5 replies to this topic

[Richard H]

Okay I'm going to make some sodium oxalate for yellow glitter, and I think the easiest way to do it is:

Na2CO3 + C2H2O4.2H2O -> Na2C2O4 + CO2 + 3H20

I presume light heating will help drive the reaction to the right with carbonic acid forming CO2 and water leaving pure sodium oxalate in solution. What would be the best way to ensure all the oxalic acid is converted to the oxalate, use an excess of sodium carbonate and then recrystallise a couple of times?

[paul]

We did this to make Strontium Oxalate...
To make sure all the oxalic acid is converted, we use an exess of SrCO3. A magnetic stirrer is VERY helpfull to this reaction, even better when you?ve got an heated stirrer. It produces much CO2 and a dusk mask is absolutely neccessary, too.

greets,

paul

[Richard H]

I cross posted this to rec.pyro, and Mike Swisher was very kind to remind me that an excess of sodium carbonate would be bad as it may cause alkaline reactions in compositions with aluminium. Instead I should add a slight excess of the oxalic acid.

I will test the solution with litmus paper and try to get the pH as near to 7 as I can.

[JamesH]

Is the oxalic acid sold as 'wood bleach' the dihydrate or the anhydrous form? I've done a fair bit of research but didn't really find what I was looking for.
I suspect it is the dihydrate, does anyone know otherwise?

Richard, did you have any success with the sodium oxalate synthesis?

[paul]

Some Art stores carry it:
http://kremer-pigmen...g/ebindem03.htm

Kremer?s datasheet says that the oxalic acid used for bleaching leather (I suppose its used for wood then, too) is the .H2O form...
It?s cheap stuff, only USD 5,45 / Kg ...

[Mumbles]

I suspect the wood bleach is the dihydrate. It's more economical to sell that way.

One way to check would be a titration of sorts with calcium chloride. Make a solution of the calcium chloride, say 20g. This is between .1 and .2 mol. Add 5g of the oxalic acid in question(.05 to .03 mol). The oxalic acid is thus the limiting reagent. The Calcium oxalate is extremely insoluble. Filter and wash with water 3 times. If you have around 8g you have the anhydrous. If you have 5.5-6g you have the dihydrate. If you're trying these calculations and getting something different I based the final yield on calcium oxalate monohydrate.


I've made some Sodium Oxalate. However all my sources of Oxalic acid are too expensive to make it economical. It's cheaper to buy the Na2C2O4 than make it. If I purchased in bulk, it would then be cheaper.


[edit] Just checked one supplier and it would be a lot cheaper to make it myself. It's around $1.10 a pound, maybe a little more when including dH2O and such. Better than the $5-12 that is being charged right now.

Edited by Mumbles, 23 October 2006 - 09:00 PM.