MrMario
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Reaction of NaBr and H2SO4
I wanted to prepare some Hydro bromic acid from Sodium Bromide and Sulphuric acid. Nurdrage prepares it by reacting Sodium Bromide solution with
Sodium bisulphate and an other users on YouTube do it by reacting Sodium Bromide with Sulphuric acid.
I searched on the web and the reaction formula seems to be:
NaBr + H2SO4 --> HBr + NaHSO4
So if sodium bisulphate is formed, then it could be used instu to form one more molecule of HBr right? Some salt participated on cooling and during
the reaction, is this Sodium bisulfate or Sodium Sulphate? I want to use the salt in a future experiment but want to be sure it is NaHSO4.
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Marvin
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That can work, but the conditions are a bit different and the way the gas coming off behaves would change with temperature. I've not made Hydrogen
Bromide this way but I've made Hydrogen Chloride and Nitric acid. With Nitric it's easier to aim for a Bisulphate product, sticking to lower
temperatures, less stress on the glassware and the bi product is molten when done and can be poured out. The neutral salt is rock hard and difficult
to dissolve off what was frequently (for me) a distorted Pyrex test tube. HCl is easier but there is more to it than just reagent cost. Having
reactions going smoothly is really helpful too.
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Metacelsus
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You'll want to make sure to avoid oxidizing your bromide:
2 HBr + H2SO4 → Br2 + SO2 + 2H2O
Therefore, don't use highly concentrated sulfuric acid, and avoid overheating during distillation (the azeotrope boils at 124 C, but you can lower
this by using reduced pressure).
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MrMario
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So best yields for Hydrobromic acid would be:
-Slow and cool addition of dilute H2SO4
-Distillation with reduced pressure
And would it be better to have Sodium Bromide in slight excess to make sure no Sulphuric acid is left when distilled?
My Hydrobromic acid was reduced in volume to increase concentration, but now has a slight orange tint and some dissolved salt precipitated (how do you
spell this word?) when cooled to RT. I guess that might be some dissolved bromine gas.
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Marvin
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HBr is a gas, it has an azeotrope with water at 50% (I think). Distilling it at low pressure might be bad plan, and boiling it may dilute it.
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UC235
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Use this procedure. It's cheap and effective. NaBr can be subbed for KBr if you adjust the mass appropriately.
www.sciencemadness.org/talk/files.php?pid=156645&aid=810...
I wouldn't bother trying to work up the waste. Fairly clean sodium bisulfate is extremely cheaply available as solid pool pH down. This procedure is
tolerant of moderately crappy sulfuric acid and any gunk in it will just need to be removed from the bisulfate.
[Edited on 6-2-2016 by UC235]
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MrMario
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Thanks! I wanted to use the sodium bisulfate in a dry distillation with sodium acetate to produce acetic acid, but i dont know if unpure product will
decrease the yield significantly.
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