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Author: Subject: Weak Hydroxide solutions Eating Glassware?
MichiganMadScientist
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shocked.gif posted on 29-9-2013 at 09:51
Weak Hydroxide solutions Eating Glassware?


Hi There:

We all know that strong concentrations of hydroxide will eat through glassware. Especially if one applies heat.

My question is: I have frequently prepared relatively weak solutions of hydroxides (perhaps < 3.0-5.0 Molar) in volumetric glassware. I'm usually pretty decent in terms of washing out my glassware when I'm done, but suppose I only used water to wash out these flasks, and then left them to dry in my store room for several months.

Can I reasonably expect degradation of my glassware from residual hydroxides that may have not perfectly washed away? What is your experience with weak Hydroxide solutions degrading glassware? Or is it safe to assume that only strongish solutions of Hydroxides put glassware at appreciable risk?

Thanks for your help.:)

[Edited on 29-9-2013 by MichiganMadScientist]
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Chemosynthesis
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[*] posted on 29-9-2013 at 10:18


Should be fine. I generally have not found appreciable degradation of glassware from base baths used in cleaning if washed within the day.
I would be a little more careful with calibrated analytical glassware, even if out of paranoia. If you're worried, wash with a weak acid. That's similar in concept to how we cleaned fritted funnels that were base sensitive (nitric bath).
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sonogashira
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[*] posted on 30-9-2013 at 01:30


Quote: Originally posted by MichiganMadScientist  
We all know that strong concentrations of hydroxide will eat through glassware.


What? No one told my 50% NaOH! :P
Where have you heard this?! Slight etching perhaps, but not eating through glassware, surely? :o
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MichiganMadScientist
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[*] posted on 30-9-2013 at 01:41


So, it's safe to say that any residual NaOH left behind from weak solutions will have no long term effect on my glassware? You're making it sound like even strong solutions only have a negligable effect?
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sonogashira
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[*] posted on 30-9-2013 at 01:50


I don't know where you have come across this information. I have stored 50% aqueous NaOH solution in a glass bottle for several years, Perhaps you have confused it with molten sodium hydroxide?
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[*] posted on 30-9-2013 at 01:51


I've seen strong NaOH etch a noticeable step in a glass jar (soda lime type), if I had to guess, maybe 5 thousandths of an inch (about 0.12mm). It sat for some time at room temperature, maybe weeks. It wasn't frosted, but remained polished.

Weak solutions should fairly quickly absorb sufficient CO2 from the atmosphere to drop the pH out of the danger zone as they dry. Probably the pH of tap water is comparable, after rinsing, anyway (which can be 8-9 with hard, alkaline water, I think?). A squirt of white vinegar would be cheap insurance, but probably unnecessary.

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woelen
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[*] posted on 30-9-2013 at 03:20


Strong solutions do have effect on glassware, but only very slowly. I once allowed a concentrated solution of NaOH stand in a jar for a few weeks. After that, the jar was a little bit frosty from the bottom, up to the level of the surface of the liquid.

A weak solution will take an even longer time to etch your glass, but I would suggest to rinse your glassware quite well if you put it away for weeks. You do not have to fear serious damage if you keep it wet with a weakly alkaline solution for a day or so.

When I clean my glassware for long-term storage, I rinse with tapwater, then with a little amount of dilute acetic acid (3% or so) and then with distilled water and then I put away the glassware, unstoppered. Then, after months of storage, the glassware is perfectly clean and I can use it right away out of the box. Acetic acid is very nice for this, because if small residues of this acid remain, then these simply evaporate and no non-volatile residue remains behind. I use real acetic acid and not household vinegar. The latter may have salts, spices and sugars as non-volatile residue.




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[*] posted on 30-9-2013 at 07:14


It surely won't eat through the glass, but it will affect first class precision calibrated volumetric glassware if the exposure is often and it lasts for a long time or the temperatures are higher than specified. I wouldn't tease my expensive stuff like that.

If you need to expose such glassware to mild alkalis, do it fast and later use a quick HCl soak.




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[*] posted on 30-9-2013 at 07:18


Let's not forget about how NaOH solutions can cause ground glass stoppers and connections to stick after lengthy exposure, had it happen once and I ruined the neck of the bottle trying to remove it.
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[*] posted on 30-9-2013 at 07:54


Exactly why I prefer hollow stoppers. If all else fails, break off the head of the stopper, then shatter the inside of the stopper with a hammer and nail. Stoppers are relatively cheap, and this saves the bottle (+ contents).



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[*] posted on 30-9-2013 at 09:31


Well, now I'm paranoid. In reality, I always wash my stuff before storage, but I haven't made a habit of doing acetic acid washes. Right now, my glassware has gone over a year without obvious etching, but I'm scared too see how it will look in five years. Additionally, most of my volumetric stuff was purchased used, and all bears minor scratches. Maybe I'll try and save up to buy all new volumetric flasks....
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[*] posted on 30-9-2013 at 11:05


Quote: Originally posted by woelen  
When I clean my glassware for long-term storage, I rinse with tapwater, then with a little amount of dilute acetic acid (3% or so) and then with distilled water and then I put away the glassware, unstoppered. Then, after months of storage, the glassware is perfectly clean and I can use it right away out of the box. Acetic acid is very nice for this, because if small residues of this acid remain, then these simply evaporate and no non-volatile residue remains behind. I use real acetic acid and not household vinegar. The latter may have salts, spices and sugars as non-volatile residue.
I just use a wash of the hottest tap water I can manage (usually badly scalding my hands) followed by thorough rinsing with distilled water, thrice. Finally, I dry it in a dust-free environment or an oven, and cover openings with Al-foil before storage. It's clean enough for amateur analytical work right out of storage.



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[*] posted on 1-10-2013 at 18:31


I think the answer to your question is dependent on the purpose of the glassware you are talking about. When I perform any analytical work I always use a dilute nitric acid bath followed by a good three washings with DI water. I like to squeeze as much performance out of my equipment as possible. I didn't spend money on my class A stuff for nothing.

As for your concerns of residual NaOH on your analytical glass, everyone is probably correct. Its fine. However I would be worried about the effects that residual NaOH will have on the next solution I prepare in the volumetric flask.
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sonogashira
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[*] posted on 2-10-2013 at 05:03


Perhaps you should do a simple acid base titration to see how much "residual NaOH" you have left after washing your glassware thoroughly with water. You will find none.
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