[Munfred]

Hi

Last class my teacher started talking about electrolysis, the first example was the classical electrolysis of a solution of NaCl in water. To explain how we'd find out the products she went trough a long process involving ions and OH- and metals that were more reactive and less reactive than hydrogen...or something like that. Well in the end she concluded we'd obtain NaOH in the solution and H₂ and Cl₂ at the electrodes.
I then asked her 'but teacher, wouldn't it be simpler if I imagined the electrolysis of molten NaCl obtaining  pure Na and Cl₂ and then though like this: Does Cl₂ reacts with water? No, then I'd obtain Cl2. Does Na reacts with water? Well, then what we get? 2 Na + 2 H₂O -> 2 H₂ + 2 NaOH, therefore we'd obtain H₂ and NaOH at the other electrode. She got a little puzzled with this methoed and we tried it with other reactions, with AgNO₃ the product would be Ag +NO₃ since none of them reacts with water. Then with a solution of ZnSO₄ I concluded we'd obtain Zn at one electrode and either SO₂ or SO₃ and O₂ at the other electrode...and realized the SO₃ (if it was SO₂ it could react with he O₂ anyway) would form...H₂SO₄ in the solution, which would then react with the Zn forming...H₂ and ZnSO₄! And after that I realized the ZnSO₄ would be just a catalyst! Well I know it may not look like much but I kinda concluded that without prior basis, I mean I had no idea that it would be a catalyst until I concluded the   
electrolysis would only be yielding O₂ and H₂

If anyone could tell me if this was merely a lucky coincidence, or if its in fact another way of seeing the same thing (since for the 'common' method I'd need to have that table of things that react or not with the hydrogen and with 'my' method I'd need to know if the product reacts or no with water, it does look pretty much like 2 ways of seeing the same thing)

Well thanks for your Patience reading all this and... oh I almost forgot...the teacher said that in electrolysis of water we'd had H+ and OH- at the electrodes...and well its quite easy to see that they'd pair up to form H₂ and H₂O and O₂...well, could anyone explain me why OH- forms water and oxygen instead of H₂O₂ (which would be pretty nice considering it's properties ;p)


Once more thanks for reading all this and any answers will be greatly appreciated!

[Borek]

its in fact another way of seeing the same thing (since for the 'common' method I'd need to have that table of things that react or not with the hydrogen and with 'my' method I'd need to know if the product reacts or no with water, it does look pretty much like 2 ways of seeing the same thing)

In a way it is another way of seeing the same thing. But: your method requires reactivity series, just like her method, so it in fact boils down to the same... And in reality there is NO sodium metal that later reacts with water. But this is a nice what-if scenario that helps find out why sodium can't be product.

[cliverlong]

Hi
<< cut >>

Well thanks for your Patience reading all this and... oh I almost forgot...the teacher said that in electrolysis of water we'd had H+ and OH- at the electrodes...and well its quite easy to see that they'd pair up to form H₂ and H₂O and O₂...well, could anyone explain me why OH- forms water and oxygen instead of H₂O₂ 

Think about the charge on H⁺ and OH^- and what that means in terms of attraction and bonding to form H₂O

Then think about the charge on OH^- and OH^- and what that means in terms of attraction and bonding to form H₂O₂


What do you conclude?


Note: I have read that in aqueous solution, H⁺ is "carried around" on a water molecule as the H₃O⁺ ion. The reason, I believe, is due to the fantastically high charge density of a single proton and the available lone pairs of electrons on the oxygen in a water molecule to which the proton can bond. How one demonstrates the existence of H₃O⁺ ion I do not know.


Clive

[Munfred]

oh thanks for the answers!

yeah makes sense ;p