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Re: EDTA and light.

To: Aquatic-Plants at actwin_com
Subject: Re: EDTA and light.
From: toado <toado at ihug_co.nz>
Date: Tue, 18 Mar 1997 21:02:31 +1200
References: <199703170839.DAA17786 at looney_actwin.com>

> > to 1 ratio.
> > One other point, EDTA degrades in the presence of light so should be kept
> > in a dark bottle.
> 
> Iron:EDTA degrades in the presence of light due to photchemical
> reactions.  Sodium salts of EDTA are perfectly stable in the light.
> 
Uhm, Sodium Edetates do degrade appreciably if you chuck a little UV
light at 'em. Lab suppliers package the stuff in opaque plastic or amber
glass bottles for this reason. As for Iron(2)[EDTA] changing to Iron(3),
most redox reactions speed up wonderfully with a little light of the
right wavelength. However I think this has more to do with the complex
changing the redox potential making the oxidation much more favorable.
The Co(2)->Co(3) system is an easy experiment. Add say ascorbic acid
'antioxidant' and place in the dark for a week or two. The standard
redox potentials indicate no reaction should take place. You'll find a
lot of Co(3) produced.

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