[neal_mcg]

Hey,

I am currently trying to dissolve 3.45g EDTA powder (Sigma Aldrich >99% for complexometry) in 1L of  deionised Water. From previous experience I am aware that the solution should be at pH 8 before addition of the solid. However after a few attempts there seems to be no progress with the dissolving.

I first tried adding the EDTA with no pH altering, and as expected most of the solid remains. Then i tried altering the pH to 8 (addition of NaOH) and adding all of the EDTA in one go, this was stirred over night and again the majority of the solid remained come the next morning. Finally i tried altering the pH to 8, adding 0.5g of the EDTA then altering the pH back up to pH8, adding the next 0.5g and so on until all the solid was added, again the solid has remained although this time less than previously.

Does anyone have any experience working with solid EDTA or advice on how to get it to dissolve?

[Arkcon]

Yes.  What you've described always happens to me.  EDTA is an organic molecule, and not very water soluble.  Disodium EDTA is much more soluble, and its what sort solution you're making when you add NaOH.  The tetrasodium of the tetraacetic acid ( did you notice the name if the Edd-tah you've been working with?) is easily soluble

So dont shoot for a particular pH, match the molarities.

[Babcock_Hall]

My experience is that even the disodium salt of EDTA at 40 mM produces a pH that is less than 8.