Lye Fumes

[AustinStraight]

What exactly are the fumes? I've noticed "fumes" coming off of the lye solution, but I'm honestly starting to think it's just water vapor. I was on a soap-making video where the soap-maker urged others to keep a safe distance from the lye pitcher because it would give off fumes. Someone commented and said that sodium hydroxide + water creates heat, and the fumes are really just water vapor, perhaps with a small amount of sodium hydroxide.

This forum makes me even more confident that the fumes are just water vapor. One chemist on that thread said, "If it's NaOH in water you shouldn't get any fumes at all, unless you are dumping mass quantities of NaOH into a small amount of water, and then perhaps you might get aqueous NaOH in water droplets vaporizing." What do you guys think?

 

[osso]

The fumes are potent and can be caustic. Ventilation is a must.

 

[Obsidian]

I think its more then just water vapor. I've accidentally breathed in the fumes before and its painful. It burns the sinuses and causes coughing.
The link to the other forum doesn't really answer the question at all, more guesses then anything.

 

[AustinStraight]

That's the thing... I wish I had the equipment to see what exactly it is.

 

[AnnaMarie]

I caught a whiff of these fumes one time, and I'll never forget it. It was only brief, but it made me cough enough to respect its toxicity. Water vapor my foot. I have a water vaporizer for colds and those fumes don't make me cough.
Cheers!
Anna Marie

Oops! I mean water humidifier.

 

[jenfrat]

Definitely more than water vapor. The fumes burn the mucous membranes and are an irritant.

 

[lpstephy85]

Yeah, I remember when I caught my first inhale of lye fumes. I coughed for a good five minutes. Now when I mix, I cover my mouth and nose with a cloth until my water is clear. I don't care what is in the vapors, all I know is that it is something that should not be in you.

 

[jade-15]

One chemist on that thread said, "If it's NaOH in water you shouldn't get any fumes at all, unless you are dumping mass quantities of NaOH into a small amount of water, and then perhaps you might get aqueous NaOH in water droplets vaporizing." What do you guys think?

Thats the answer.
We ARE dumping mass quantities.

At one stage I saw NaOH available in a molar solution - and 6 mol solution (which is stronger than is allowed in high school chemistry) requires 240g/L.
Quick look at soapcalc and we are making lye solution around 11M (using 38% water). Incredibly strong, what I would call mass quantities.

Also, initially I found my lye water/milk was not heating up as I slowly added my lye to solution... then I watched some videos and my 'slowly' is very different to the videos. To me, "slowly" meant like in chemistry, add a spoonful, stir until almost dissolved, and repeat... the videos did it more like "slowly" in cooking. Started doing this and I got fumes as well as heat.

 

[DeeAnna]

Water VAPOR by definition is not visible -- you'd have to be able to see individual molecules in order to see actual water vapor. The visible MIST rising from your lye solution is a cloud of tiny droplets of the sodium hydroxide solution, not just water vapor.

 

[Neve]

Even the slightest whiff of that stuff has me coughing. It really irritates my throat so I usually wear the mask as well as have the exhaust on full blast and have then jug as far away as I can while I'm doing the oils.

 

[Silverwolf]

The reason the vapor is so nasty is because it's a aqueous solution of naoh, basically your inhaling lye water which of course is a irritant.

 

[The Efficacious Gentleman]

As others have said, it's semi-gaseous lye solution! Imagine how that would feel on the inside of your throat. Now imagine when you have a deep cold and you put your head over some steam with some nice healthy things in there. Now image those two things together...................................but without the healthy things in the steam!

 

[karenbeth]

It's very dangerous and could cause serious lung problems if you don't take precautions

 

[MagicalMysterySoap]

Those fumes are nasty and make me cough horribly. Now I freeze ALL of my liquids into ice cubes and don't get any fumes at all when I mix them with lye.

 

[AustinStraight]

Thanks for all the responses It still doesn't make much sense to me though... minerals are separated from water by distilling the water (evaporating the water & capturing the water vapor), you wouldn't think there would be lye in the water vapor.

 

[DeeAnna]

"...minerals are separated from water by distilling the water (evaporating the water & capturing the water vapor), you wouldn't think there would be lye in the water vapor...."

Wrong.

First off, you are assuming "hard water" compounds in water behave the same as sodium hydroxide in water. It is incorrect to think these two solutions will behave identically. For one thing, magnesium and calcium compounds in hard water are extremely dilute. The NaOH solution we make for soap is highly concentrated, as Jade pointed out.

Second, your chemist acquaintances are apparently not well read on the physical properties of NaOH solutions. The vapor pressure of NaOH in solution is low -- 1.5 mmHg @ 68°F for a 50% solution* -- but it is NOT zero. This means there will indeed be sodium hydroxide vapor in the air above any solution of sodium hydroxide. Vapor pressure goes up as the solution concentration increases and as temperature increases, so a hot concentrated NaOH solution such we make for soaping will have a higher NaOH vapor pressure, compared to a cool dilute NaOH solution. *See http://www.dow.com/causticsoda/offer/physical.htm

Third, evaporation is not the only method of transporting material from the liquid phase into the gaseous phase. In the case of making a lye solution for soap making, Jade is right -- we're dumping large amounts of NaOH in water and getting a large, fast evolution of heat. This is generating MIST as well as VAPOR. A mist is a mass of liquid droplets, not individual molecules. The mist from a hot lye solution is even more of a health hazard than the vapor.

 

[jenfrat]

DeeAnna-as a former chemistry teacher can I say that I love to read your responses.

 

[AnnaMarie]

DeeAnna-as a former chemistry teacher can I say that I love to read your responses.

You've just outed yourself! Now we know who else to bother for scientific input
Cheers!
Anna Marie

 

[AustinStraight]

Wow! Thanks, DeeAnna!

 

[grayceworks]

And for a demonstration of the caustic nature of the fumes which does not involve inhaling -- which I can assure you from experience is a 'Very Bad Idea' to quote Jurassic Park -- just take a look at the aluminum vent filters in your stove hood after a few months of making your lye-water on the stove with the vent fan running lol