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Why is salt needed for electrolysis of water? - Printable Version

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Why is salt needed for electrolysis of water? - Leonhard - 04-12-2018

Hello all.


I'm starting to learn about electrochemistry and I want to make sure I fully understand the concept of electrolysis and electrolytic cells. 

For the electrolysis of H2O into H2 and O2 I understand that we have the two half-reactions:

2H+(aq)+2e−⟶H2(g)E∘red=0.0 V
2H2O(l)⟶O2(g)+4H+(aq)+4e−E∘ox=−1.23 V
I have this mental model in my head where the reduction reaction at the cathode is being supplied electrons by the power source and the oxidation reaction at the anode is supplying electrons that are "sucked up" by the power source (and transferred to the cathode). 

What I don't understand is why a salt like NaCl is required. I know the conductivity of water is poor, but why does it need to conduct electricity? Isn't the circuit completed by the ionic current of the H+ ions?

Could it be that the conditions local to each of the electrodes change enough to make the half reactions more and more unfavorable (which NaCl somehow helps with)? 

Any help in understanding would be very appreciated! Thank you all!!