REDPX: How can this reaction take place to begin with?

[zut212]

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How can this reaction occur if you don't have the starting material to begin with:

Be2+ 2e- -----> Be E= +1.70
Au3+ 3e- -----> Au E= +1.29


Both, the Be2+ and Au3+ are in solution. There is no Be or Au. Moreover, both of these cations WANT to become reduced. The Be2+ *wants* to become reduced MORESO than the Au3+, however, the Au3+ can't lose any more electrons.

Please help me understand this basic challenge. The V for the above is E= +2.99, by the way.

 

[Rabolisk]

I advise that you go back and review electrochemistry. What makes you think that there is no Be or Au? Typically, electrodes themselves are the solid, or the solid is coated on the electrodes. In the case of gases, they may be bubbled in. You are correct in that Be2+ wants to be reduced more so than Au3+. However, what you have to realize is that E values are relative. 0 was arbitrarily decided as the value for the standard hydrogen electrode. Just because a reaction's reduction potential is negative doesn't mean that the opposite can't occur, for example. Now, the Be2+ wants to be more reduced, so that will be the reaction that occurs at the cathode (reduction). Naturally, that means that Au has to be oxidized to Au3+ at the anode. The V for the above would be 0.41, because Ecell = Ecathode-Eanode. The higher value is always the cathode.