Re: Potassium Oxalate

From: Sandy King <sanking@clemson.edu>
Subject: Re: Potassium Oxalate
Date: Wed, 15 Sep 2004 18:34:41 -0400

> But what about long term storage of potassium
> oxalate solutions? Does the pH change over time?
> I ask because I have an old bottle of the stuff,
> stored partially full in a glass bottle, and
> when I checked it the pH was over 8. Is it to be
> expected that the pH increases with time, and if
> so, should this be of concern?

Did you make that batch in the same way with carbonate?

I'd do a quick check. Mix a batch, keep some aside in a closed
container at room temperature (20-25C). Warm up the other for several
minutes and let it cool down to the room temperature. Does the warmed
version have significantly higher pH now? (But be careful to measure
the pH of the solution at room temperature after warming, that is,
cooling is necessary.)

I suspect that the acidity you are seeing is partially due to carbonic
acid. In some time, the carbonic acid will equilibrate with CO2 in
air that is in contact, that is, leave the solution, and thereby
reducing the acidity of the solution. Warming the solution will
quickly remove much of carbonic acid from the solution.

This happens with other acids as well, for example making sodium
acetate from acetic acid and sodium carbonate/bicarbonate. Use
potassium hydroxide if you don't want this effect.

--
Ryuji Suzuki
"You have to realize that junk is not the problem in and of itself.
Junk is the symptom, not the problem."
(Bob Dylan 1971; source: No Direction Home by Robert Shelton)