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Topic: precipitation and electrolysis of water  (Read 12513 times)

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Offline Borek

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Re: precipitation and electrolysis of water
« Reply #15 on: June 20, 2012, 11:41:43 AM »
Hi Darren, according to Wikipedia it says that a higher potential means more autoionization.

No. If you apply very high voltage it will be no longer AUTOionization, it will be ionization forced by external factors.

And half cell potential has noting to do with that.
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Offline confusedstud

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Re: precipitation and electrolysis of water
« Reply #16 on: June 24, 2012, 01:53:47 AM »
Hi Darren, according to Wikipedia it says that a higher potential means more autoionization.

No. If you apply very high voltage it will be no longer AUTOionization, it will be ionization forced by external factors.

And half cell potential has noting to do with that.

Hi Borek, so higher voltage causes more water molecules to ionize into H+ and OH- ions which then speeds up the process as they are more ions present in the electrolyte which makes it more conductive as the V is higher, R is lower and thus I increases a lot more as well. Hence this makes the process of oxidation and reduction faster than before.

So the key ideas are
1) more ions present equates to more conductive (less resistance) despite whether the ions are reacting or not (like in the dilute NaCl case as shown above)
2) higher voltage means forced ionisation of water which leads to 1) and hence the process of oxidation and reduction becomes faster.

Are these correct? Thanks for the aid given.

Offline Borek

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Re: precipitation and electrolysis of water
« Reply #17 on: June 24, 2012, 07:30:31 AM »
Hi Borek, so higher voltage causes more water molecules to ionize into H+ and OH- ions which then speeds up the process

In a way. But I have a feeling you are misunderstanding the process.

http://en.wikipedia.org/wiki/Wien_effect

Note it requires really high voltages - we are talking about hundreds of kilovolts and electrodes placed millimeters apart. Such a system is on the verge of the electrical breakdown - it has nothing to do with a controlled chemistry.
« Last Edit: June 24, 2012, 07:45:02 AM by Borek »
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Offline confusedstud

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Re: precipitation and electrolysis of water
« Reply #18 on: June 24, 2012, 08:29:40 AM »
Hi Borek, so higher voltage causes more water molecules to ionize into H+ and OH- ions which then speeds up the process

In a way. But I have a feeling you are misunderstanding the process.

http://en.wikipedia.org/wiki/Wien_effect

Note it requires really high voltages - we are talking about hundreds of kilovolts and electrodes placed millimeters apart. Such a system is on the verge of the electrical breakdown - it has nothing to do with a controlled chemistry.

But if I'm talking changing from a 5V battery to a 10V one, will there be a difference? Any why would it be so? Thanks Borek.

Offline Borek

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Re: precipitation and electrolysis of water
« Reply #19 on: June 24, 2012, 10:26:10 AM »
There will be no difference at these voltages.

That is, you can observe a difference if the limiting step is the speed of the electrode reaction, applying some overpotential can speed up the reaction. But the transport is usually diffusion limited and independent of the applied voltage.
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Offline confusedstud

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Re: precipitation and electrolysis of water
« Reply #20 on: June 27, 2012, 08:30:03 AM »
There will be no difference at these voltages.

That is, you can observe a difference if the limiting step is the speed of the electrode reaction, applying some overpotential can speed up the reaction. But the transport is usually diffusion limited and independent of the applied voltage.

Oh so that will cause no noticeable effect at all or will there be a difference?

Also, does volume affect the auto ionisation of water? I think that the greater volume the more the ionisation and if there is a smaller volume of water. But when they are in ions form are they still considered part of the volume of water? Meaning if I have ten water molecules and ten H+ and OH- will the total amount of water be 20 moles and do the ions add volume to the solution? Thanks!

Offline Borek

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Re: precipitation and electrolysis of water
« Reply #21 on: June 27, 2012, 09:09:36 AM »
Oh so that will cause no noticeable effect at all or will there be a difference?

Up to some point there will be a difference, after that increasing voltage won't change anything.

Quote
Also, does volume affect the auto ionisation of water? I think that the greater volume the more the ionisation

No. You need to learn what are extensive and intensive properties.
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Offline confusedstud

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Re: precipitation and electrolysis of water
« Reply #22 on: June 27, 2012, 10:08:32 AM »
Oh so that will cause no noticeable effect at all or will there be a difference?

Up to some point there will be a difference, after that increasing voltage won't change anything.

Quote
Also, does volume affect the auto ionisation of water? I think that the greater volume the more the ionisation

No. You need to learn what are extensive and intensive properties.

I read the wiki on it. So the concentration of the ions will remain the same throughout (0.055microS/cm^3) so as volume drops the the number of ions also decreases so as to get the same concentration?

Also, eg in a solution with 20 H2O with 10 H+ and 10 OH- and another with 10 H2O with 20 H+ and OH- ions. For this 2 solutions is the volume still the same?

Thanks Borek!

Offline Borek

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Re: precipitation and electrolysis of water
« Reply #23 on: August 31, 2012, 12:34:23 PM »
as volume drops the the number of ions also decreases so as to get the same concentration?

Yes, that's the way it works. Number of ions is proportional to the volume.

Quote
Also, eg in a solution with 20 H2O with 10 H+ and 10 OH- and another with 10 H2O with 20 H+ and OH- ions. For this 2 solutions is the volume still the same?

No idea what you mean. Why should the volume be the same?

Also note you can't have arbitrary concentrations of these ions, they react producing water molecules.
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Offline confusedstud

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Re: precipitation and electrolysis of water
« Reply #24 on: September 01, 2012, 03:59:42 AM »
Oh I meant that the 2 solutions have different conditions so in on :larrow:e if them more water molecules form the H+ and OH- ions. So I was wondering if the volume of water includes the H+ and OH- ions.

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