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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: Vlad Soare on April 08, 2010, 04:28:59 AM

Title: NaOH in a Glass Bottle
Post by: Vlad Soare on April 08, 2010, 04:28:59 AM
Hello,

I've read that storing a solution of sodium hydroxide in a glass bottle is a no-no, because it reacts with glass to form silicon hydroxide.
Could someone please tell me what the actual reaction is?

Thank you.
Title: Re: NaOH in a Glass Bottle
Post by: Borek on April 08, 2010, 04:54:18 AM
More like sodium silicates. And it is usually not a serious problem (unless you are doing some highly specific work, where traces of Si contamination are detrimental to your results). But when storing NaOH in glass bottles you shouln't use glass stoppers, as they can get stuck.
Title: Re: NaOH in a Glass Bottle
Post by: Vlad Soare on April 08, 2010, 09:09:16 AM
Thanks, Borek. A slight silicon contamination wouldn't be detrimental; I'm only worried about the bottle. Laboratory glassware is expensive around here. Anyway, i have no problem with that; I'll just store it in a plastic bottle, and everything will be fine.
But I'd like to know what exactly happens, just for the sake of my curiosity. I'm trying to understand what reactions take place, and why.
Title: Re: NaOH in a Glass Bottle
Post by: Borek on April 08, 2010, 10:13:51 AM
Think about SiO2 as acid anhydride - it reacts with base just like CO2 does. Sure, it is not as eager to do so, but basic idea is the same.
Title: Re: NaOH in a Glass Bottle
Post by: BluRay on April 08, 2010, 10:14:45 AM
The essential information was the solution's concentration. An 1M solution don't give a lot of problems. A concentrated solution is another story.
Title: Re: NaOH in a Glass Bottle
Post by: Vlad Soare on April 08, 2010, 10:57:24 AM
The solution I'm using is around 100g per liter, so about 2.5M give or take.

Is the reaction something like this?
4NaOH + SiO2 :rarrow: Na4SiO4 + 2H2O

or maybe something like this?
4NaOH + SiO2 :rarrow: Si(OH)4 + 2Na2O

or maybe something completely different? ???
Title: Re: NaOH in a Glass Bottle
Post by: Schrödinger on April 08, 2010, 03:12:42 PM
Quote from: Vlad Soare on April 08, 2010, 10:57:24 AM
Is the reaction something like this?
4NaOH + SiO2 :rarrow: Na4SiO4 + 2H2O

or maybe something like this?
4NaOH + SiO2 :rarrow: Si(OH)4 + 2Na2O
The second one doesn't look alright. The first one is a typical acid base reaction...you're thinking on the right lines.
As Borek pointed out, since Si is in the same group as C, SiO2 should be expected react like CO2. So, Na2SiO3 would seem alright, but I'm not very sure.
Title: Re: NaOH in a Glass Bottle
Post by: Vlad Soare on April 09, 2010, 02:30:28 AM
I see. Thank you.
Title: Re: NaOH in a Glass Bottle
Post by: Vlad Soare on April 16, 2010, 07:15:34 AM
I think I understand now. I believe the reaction is:
2NaOH + SiO2 :rarrow: Na2SiO3 + H2O

But now I have another question. :)
It seems to me that silicon dioxide actually reacts with hydroxide ions, and not with NaOH per se (I mean, sodium ions don't participate in the reaction). The actual reaction seems to be like this:
Na+ + 2(OH)- + SiO2 :rarrow: Na+ + (SiO3)- + H2O

This means that silicon dioxide should theoretically react with any strongly basic solution. Is this correct? Does it react with other strong bases, like Na2S for instance? I have a 1% solution of sodium sulfide (approximately 0.13M), and it's extremely basic (my paper test strips show pH 14, though I believe it's probably a little lower than that in reality). Will it attack glass, too?
Title: Re: NaOH in a Glass Bottle
Post by: Borek on April 16, 2010, 08:14:23 AM
Quote from: Vlad Soare on April 16, 2010, 07:15:34 AM
Na+ + 2(OH)- + SiO2 :rarrow: Na+ + (SiO3)- + H2O

Go net ionic:

SiO2 + 2OH- -> SiO32- + H2O

Quote
This means that silicon dioxide should theoretically react with any strongly basic solution. Is this correct? Does it react with other strong bases, like Na2S for instance? I have a 1% solution of sodium sulfide (approximately 0.13M), and it's extremely basic (my paper test strips show pH 14, though I believe it's probably a little lower than that in reality). Will it attack glass, too?

Your thinking is correct and it would be not surprising. But it is chemistry, so it can always happen that logical ideas are in fact completely irrelevant ;)
Title: Re: NaOH in a Glass Bottle
Post by: nj_bartel on April 16, 2010, 07:21:25 PM
That pH doesn't seem possible to me with a concentration of .13 and a base that can only pick up 2 protons (reasonably).
Title: Re: NaOH in a Glass Bottle
Post by: Borek on April 17, 2010, 04:04:34 AM
Around 12 wouldn't be surprising and universal papers are far from being precise enough at the ends of the scale. Could be they don't like presence of concentrated sulfides.
Title: Re: NaOH in a Glass Bottle
Post by: Vlad Soare on April 19, 2010, 02:47:20 AM
Yup. I know it can't be 14 at that concentration, but unfortunately those cheap paper test strips are all I have at hand for measuring pH at this time. :-[

Quote
But it is chemistry, so it can always happen that logical ideas are in fact completely irrelevant
Good point. :)
So, in this particular case, are they? OK, maybe sodium sulfide wasn't the best example, but are there other strong bases that can attack glass?
Title: Re: NaOH in a Glass Bottle
Post by: Borek on April 19, 2010, 03:46:01 AM
Anything with high pH will attack glass IMHO.