DoctorOfPhilosophy
Hazard to Others
Posts: 130
Registered: 12-6-2012
Location: Ontario, Canada
Member Is Offline
Mood: enthralled
|
|
Sodium hydroxide versus glass
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
Hazard to Others
Posts: 380
Registered: 16-4-2012
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Others
Posts: 175
Registered: 20-5-2011
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 3253
Registered: 13-7-2003
Location: Wisconsin
Member Is Offline
Mood: Rock n' Roll
|
|
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
International Hazard
Posts: 1468
Registered: 17-7-2011
Location: shores of a solar sea
Member Is Offline
Mood: speeding through time at the rate of 1 second per second
|
|
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
National Hazard
Posts: 860
Registered: 20-11-2008
Location: Norway
Member Is Offline
Mood: Cleaved
|
|
Storing NaOH solutions in glass is perfectly safe as long as it doesn't have a ground glass stopper. It will easily jam those.
This just in: 95,5 % of the world population lives outside the USA
Please drop by our IRC channel: #sciencemadness @ irc.efnet.org
|
|
|
polymerizer87
Harmless
Posts: 35
Registered: 16-7-2012
Member Is Offline
Mood: No Mood
|
|
I've found it will etch the glass overtime, but nothing more than what conc. acids will do.
|
|
|
simba
Hazard to Others
Posts: 175
Registered: 20-5-2011
Member Is Offline
Mood: No Mood
|
|
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 |
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
Harmless
Posts: 4
Registered: 26-7-2012
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 2750
Registered: 26-1-2011
Location: USA - NC
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Self
Posts: 64
Registered: 21-5-2012
Location: UNITED KINGDOM
Member Is Offline
Mood: Fizzing
|
|
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
lab constructor
Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline
Mood: Chemistry: the subtle science.
|
|
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.
The single most important condition for a successful synthesis is good mixing - Nicodem
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
