Sciencemadness Discussion Board

NaOH question

Blind Angel - 3-11-2003 at 09:34

Last years i stole a small NaOH pellet. It was stored in a small pill container (somethng very near) then i put it on my shelf. Strangely it started to become all wet and all the pellets became sticky and when i take one away (not with my hand) it leave a trace on the container, i know this is not the best place to store NaOH but is it possible that the pellet took the humidity from the air (since the container isn't air thigh) and started attacking the plastic or something like this...?

rikkitikkitavi - 3-11-2003 at 10:09

solid NaOH absorbs moisture, and when wet reacts with CO2 in the air to Na2CO3
, probably leaving the trace


Blind Angel - 3-11-2003 at 10:14

Arf! :(
Can i reheat it to anydhrous? I'll use a better container i think....

All Good guesses!

PrimoPyro - 3-11-2003 at 10:58

Very smart guesses, they are all correct in fact.

NaOH is said to be hygroscopic, which means it hs an affinity for bonding with water so strong that it actually rips water molecules right out of the air. NaOH also happens to be on the borderline of what is called deliquescence, which is absorbing water fromair to the point that some degree of solvation takes place. Some molecules are extremely deliquescent, such as thorium nitrate, which is a solid that will completely dissolve itself in liquid about 1.5 times it's own volume, forming a clear solution. I discovered this because I thought it disappeared and the "water" was condensate because it was cold.

Anyways, NaOH will reactin very small amounts with CO2, and moreso in the presence of water, but remember that the concentration of CO2 in air is less than 1%. That will make for a slow reaction, and if it's in sealed container, I don't think it turned to carbonate.

So in most cases, yes you can heat it untilit becomes anhyrous again. But alkalai hydroxides do also attack some plastics, depending on what the plastic is made of. Polystyrenes are fairlyinert to room temperature NaOH, as are polyacrylates, but....

Many cheap tupper-ware-like plastics and similar disposable containers like plastic coke bottles, are a polymeric ester of terphthalic acid and a diol, and aqueous NaOH certainly attacks them. Some plastics have high activation energies that result in no reaction unless high temps are in place, but others have lower energies.

Nothing I've said is cause for worry. I just figured someone might want to knowmore about what's going on in this situation.

To get your NaOH back:

1.Scrape as much of your goop out of the container (try not to touch it bare handed, NaOH hurts) and put it into a glass or porcelain container. The smaller the better.

2.Slowly add some cool water to your goop, and let it dissolve. I say slowly because even though the NaOH is hyrated, it is not fully solvated, and it will still likely heat up upon addition of water. If you dump water in there too quickly,somemy splash back out, carrying hot NaOH into your eye. Not cool.

3.Anything that is still goopified in the dish, break it up if youcan with somesort of inert utensil. Personally I don't worry about such little side reactions as stirring with a wood spoon, but for you,you hve a small amount of NaOH and you don't want to react it all away into nothing. If you don't have any glass stirring instruments, and you want to be anal, then take a tensil and put a latex glove over the part you are going to submerge, then poke at anything that isnt dissolved. Try to break it up.

If it won't break up, it's likely something you don't want anyway. Keep in mind before yougo poking around, that the solution may very well be hot so be aware.

4.Put a little H2O in your original plastic container, again not looking right at it so if it crackles it won't go in your eye. Swish it around a bit,then dump the water into your other solution you've been poking at.

5.Remove anything not dissolved in the solution and toss it.

6.Boil away the water in something that has a small volume but also a small surface area at the boiling surface. It's a pin in the ass to have to recover powder as a thin film on the bottomof a large container. It will boil slower this way, but its easier to collect afterwards.

I suggest keeping it in aglass container, a very small one at that, maybe with a small bag of silica gel taped to the lid, and airtight seal it.

I get the feeling you don't hve a lot of lab experience, so if I'm wrong, please don't take offense to the detail of my post. Others my try similar things, and I wouldn't want someone not skilled in the laboratory to get hurt from simple things hat can easily be avoided.


Blind Angel - 3-11-2003 at 13:16

Thanx for your very (a bit more than needed) detailled post. I don't have a lot of lab experience but i could have been able to figure the reste myself :D. Thanx a lot. BTW: why do i need to disolve it completly, i could simply heat up the pellet that i have up to 100°C so water will evap, no?

PrimoPyro - 3-11-2003 at 13:24

I specified todissolve as much as you can because Ihavent looked at it myself. Theres a chance that it has eaten a little of the plastic, and itmight be pitted inside.

I was just thinking you would still want all you NaOH back, and the easiest way to reclaim it is tosolvate it, since the plastic will be left behind.

Blind Angel - 3-11-2003 at 13:30

ok I see, thx again :)

Marvin - 3-11-2003 at 14:15

You can usually buy this quite easily as a drain cleaner, and this also provides you with a container.

If you buy some, I would advise thowing out what you have, as its most probably more contaminated than what youd be buying.

Dont store it in a glas container, as NaOH attacks glass (fairly slowly).

Dont store it with silica gel crystals in the bottle, becuase being a better dessicating agent the NaOH will eventually draw out all the water in the crystals.

Dissolving is it pointless, as if the bottle is polyester of somekind the products of the hydrolysis will both be water soluable.

Latex gloves will provide some protection, but they do seem to be eaten by most common reagents/solvents, so watch out. Polyethylene gloves are normally better for acids/alkalies.

Putting a glove on then poking the mixture is dumb. Use a metal utensil, such the thin end of a stainless steel spoon. Make sure its washed very well afterwards.

Whatever touches the NaOH, particulaly when hot must not be glass, or aluminium, or zinc. Wood is not a good idea, neither is pottery.

'Not looking right at it' is furthur dumb. Get eye protection. Goggles for using power tools will be fine in the short term and watch

Getting NaOH on the skin is unlikley to hurt at first, youre more likley to notice that it feels wet/soapy as it starts to saponify the surface of your skin, wash off with plenty of water right away and its no big deal.

If these precautions seem over the top, its becuase NaOH is nastier than you think it is.

Blind Angel - 3-11-2003 at 17:57

I know I know how nasty is NaOH.
I live in an indrustrial city that specilize in Aluminium Extraction/Transformation so in the factory there are big container of Caustic Soda, rumor says that 3 worker where flooded by it when an accident happened. The rumor also specifiy that it was the first time that a scream could be heared in all the factory which take more than 15min to go from one side to an other by walking.

ech310n - 3-11-2003 at 18:42

Marvin, are you sure that NaOH attacks glass? I can't find any mention of that in an MSDS I have. I've been washing out some of my good flasks with NaOH because it cleans so well :o

BromicAcid - 3-11-2003 at 18:58


are you sure that NaOH attacks glass?

Yes, slowly if it is dillute and cold but somewhat more rapidly concentrated and hot. Molten sodium hydroxide will do a number on glass. Because of this storing sodium hydroxide in glass is not done at my college, it's in HDPE containers.


PrimoPyro - 3-11-2003 at 22:59

I specified the nuances that I did because it was my assumption that the individual did not have any lab equipment whatsoever, and I wasn't going to instruct him to go buy this and that to reclaim 50g of NaOH.

Also, about the ltex glove, you misinterpret me. I did not say to wear the glove and poke it. I said to use a utensil and thread that into a glove, such as the finger. If you stick true silverware into aqueous NaOH you will eat the silverware. Not something to make mothers happy.

I said that personally I don't care about a little whitening of a wooden spoon, but this is just me. I also don't care to just lose the 50-100g NaOH.


OT question

Organikum - 4-11-2003 at 07:22

PP, do you still make acetaldehyde from ethylene glycol so easy by some dil.H2SO4 pinacole rearrangement as it is done at the HIVE all day?

nice to see you back, btw.
cook your soup on your own flame better...


Thanks for the cehap shot, Orgy

PrimoPyro - 4-11-2003 at 10:00

Love you too Orgy.

PP, do you still make acetaldehyde from ethylene glycol so easy by some dil.H2SO4 pinacole rearrangement as it is done at the HIVE all day?

Only theory, and you know that. BTW I still believe this can work, and I'm not the only one thinking so. If it weren't for unforseen circumstances there might have been a writeup of factual data by now.

Thanks for the confidence....


Marvin - 4-11-2003 at 17:57

To remove most of the water from NaOH it usually needs fusing or at the very least, neer fusion tempoeratures so wood is certainly out of the question.

I apologise for missinterpeting the latex glove thing, but I think it wont work.

If you put silverware into the mixture I dont see why it would be attacked.

Acetaldehyde can be made from ethylene glycol, I bilieve there is a process that involves distilling from zinc chloride. I dont know the best conditions or the yeild, but it does work. Given the large difference in boiling points it certainly has potential. I suppose technically you could call this a pinacol rearangement, but then you could also call it a dehydration.

Blind Angel - 30-11-2003 at 10:19

I dit try you method:

Took all the NaOH i ha, put it in a pan, and dissolve it entirely in water (high dissolution heat btw), they i made it boil. Started the fan to suck vapour.
Some time after i got a circle of little powder around the pan, i scraped them it was NaOH that came out during the boiling, i was able to see smal particule jumping out of the water. Once all the water evap. a layer of NaOH was left, i stirred this layer with a spoon to make sure no water was left in. To my big suprise, the andi-adhesive layer of the pan went off while stirring (not scraping), i had to remove it. Once all the NaOH removed from the pan i had the surprise to see that it was starting to eat trough the metal (see picutre).

105-0566_IMG.JPG - 200kB

Saerynide - 30-11-2003 at 10:25

WOw, about how much pure NaOH was that?? :o

Blind Angel - 30-11-2003 at 10:47

The purest i could have (lab grade)

unionised - 30-11-2003 at 13:48

Did you not know that reasonably strong bases will dissolve aluminium?

vulture - 30-11-2003 at 14:15

I think he's referring to PTFE, Teflon layer inside the pan. Unfortunately that's not stable towards alkalimetal bases.

Blind Angel - 30-11-2003 at 14:51

well, the in fact the two, i think the teflon has been attacked, then the aluminium

unionised - 1-12-2003 at 13:54

Were there little black bits of teflon floating in the solution when you finished boiling?

Blind Angel - 1-12-2003 at 15:11

No, the NaOH left a crust like ½cm thick in the bottom, but i remember having scraped some black while trying to get the NaOH that was on the border of the pan...

unionised - 1-12-2003 at 15:43

I asked because, while molten alkali metals and their hydroxides will attack teflon the solutions generally will not. OTOH if there are any pinholes or scratches in the teflon and the NaOH gets through the H2 generated will lift the plastic layer.

Blind Angel - 1-12-2003 at 17:48

I think this would be the most probable explanation, that or it's wasn't a teflon coating in the pan. I was pretty surprised that it was attacked since i remember that we used teflon coated stirred in a lab involving strong alkali base.

unionised - 2-12-2003 at 15:41

I thought it was a plausible explanation; that's why I posted it.