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Re: Oxalate standard electrode potential
- To: Aquatic-Plants at actwin_com
- Subject: Re: Oxalate standard electrode potential
- From: Paul Sears <psears at nrn1_NRCan.gc.ca>
- Date: Tue, 3 Dec 2002 09:25:48 -0500 (EST)
- In-reply-to: <200212020957.gB29vfFA030412 at otter_actwin.com> from "Aquatic Plants Digest" at Dec 02, 2002 04:57:41 AM
> Subject: Oxalate standard electrode potential
> High Paul,
> >Does anyone have a number for the standard electrode potential
> >for oxalate/CO2?
> I looked up in a few old chemistry books in a friend's house, and
> found the values of standard electrode potentials for CO2 and
> Oxalic acid:
> 2CO2 + 2H+ + 2e- = H2C24 (electrode potential is -0.49V)
> H2C2O4 + 2H2O = 2H2CO3 + 2H+ + 2e- (electrode is potential -0.386V)
Thanks. I suggest you keep the voltage pretty low in your
experiments, say less than 2 volts to start with.
> > I really don't think that oxygen evolved at an anode is
> > going to erode the carbon, the claims of the manufacturers of certain
> > devices notwithstanding.
> There was also the following reaction in the book:
> C (graphite) + 2H2O = CO2 + 4H+ + 4e- (electrode potential +0.207)
One can calculate the standard potential for lots of half-cell
reactions - it doesn't mean that they will actually occur. An equivalent
statement is that the free energy of reaction for:
C + 2H2O -> CO2 + 2H2 is 79.9 kJ/mole, which is about right.
The point is that oxygen _is_ evolved, even though the voltage required
is higher than that theoretically needed for the production of CO2.
> There was also another reaction listed in the electrode reactions
> section, which I thought might also be used for cheap electrolytic CO2
> CH3OH + 2H2O = CO2 + 4H+ + 4e- (electrode potential +0.207V)
There is something wrong here - this doesn't balance. Once again,
how would you get the reaction to go?
> Do you think CO2 can be produced by electrolytic oxidation of
> methanol, perhaps in H2SO4 solution? Or, mabe sugar can be oxidized
> too, again with H2SO4 for electrolysis? This may become another
> sugar-based CO2 generator :), but much more controllable compared with
Don't forget that neutral species (alcohols, sugars) have no reason
to go to the electrode and take part in reaction. Methanol _is_ used in
certain fuel cells, but that is a different story....
Paul Sears Ottawa, Canada