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Cell diagram electrode

Posted: Wed Feb 08, 2017 4:43 pm
by Cowasjee_Sanaea_3E
I understand that when half reactions don't have a solid that it needs an electrode (such as Pt).
However I was confused as to why question 14.13 needs an electrode for I:

Ce 4+ (aq) + I- (aq) --> I2(s) + Ce3+(aq)

I understand that Ce needs an electronde because both are aqueous. But I thought since "I" has a solid it doesn't need an electrode? Does it need one because it isn't a conductor?
How do we know?

Re: Cell diagram electrode

Posted: Wed Feb 08, 2017 8:07 pm
by Chem_Mod

If either the reduction or oxidation half-reaction has an aqueous species on both sides (in this case, it's the reduction half-reaction), then you need an inert conductor. If there were no Pt electrode, then there wouldn't be any way for the excess electrons from the reduction half-reaction to be transferred to the oxidation half-reaction, even if the oxidation part has a solid metal.

Hope this helps!