reaction. I wrote the reaction for Ni2+ + 2e- --> Ni from the NiSO4 given in the equation but didn't know if that was the cathode or anode.

Since this is saying it is in an aqueous solution, do we assume the other reaction has to be water?

The solutions manual says for the cathode we want the reduction potential that is most positive and for the anode we want the reduction potential that is most negative.

Can someone walk through the thought process of this question for me

Tyler Angtuaco 1G
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Joined: Wed Sep 11, 2019 12:16 am

Re: 6O.1

Postby Tyler Angtuaco 1G » Sat Feb 29, 2020 7:43 pm

I assumed that Ni2+ ions would be reduced since it was present as an aqueous solution and not solid. I also considered the possibility of the SO4 2- ion to reduce, but I realized that the reduction reaction present in Appendix 2B mentions H2SO3 as a product, which is not mentioned in the question so I didn't use it as my reduction reaction. Then, I knew that water would be the oxidized since the question mentioned inert electrodes, which don't contribute towards a reaction. I used the oxidation reaction with standard potential 1.23V rather than the one with 1.78V since it was more negative or less positive.

But, I also am not entirely sure about this question either. Here was what I was wondering:
-Do we just assume Ni(s) forms as a precipitate? Or does it actually thicken the electrode, which I am skeptical about since the electrode is supposedly inert?
-Do we just disregard SO4 2- because the solution does not mention the expected production of H2SO3 if it is reduced?
-If it is wrong to disregard the possibility of Ni(s) to be present in the solution at the start, why can Ni(s)->Ni2+ not be the oxidation reaction and water as the reduction reaction if we are choosing the most positive standard potential for the cathode and the most negative for the anode? The standard cell potential for Ni2+ is -0.23 and the standard cell potential for water is +1.23V.

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