Sciencemadness Discussion Board

HCl fuming

mericad193724 - 28-8-2006 at 13:20

I got some 31.45% HCl from a hardware store a few months ago. It is very light green and recently has been FUMING A LOT. I used this in the fall and spring and never had these thick, visible fumes continuously coming from the bottle as I am getting now.

Today was a humid day (rainy and hot) and I wanted to do a titration in the garage so I opened up the HCl and thick fumes were coming off it this because it is too warm or because of the humidity?

Would cooling the bottle to 15C stop the fuming? Dilution?



woelen - 28-8-2006 at 13:53

It is a combination of heat and humidity. Hydrochloric acid is HCl, dissolved in water, and in this state it is ionized to H(+) and Cl(-). The higher the temperature, the less soluble the gas HCl is in water. So, at higher temperatures, the liquid tends to give off more HCl gas than at low temperature.

Another thing is humidity. The gaseous HCl, given off by the solution, partially reacts with water vapor in the air to form a solution of HCl in water. In fact, very small droplets of hydrochloric acid are formed. On a very hot, but dry day, you will notice a strong stench, but you hardly have any fuming.

If these fumes really irritate, then dilute the acid a little. Take 5 parts of acid and mix with 1 part of water, bringing the concentration down to 25 .. 26%. If you do this, then it still is fairly concentrated, but the fuming is MUCH less. Over here we usually buy the acid in 30% concentration, and at that concentration there is quite some fuming, albeit not excessive. I also have some 37% HCl and that stuff is terrible. On warm days, the bottle even is pressurized like a sof drink with CO2 in it. When the bottle is opened, there is a strong hissing noise of pressurized gas escaping from the bottle, and immediately there is a thick plume of HCl-fume. Above 25 .. 26 % the fuming rapidly increases with concentration.

silonyl - 30-8-2006 at 05:21

Great explanation, woelen

I think it's worth noting as well that caution should be exercised around concentrated HCl whether or not it is visibly fuming. That same HCl gas that forms droplets of hydrochloric acid on a humid day will form the acid on contact with moist tissue, such as the mucus membranes of your respiratory tract. This tends to be painful well before it's a serious hazard, but I also know someone who had a cough for weeks after using conc. HCl outside of a hood back in school... so good ventilation and/or an appropriate respirator (acid mist rated) is advisable.

HCl fumes

MadHatter - 30-8-2006 at 21:33

I've noticed that with my 31% acid but not with the 20% version. Both came from hardware
stores. When the weather is colder I don't see visible fuming but my nose tells me that
vapours are in the air. No doubt about it !

HCl fuming

Elawr - 31-8-2006 at 07:32

HCl fumes are even more deleterious to metallic objects, and this is why I no longer store HCl solutions indoors. Even tightly sealed bottles seem to emit minute amounts of corrosive HCl fumes which attack all nearby metal, particularly iron. The Cl- ion is a universal corrodant of metals, any very hard to contain when coupled with the proton. In this way H+ with Cl- aquires volatility as HCl and can actually seep between the polymer molecules of the plastic vessel containing it.

Once I retrieived a well-stoppered bottle of 37% muriatic acid which had been stored in the basement for many months. The outside of the bottle, which appeared to be of polyethylene, was covered with minute dew-droplets of acid. Various iron tools in the vicinity were all severely rusted . Even aluminum, copper, and bass things nearby were corroded. Now that I've banished my hydrochloric acid to the outdoors, I've been able to keep all my tools bright and shiny with no difficulty. I would not keep hydrobromic or hydroiodic acid indoors for the same reason. Hydrofluoric I won't keep at all (I'm too scared of it)!!

Those of you suffering from mysterious rusting and corrosion problems around the lab be advised: there could be some errant container of a halo-acid to blame!

[Edited on 31-8-2006 by Elawr]

woelen - 1-9-2006 at 01:21

Yes, I also noticed this problem. Since that time I also store my HCl outside my cabinet with chemicals. A similar problem exists for HNO3, but to a lesser extent.


MadHatter - 1-9-2006 at 08:06

Elawr, like you, I'm terrified of this compound ! Even some of its most experienced handlers
have been injured/killed by its deleterious effects. I won't even touch this one unless I
have an absolute need !

silonyl - 1-9-2006 at 12:29

The plastic bottle that hardware-store acid comes in is very slightly porous to diffusion of gases, at least small ones like HCl, so there is some diffusion of the gas through the plastic and into the surrounding air. Some probably also gets out around the seal with the cap.

I used to work with elemental iodine a lot (it's absorption/emission spectrum is used as a calibration standard for high-res spectroscopy) and it has such a high vapor pressure that even a closed glass bottle inside of a sealed ziplock baggie would cause nearby metal objects to corrode :o