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Re: oxalic acid

> From: Vahe Ganapetyan <vahe at hotbox_ru>
> Subject: Re: Oxalic Acid
> Thank you Paul, Bill, Elie for responding. Your comments are very
> valuable.

	I hope it turns out that way.....    :)

> I actually have a graphite electrode lying somewhere in the
> house, I think it is the old-style theatre lighting arc electrode, a
> long bar with the diameter about 0.5", so I'll give it a try as the
> anode. Doesn't have much surface compared with the originally used
> stainless steel plate, but would be useful for corrosion tests (I fear
> though that the oxygen appearing on the anode from decomposition of
> water would erode it - like in the Nisso electrolitic CO2 device...

	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.  Nevertheless, we want to avoid the production
of oxygen as a competing reaction.  The two pKa's for oxalic acid are
pretty low - 1.3 and 2.1, so I would suggest keeping the pH near 3.
That will mean that the oxalate ion concentration will be high, and
the OH- concentration very low (10^-11M). 

	Electrolytic reactions in which gases are produced are notorious
for having high overvoltages (i.e., you need more than you think, based
on calculation), but I suspect that the 5 volts you have been using
is overkill, and would be more inclined to cut it two 2 or 3 to start
with.  Stirring the solution will help prevent what is called concentration
polarisation, which is where one gets depletion of the ion one wants
near the electrode.

	On the electrode erosion topic - one might get mechanical erosion
of the carbon by forming bubbles.

> Besides, a friend of mine, who was involved in prostetics once, has
> promised to give a small titanium rod for experimentation.
> I will continue the tests during the weekend and will write back to the
> list in a few days.

	Does anyone have a number for the standard electrode potential
for oxalate/CO2?

Paul Sears        Ottawa, Canada