Lye Fumes

[topofmurrayhill]

Here's a hint -- Raoult's Law.

Actually, that would not be relevant to the question. It would apply to a mixture of volatile liquids. In this case we have a volatile solvent and a non-volatile solute, which by definition produces a vapor composed of only the solvent. There is no evaporation of NaOH any more than NaCl would evaporate from a cup of salt water.

During and just after dissolution of the caustic, lye droplets get into the air via an entirely mechanical process. Those droplets essentially spray from the surface with the same composition as the solution.

 

[ngian]

Lean back and stir at arm's length with my head turned. Works a charm.

I do much the same except that I do it in the sink with no opened window or ventilation. Most of the times it is from 70gr to 150gr NaOH that I dissolve in twice the water amount. I wear only goggles and I see a few fumes arising at arm's length in front of me and while I breathe with caution only from my nose, if I smell a tiny amount of Lye fumes I then turn my nose on the side until the air is clearer.

 

[Sonya-m]

I used to do it by the hob with the extractor fan on but someone (on here I think?) said they had been doing the same and when they went to clean the filter the metal mesh inside had started to etch away - presumably from the lye

So now I stand my jug in the sink, covered with a paper towel and turn away from it

 

[Susie]

I get far more "steam/fumes/vapors/whatever it is" when I mix NaOH than KOH. This could either be due to the Na or the fact that I add all of the NaOH at once to the water, and KOH gets added slowly and stirred constantly until completely melted.

 

[topofmurrayhill]

Yesterday I made a 40% concentration lye with some vinegar to create sodium acetate. The temperature of the solution peaked at 212 F because of the extra heat from the neutralization reaction.

After a few minutes of mixing, the solution became clear and was still MUCH hotter than the peak temperature most people get after simply dissolving caustic. At that point I was able to take a deep breath from the mouth of the container with no problem at all. As expected, you get pure water vapor regardless of temperature.

The fumes are only formed when you are stirring in the caustic. The surface of the liquid is being physically disrupted, probably by bubbles of hot gas breaking the surface, causing lye droplets to spritz out. The fumes stop when the chaos subsides and you have a clear solution.

 

[LoveOscar]

I don't have as tough a time with winter temperatures in the midsouth as my neighbors to the north would. I always mix my lye on my front porch. I don't particularly want strong lye solution going down my drains if I have to dump it. If it burns the weeds in the yard, oh well. I can use the water hose to dilute it better than my tap probably could.

 

[dibbles]

I don't have as tough a time with winter temperatures in the midsouth as my neighbors to the north would.

Exactly - right now (11 AM) the temperature is minus 10F. Additionally my soaping space is in the basement and I don't want to transport the lye water up and down the stairs. Half of the basement is unfinished, with a door to close that space off so I hold my breath and stand at arm's length to mix the lye into the water. It is really my only option unless I want to carry everything up and down from the basement every time I want to make soap. After the lye has cooled to soaping temp I don't notice any fumes.

 

[LoveOscar]

I soap in my kitchen no problem. I just mix the lye outside because I cannot open my kitchen windows.