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Electrochemical potential

  1. Jul 25, 2013 #1
    I took some phosphate buffer saline(7.4) into a beaker, included a Au electrode and reference electrode (Ag/AgCl) and tried to measure the potential using multimeter. The temperature and pressure is assumable same. The multimeter shows the potential some milivolts but the potential is decreasing like every 2-3 seconds. I thought if temparature and pressure is not changed much it should be fixed..... can someone explain the reason of potential change....
     
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  3. Jul 25, 2013 #2

    Andy Resnick

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    In my experience (Ag/AgCl electrodes) the system needs time, up to a few hours, to equilibrate. Try leaving everything in place (with the power off) for an hour and see if the drift goes away.
     
  4. Jul 25, 2013 #3
    @Andy, thanks for reply. I will try that.....
     
  5. Jul 26, 2013 #4
    still the drifting exists.....can it be the reason that
    The concentration of the PBS (does not contain NaCl) solution is 1M whereas the solution inside the salt bridge is 3 M NaCl.

    If not, i guess may be the ref electrode is damaged some how.....
     
  6. Jul 28, 2013 #5

    NascentOxygen

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    I suspect that the problem with your setup is that your meter is continually drawing current from the cell and causing the cell to become polarized. It's only a small cell, you can't draw current without affecting the potential. Maybe if you only momentarily connect the meter to take a quick reading, then leave it disconnected from the cell for, say, 30 mins, before taking another reading might be an acceptable protocol (but I really don't know).

    A multimeter with much higher impedance may be better, too.
     
  7. Jul 29, 2013 #6
    thanks for the advice....
    today i took new solution, immerged gold and ref. electrode, left them for hour for equilibrium and then took a 5 min reading. again left for another 20 min or so and took reading.....in this way i received better reading....the drift is now 2-3 mv in those 5 mins reading. still acceptable for me.
    But what surprising to me is, after that 5 min reading i disconnect the meter. so when i start taking reading again after 20 mins, the starting potential is lower then before. So my question what exactly was using my cell. as i have disonnected the meter the cell potential should not be used up right???
     
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