[Vlad Soare]

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.

[Borek]

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.

[Vlad Soare]

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.

[Borek]

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.

[BluRay]

The essential information was the solution's concentration. An 1M solution don't give a lot of problems. A concentrated solution is another story.

[Vlad Soare]

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 Na₄SiO₄ + 2H₂O

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

or maybe something completely different?

[Schrödinger]

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

or maybe something like this?
4NaOH + SiO₂ 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.

[Vlad Soare]

I see. Thank you.

[Vlad Soare]

I think I understand now. I believe the reaction is:
2NaOH + SiO₂ 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 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?

[Borek]

Na⁺ + 2(OH)^- + SiO₂ Na⁺ + (SiO₃)^- + H₂O

Go net ionic:

SiO₂ + 2OH^- -> SiO₃^2- + 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?

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

[nj_bartel]

That pH doesn't seem possible to me with a concentration of .13 and a base that can only pick up 2 protons (reasonably).

[Borek]

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.

[Vlad Soare]

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.

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?

[Borek]

Anything with high pH will attack glass IMHO.