EDTA solution becomes slurry

Tom Knight via methods%40net.bio.net (by tk from shaggy.csail.mit.edu)
Sun May 31 16:41:08 EST 2009

Yoram Gerchman <gerchman from research.haifa.ac.il> writes:
> EDTA will not dissolve until pH 8 is reached, hence the "white
> slurry". Simply keep adding NaOH while measuring pH (I suggest using
> a pH paper, not an electrode). When you get near pH=8 you will see
> sudden clearance of the solution. You can definitely start with NaOH
> pellet (add a little and let it dissolve completely before adding
> more) and use NaOH solution only for final adjustment. Preparing
> EDTA solution is a slow process...

To save some time and frustration, you need about equimolar amounts of
NaOH and EDTA to dissolve the EDTA.  Effectively, you are making
trisodium EDTA from disodium EDTA.  You can add almost enough pelleted
NaOH to reach this point, then titrate with pH paper and 5M NaOH
solution to reach pH 8.0.  Just a reminder, you cannot make a 1 M
solution -- the stock solution is 500 mM.

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