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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: aeacfm on August 18, 2010, 08:11:40 AM

Title: What does this mean
Post by: aeacfm on August 18, 2010, 08:11:40 AM

a chemical reaction has  a standard electrode potential of a specific value as example

  S4O6 ²⁻ + 2 e−  ::equil::2 S2O3 ²⁻        e^o= +0.08

theoritically 

i read some thing that when i has electrode of the material at standard conditins it will has the value of e^o 

practically when i want to perform the above reaction what e⁰ refere to  ?
 

Title: Re: What does this mean
Post by: aeacfm on August 18, 2010, 08:12:57 AM

also does the sign has importance weither + or -

Title: Re: What does this mean
Post by: MrTeo on August 18, 2010, 11:11:13 AM

If you build a standard electrode based on this reaction (for example you dissolve in water salts with the anions required, with the activities equal to 1, 25ºC and so on), you put a platinum wire in your test tube and you connect it to a standard hydrogen electrode (based on the reduction H₃O⁺/H₂) which has a potential of 0.00 V (this is IUPAC convention), using a good voltmeter you'll see that between the two poles there's a potential difference of 0.08 V (the plus means that your electrode is a better oxidizer than the SHE, so the electron flux goes from the second one to the first one, try writing the half reactions to see what I mean).

Title: Re: What does this mean
Post by: aeacfm on August 18, 2010, 11:31:58 AM

ok thats very good , then when i make the cell reversibile (electrolytic cell ) what e^O mean ?
is it - i require e^O to perform such reaction- !!!!!!!

Title: Re: What does this mean
Post by: MrTeo on August 18, 2010, 03:47:46 PM

Quote from: aeacfm on August 18, 2010, 11:31:58 AM

is it - i require e^O to perform such reaction- !!!!!!!

I see you're easily excitable  ;D

Anyway yes and no: from a theoretical point of view we need at least E⁰ to perform an electrolysis with those compounds but in a real situation more complex factors have to be considered such as the supertensions or the potential drop caused by the cell...

Maybe if you tell us what information you need (="what do you want to do") we can be more specific and clear in our answers...

Title: Re: What does this mean
Post by: aeacfm on August 20, 2010, 05:48:48 PM

dear teo
thank you for your interest , i am not easily excited like you said but onl ywan tto learn (because of  disadvantages in arabs education)
what i wan to do is to make electrolysis to acis to convert it to other form (more reduced form) of it the oxidized from produced in wast water of our plant and specific method to remove it by that method i mentioned

many thanks again for your time