[atom145]

For a project involving standardising sodium hydroxide solution with analar oxalic acid I have had to make up a 0.1 molar solution of oxalic acid. The oxalic acid used has been in storage for several years (more than 5, I believe) and has formed solid clumps.

My results were inaccurate and I was wondering if the old oxalic acid had absorbed water or somehow reacted after this time. It would explain my results.

I know oxalic acid is a primary standard, but is this a plausible explanation?
Thanks in advance.

[Borek]

Just because it is a primary standard doesn't mean it can't be wet. Correct procedure should start with drying - sorry, can't remember right now in what temperature.

[AWK]

http://www.orgsyn.org/demo.aspx?prep=CV1P0421

[Borek]

http://www.orgsyn.org/demo.aspx?prep=CV1P0421

Making it anhydrous is an unnecessary overkill, dihydrate is perfectly OK (even in some ways better - doesn't absorb humidity from the air so easily, and has a higher molar mass). The only thing is to make sure it has a well defined composition, for most standard substances it means drying for several hour at a well defined temperature.

[atom145]

Thanks for your replies. I should have specified that it was oxalic acid dihydrate already.