Buying the correct caustic soda for soap making

[Joan]

I am curious if it is totally necessary to use 100% pure caustic soda? After a long time searching I finally discovered a wholesaler that sells caustic soda. http://www.sonntagrote.com/english/caustic-soda/ Now I called and the supplier told me that it is only 99% not 100%. But they assured me that it has no other ingredients. With 99% they just refer to the purity. Is that correct? On the other hand it says on their website that this product is suited for soap making.

 

[IrishLass]

99% is perfectly fine. From what I understand from all I've read, NaOH should still be perfectly fine for soap making even if the purity is as low as 96%, and possibly even a little lower, but don't quote me on the "even a little lower" part. Hopefully fellow-member DeeAnna will chime in on that to confirm.

I know that with KOH, a 90% purity is pretty common and perfectly soap-able.

IrishLass

 

[DeeAnna]

^^^ What Irish Lass sez.

I will also add that the purity of a lye (whether KOH or NaOH) from the manufacturer is NOT the purity of the exact same lye as time passes. Every time you open the container and let water vapor and carbon dioxide into the air space, you are lowering the purity of the lye by some small but significant amount.

So don't get too stuck on the idea of near 100% purity. It is not that big of a deal, if for no other reason than it won't will stay that pure for long unless you work in a chem lab with a desiccator cabinet. The NaOH I use is 96% minimum purity (meaning it can range from 96 to 100% as supplied by the manufacturer), and I simply adjust my lye weight accordingly.

Example: I have a recipe that calls for 100 grams of NaOH assuming the lye is theoretically pure (100%) NaOH. But I estimate my lye is only 96% NaOH. How to adjust for the lower purity?

Actual lye weight = Theoretical lye weight X 100 / Actual % purity

Actual lye weight = 100 g X 100 / 96 = 104 grams

 

[Joan]

Thanks IrishLass and DeeAnna!

I will also add that the purity of a lye (whether KOH or NaOH) from the manufacturer is NOT the purity of the exact same lye as time passes. Every time you open the container and let water vapor and carbon dioxide into the air space, you are lowering the purity of the lye by some small but significant amount.

That was my next question!