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Topic: NaBr + H2SO4 = ?  (Read 73124 times)

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Offline painkiller

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NaBr + H2SO4 = ?
« on: July 03, 2007, 12:39:41 PM »
Hi !

I have trouble figuring out the products of this reaction
NaBr + H2SO4 =

I know that Br- will reduse H2SO4 to SO2 but what about Na+ ions ?
Will it form a Na2SO4 ?

Thanks in advance


Offline AWK

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Re: NaBr + H2SO4 = ?
« Reply #1 on: July 04, 2007, 01:16:04 AM »
This reaction takes place with over 70 % H2SO4
NaBr + H2SO4 = Na2SO4 + Br2 + H2O + SO2

Balance this reaction
AWK

Offline painkiller

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Re: NaBr + H2SO4 = ?
« Reply #2 on: July 04, 2007, 06:05:46 AM »
Thank you ! you are my savior  ;D

Offline woelen

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Re: NaBr + H2SO4 = ?
« Reply #3 on: July 12, 2007, 03:07:30 AM »
The reaction, posted by AWK indeed takes place, but I would not say that Na2SO4 is formed, but NaHSO4 (but that only is a minor detail).

More important, there also is another reaction and the majority of all bromide will end up with this:

H2SO4 + NaBr --> NaHSO4 + HBr

The reaction, mentioned by AWK is a side-reaction. So, in practice, when you add concentrated H2SO4 to NaBr, then HBr will be formed, which is contaminated with SO2 and Br2.

With NaCl instead of NaBr, only HCl is formed, the free halogen is not formed in that reaction.

With NaI instead of NaBr, the majority of the material is oxidized to iodine, SO2 and even H2S being formed from the acid. With NaI, only a small part of the iodide is converted to HI when concentrated sulphuric acid is added.
Want to wonder? See http://www.oelen.net/science

Offline AWK

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Re: NaBr + H2SO4 = ?
« Reply #4 on: July 12, 2007, 06:05:43 AM »
Yoa are right (at room temperature) and not right (at elevated temperatures)
Usually the temperatute is enough to remove bromine from reaction mixture bt distillation (over 60 C), and then my reaction is correct.
AWK

Offline woelen

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Re: NaBr + H2SO4 = ?
« Reply #5 on: July 12, 2007, 05:38:21 PM »
Your reaction is always correct, but there also always is another reaction. Both reactions occur at the same time. I can imagine that the higher the temperature, the more your reaction will occur, but I do not know of any situation, where only your reaction occurs, nor do I know of a situation, where only my reaction occurs.

This is a bad thing, because it makes this kind of reactions totally useless for preparative purposes. HBr cannot be made in a satisfactory way with this reaction, nor bromine.
Want to wonder? See http://www.oelen.net/science

Offline AWK

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Re: NaBr + H2SO4 = ?
« Reply #6 on: July 13, 2007, 12:47:11 AM »
This is a first step of my redox reaction.
2NaBr + 3H2SO4 = 2NaHSO4 + Br2 + 2H2O + SO2

The next step is:
2NaBr + 2NaHSO4  + H2SO4 = 2Na2SO4 + Br2 + 2H2O + SO2

When bromine is removed from reaction mixture (over boiling point of bromine) this reaction comes to completion (sum of both reactions)
4NaBr + 4H2SO4 = 2Na2SO4 + 2Br2 + 4H2O + 2SO2
and finally
2NaBr + 2H2SO4 = Na2SO4 + Br2 + 2H2O + SO2
AWK

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