Sciencemadness Discussion Board

Sodium hydroxide versus glass

DoctorOfPhilosophy - 26-7-2012 at 17:22

I've heard a lot of people saying that storing sodium hydroxide in glass will destroy it. To test the idea, I kept saturated aqueous solution in a Pyrex container for 2 weeks, at 23 C, and cleaned it up today. There is no visible or tactile damage to the inner surface as far as I can tell.
So is it only damaging to heat NaOH in glass, or would the glass fall apart if I held the solution long enough. Any ideas?

Vargouille - 26-7-2012 at 17:46

A NaOH solution doesn't harm glass at standard temperatures from what I recollect, but molten NaOH will eat through it, and heated solutions of NaOH may etch the glass.

simba - 26-7-2012 at 18:03

NaOH attacks glass very slowly at room temperature and even at 100-150 ºC from my experience. I've already worked with pure NaOH heated to 150 ºC in glass containers several times, without no noticeable damage.

BromicAcid - 26-7-2012 at 19:18

Quote: Originally posted by simba  
without no noticeable damage.


I don't know if I like the sound of that...

Anyway, amusingly enough if you read through some of the threads on HF experiments you find that people use the 'acid test' of having it attack glass to determine if they were successful in the preparation of that material. Using this criteria their attempts sometimes are failures. However it often comes to pass that later they find that the vessels really were attacked.

The same holds true here. Chemical attack of glass is very uniform, very smooth. It's hard to tell when it occurs. Sodium hydroxide solutions will attack glass, slowly... But you'd never notice it without weighing the bottle, storing, cleaning, and re-weighing after drying.

At room temp you will notice nothing, the reaction is much too slow. For all intents I would consider glass a safe storage medium, if only due to the prevalence of embossed glass Sodium Hydroxide storage bottles that pop up on eBay from bygone eras.

My point is, weight is the key here. The glass might not look attacked if you're trying to force the attack but that will not tell you the whole story.

Doing a cursory search online yielded some numbers from a brochure of glass lined reaction kettles. The brochure gives the following information:
Quote:
At pH = 13 (NaOH 0.1N) this maximum is 70°C. Therefore, it is important to be cautious when using hot alkalis. Temperature must be controlled, as an increase of 10°C doubles the rate of attack of the glass.


It also gives a graph which indicates that a 50% NaOH solution at 55 °C or so will dissolve 0.1 mm of glass per year. Interestingly a 30% sodium carbonate solution under the same conditions will do the same thing.

Endimion17 - 27-7-2012 at 00:08

There certainly is noticeable damage if you try that with volumetric glassware.
"Noticeable" is a vague term. Do you notice the weight of ant's leg? No, but another ant does.

Lambda-Eyde - 27-7-2012 at 06:04

Storing NaOH solutions in glass is perfectly safe as long as it doesn't have a ground glass stopper. It will easily jam those.

polymerizer87 - 27-7-2012 at 06:12

I've found it will etch the glass overtime, but nothing more than what conc. acids will do.

simba - 27-7-2012 at 07:53

Quote: Originally posted by Endimion17  
There certainly is noticeable damage if you try that with volumetric glassware.
"Noticeable" is a vague term. Do you notice the weight of ant's leg? No, but another ant does.


You got what I mean.
Quote: Originally posted by BromicAcid  
Quote: Originally posted by simba  
without no noticeable damage.


I don't know if I like the sound of that...

Anyway, amusingly enough if you read through some of the threads on HF experiments you find that people use the 'acid test' of having it attack glass to determine if they were successful in the preparation of that material. Using this criteria their attempts sometimes are failures. However it often comes to pass that later they find that the vessels really were attacked.

The same holds true here. Chemical attack of glass is very uniform, very smooth. It's hard to tell when it occurs. Sodium hydroxide solutions will attack glass, slowly... But you'd never notice it without weighing the bottle, storing, cleaning, and re-weighing after drying.

At room temp you will notice nothing, the reaction is much too slow. For all intents I would consider glass a safe storage medium, if only due to the prevalence of embossed glass Sodium Hydroxide storage bottles that pop up on eBay from bygone eras.

My point is, weight is the key here. The glass might not look attacked if you're trying to force the attack but that will not tell you the whole story.

Doing a cursory search online yielded some numbers from a brochure of glass lined reaction kettles. The brochure gives the following information:
Quote:
At pH = 13 (NaOH 0.1N) this maximum is 70°C. Therefore, it is important to be cautious when using hot alkalis. Temperature must be controlled, as an increase of 10°C doubles the rate of attack of the glass.


It also gives a graph which indicates that a 50% NaOH solution at 55 °C or so will dissolve 0.1 mm of glass per year. Interestingly a 30% sodium carbonate solution under the same conditions will do the same thing.


Nice to know about that, but I was talking about pure NaOH, not NaOH solution. Pure NaOH will not cause an uniform damage to glass like it will in solution (unless melted of course), and any damage will likely turn the glass surface rough to the touch, and easily noticeable.

Anyway, as the pdf states, the rate of corrosion is pretty slow still.

Antimatter - 27-7-2012 at 11:23

The NaOH must be a molten solid to eat through the glass. Sodium hydroxide solutions, depending on their concentration, may etch or weaken glass if heated.

Your experiment only uses a sodium hydroxide solution at room temperature, and that does nothing to the glass. If you heat it, the glass may be whitened or streaked. If you want to completely destroy the glass, you need to heat sodium hydroxide until it is molten in a solid state.

Dr.Bob - 2-8-2012 at 11:05

We wash glass in the base bath (NaOH in Ethanol/isopropanol/water mixture) often enough. If you leave a flask in there for more than overnight, you can start to notice that the tare weight will drop over time. I have seen flasks lose 10 mg in just one or two days of sitting in the base bath. So it would be hard to damage the flasks from thinning the glass unless you sat them there for weeks, but it could happen. But they do come out nice and clean.

MR AZIDE - 2-8-2012 at 15:33

Im sure I read somewhere a while ago that Caesium Hydroxide CsOH, if concentrated enough can dissolve glass.

I suppose finely ground sand, SiO2, may dissolve in hot / concentrated NaOH, producing sodium silicates.........havent tried it.

Magpie - 2-8-2012 at 15:53

My experiences:

Molten NaOH will frost a glass thermometer rather quickly.

Grinding some damp NaOH with mortar & pestle is a nice way to clean them up. :) Presumably a little of the ceramic is eaten away.