kazaa81 - 11-9-2005 at 14:25
Hallo to all,
I was making some boric acid (H3BO3) from sodium perborate, by adding conc. H2SO4 to this last.
A foamy white mass has produced. The beaker in which this foam has formed has been warmed over a flame, dissolving some of the product on the bottom
and foaming a little more.
However i think the heat was not sufficient to produce glassy boric oxide, because nothing solid has formed.
I've put a little of this foam in some denaturated ethyl alcohol, bought in any store, which is dyed pink. Almost immediately color pink became
colorless.
What's happened? Also, how can i get boric oxide (glassy) from the boric acid i prepared?
Any information/experience welcomed!
12AX7 - 11-9-2005 at 19:08
What a waste of perfectly good high-oxidation state chemical. 
It decolorized it because it bleached the color out.
To melt boric acid you need a red heat.
Tim
Cyrus - 12-9-2005 at 09:26
I would suggest that you use borax (Na2B4O7) and hydrochloric acid and heat them up (I forget exactly how much). On cooling, a large amount of boric
acid crystals will precipitate. After washing and drying them, heat them in a crucible over a flame, and then you'll get some boron oxide. To
read more about my mishaps using this method, go to the thread "silicon (and boron)"
[Edited on 12-9-2005 by Cyrus]
Mumbles - 12-9-2005 at 11:28
The ratio is 46.3g Sodium borate dissolved in the smallest amount of water(~85mL) to 20.3mL HCl. I don't know if that ratio is dried or not.
I assume not as the proceedure references "borax" which is generally used to describe the material straight from the box. Cooling that
mixture will result in boric acid precipitating.
kazaa81 - 12-9-2005 at 12:15
Thanks at all very much!
12AX7, it wasn't a waste, there was just 1 ml of ethanol, denaturated of course!
Why is preferable obtaining H3BO4 from HCl than from H2SO4? Because of the foam formed?
I will try to get B2O3 (boric oxide) from boric acid in a hot crucible....
I've tried to obtain B2O3 by heating foamy H3BO3 in a beaker, but while melting some on the bottom, a nice "crack" has formed on the
beaker....
Also, for a chemist, "bleaching out" isn't a thing of his language, more explanation would be appreciated....(ethyl borate?)
Any information welcomed!
Mumbles - 12-9-2005 at 12:50
The colorant was oxidised by the perborate ion. I don't know the colorant so I can't tell you if any intermediates were formed, but
complete oxidation would form CO2 and H2O. There is so little colorant you'd never notice the CO2.
As for the H2SO4 vs. HCl. I imagine the cost has something to do with it. Dilution of the sulfuric acid may also be needed. I have always assumed
the water plays a roll in the reaction.
Na2B4O7 ---> B2O3 + Na2O
B2O3 + Na2O + 4 H2O ---> 2 NaOH + 2 B(OH)3
That is how I assume the reaction proceeds. It may not actually follow those steps, but thinking about it like that makes it a bit more logical I
believe.
[Edited on 9-12-2005 by Mumbles]
[Edited on 9-12-2005 by Mumbles]
kazaa81 - 13-9-2005 at 14:13
How would ethyl borate forms? Any nice boric acid salt? B2O3 glass?
Any information welcomed!
Reverend Necroticus Rex - 13-9-2005 at 18:40
Funny enough, I have also noticed that just a prill or two of anhydrous NaOH decolorise a bottle of that purple-dyed denat. EtOH, when shaken for a
while, without visually appearing changed.
FrankRizzo - 16-9-2005 at 19:53
Kazaa81,
You may already know this, but most hardware/home improvement stores in the US have large bottles of pure boric acid sold cheaply for use as an
insecticide. My local store has a 3lb bottle for $2.79.
kazaa81 - 19-9-2005 at 12:41
Thank you Frank,
but I don't have access to US suppliers, I'm a little away from US now.