1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The Persulfate-Sulfate Couple

  1. Oct 5, 2014 #1
    Hi. I have a lab that concerns this reaction as follows:

    S2O8 2- + 2e- = 2SO4 2-

    Can anyone give me a hint as to why this reaction would NOT (and indeed does not as found in the lab) have a potential of ~ 2V from the H+/H2 reference? What is preventing the reaction from reaching its maximum?

    Attempts:

    1) I've tried looking at http://hyperphysics.phy-astr.gsu.edu/hbase/tables/electpot.html and figuring something out but nothing seems to work. No extra information is given.
    2) Is equilibrium reached?

    Thank you.
     
  2. jcsd
  3. Oct 6, 2014 #2

    Borek

    User Avatar

    Staff: Mentor

    2.1 V is a normal potential, what did you put in the solution and in what concentrations?
     
  4. Oct 6, 2014 #3
    Hi Borek. The ions above are added via 0.1M K2S2O8 and 0.1M K2SO4. Thanks.
     
  5. Oct 6, 2014 #4

    Borek

    User Avatar

    Staff: Mentor

    And what is the measured potential?
     
  6. Oct 6, 2014 #5
    1.7V relative to Cu/CuSO4.
     
  7. Oct 6, 2014 #6

    Borek

    User Avatar

    Staff: Mentor

    And what is the standard potential for the Cu/Cu2+ system?
     
  8. Oct 6, 2014 #7
    It has a standard potential of +0.34V.
     
  9. Oct 7, 2014 #8

    Borek

    User Avatar

    Staff: Mentor

    So what is the potential against hydrogen electrode?
     
  10. Oct 7, 2014 #9
    It is 2.1V
     
  11. Oct 8, 2014 #10

    Borek

    User Avatar

    Staff: Mentor

    So where is the problem you've mentioned in the very first post?
     
  12. Oct 8, 2014 #11
    My question was "Can anyone give me a hint as to why this reaction would NOT (and indeed does not as found in the lab) have a potential of ~ 2V from the H+/H2 reference? What is preventing the reaction from reaching its maximum?" Perhaps I wrote it in a "too-wordy" style. I simply meant that I need help understanding why this reaction does NOT have a potential of ~ 2V from the H+/H2 reference (as measured, it actually has a potential of 0.5V).
     
  13. Oct 9, 2014 #12

    Borek

    User Avatar

    Staff: Mentor

    Data you have listed so far suggest something else, I don't understand what you are talking about.

    What was the procedure you followed? What have you really measured?

    If you have measured the potential to be around 1.7 V against Cu/Cu2+, it is equivalent of measuring it as around 2 V against hydrogen electrode. Now you are telling us it had 0.5 V against hydrogen electrode. For me that means that either the signal hydrogen electrode is broken, or you are not telling us everything.
     
  14. Oct 10, 2014 #13
    Whoops, think I messed it up. Let me try again:
    Given: rxn has a potential of ~2V relative to standard H+/H2, Cu/CuSO4 reference electrode has a potential of about
    +0.34 V relative to standard H+/H2, so persulfate-sulfate solution should have a potential of around 1.7 V relative to the Cu/CuSO4 reference.
    Measured: ~0.5V relative to Cu/CuSO4 reference.
     
  15. Oct 10, 2014 #14

    Borek

    User Avatar

    Staff: Mentor

    OK, so you measured around 0.8 V against hydrogen electrode.

    Honestly - no idea. Can't think of any reasonable chemical explanation, looks like some fubar case ;)
     
  16. Oct 11, 2014 #15
    Fair enough, I'll ask my Prof. Thanks anyway.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: The Persulfate-Sulfate Couple
  1. Lead Sulfate battery (Replies: 4)

Loading...