Sciencemadness Discussion Board

Melting NaOH in a glass tube

teodor - 18-7-2019 at 04:58

I tried to analyze some unknown substance with a melting point close to that of NaOH. So, I did a reference test to compare how NaOH melts. I've got a Pasteur pipette, sealed one end and put a tiny amount of OTC grade NaOH inside. On melting it becomes instantly boiling (that was I thought when I saw it). I did the check that my NaOH is not a hydrate (by titration with HCl), it isn't. So, I think this "boiling" is a violent reaction of molten NaOH with glass. Not surprised, but what exactly this reaction is and what is the gas which bubbles?

[Edited on 18-7-2019 by teodor]

fusso - 18-7-2019 at 05:31

2NaOH+SiO2=Na2SiO3+H2O
Na2SiO3+2NaOH=Na4SiO4+H2O(?)
Na2SiO3+xSiO2=Na2O*(x+1)SiO2
So the gas maybe water vapour?

teodor - 19-7-2019 at 03:00

Oh, thank you, fusso. So, I believe it is the same reaction as between NaOH water solution and glass. And SiO2 acts like an acid.

Actually I was surprised by the reaction dynamic. I didn't expect that this reaction is so violent when NaOH is molten. Now I can use this simple test as a check for hydroxide.

morganbw - 19-7-2019 at 06:26

Quote: Originally posted by teodor  
Oh, thank you, fusso. So, I believe it is the same reaction as between NaOH water solution and glass. And SiO2 acts like an acid.

Actually I was surprised by the reaction dynamic. I didn't expect that this reaction is so violent when NaOH is molten. Now I can use this simple test as a check for hydroxide.


I would google on how to test for hydroxides. I do not think this is a test you want to add to your bag of tricks.
Lots of info on this.

teodor - 20-7-2019 at 03:02

Quote: Originally posted by morganbw  
I do not think this is a test you want to add to your bag of tricks.


Well, this test, also, probably, will distinguish between NaOH and Na2O2, Na2O.