Hi, first let me apologise if this post initially seems a little dumb, but please bear with me.
I'm really struggling to understand the reactions taking place at the electrodes during electrolysis. Don't get me wrong here, I've read and researched, but I am unable to find a satisfactory answer. I do get answers, yes, but none seem to precisely answer the nitty-gritty of my posed questions. I'm not well educated in chemistry, so my lack of understanding may well come down to my own ignorance. I'm rather hoping someone here can put me out of my misery.
Electrolysis of pure water seems straight forward enough. If we have 2 platinum electrodes immersed in pure water, and drop 2 volts across the electrodes we get the H+ ion reacting at the cathode and -OH ion reacting at the anode, with hydrogen and oxygen evolved respectively. With pure water being a very poor electrolyte, relying solely on ions produced by self-ionisation, the amount of gases evolved is very low. This is all straight forward and makes complete sense to me.
So now a compound is added to the pure water that makes for a good electrolyte, in this case Na2SO4, which provides the ions 2Na+ and SO4-2.
Now, here's the thing, many people just tell me that because we now have an abundance of charged species in the solution, much more current can flow. They often say this as if this statement explains everything. However, when I push for greater detail and ask tougher questions, if they answer at all, they usually can provide me with no satisfactory answer.
I am told that, in the above case, the electrolyte acts only as a catalyst and takes no part in the reactions at the electrodes. So what exactly do these ionic species do? They may be charge carriers, but what good are they if they do not react at the electrodes?
This is where I'm struggling, this is what I just can't get my head around.
Could it be that the Na+ ions are in fact reacting at the cathode, taking an electron and becoming sodium, which then instantly reacts with the water molecule to produce hydrogen and sodium hydroxide (H2 + 2Na+ +2OH-) ? But then what precisely is occurring with the SO4-2 at the anode?
If on the other hand, we still simply have H+ and OH- ions reacting at the electrodes, what is the point of the electrolyte? And furthermore, if they themselves are not taking part in reactions at the electrodes, why don't the sodium and sulphate ions act to polarise the electrodes and so serve to inhibit further electrolysis?
I mean, if the anode is surrounded by countless sulphate ions, effectively forming a negative barrier - ions that are not going to take part in any reaction - why doesn't everything simply grind to a halt.
I'm hoping that I'm missing something fundamental here because the more I consider this, the more baffled I am becoming. Thanks in advance for any useful input.
Farrah
NB. If I've posted in the wrong place, please feel free to move this post to a more appropriate place.