Sciencemadness Discussion Board

sodium borohydride analysis of activity

tritium - 23-3-2010 at 13:30

ladies and gentlemen,
I was wondering whether you are aware of an analytical technique that allows me to test a sample of sodium borohydride, NaBH4 for its activity (quality).
Though being manufactured and sealed in 2004, its lumps and should be a powder IIRC. A fellow chemist claimed it might have decomposed to NaBO2 and I would like to know before i buy.
Theres instrumental analytical equipment available to me but i cannot think of or find a method.
thanks in advance!

Lambda-Eyde - 23-3-2010 at 13:35

Decomposing it in aqueous solution and volumetrically measuring the hydrogen evolved is the standard method, IIRC.

Edit: I don't have any sources, but I have a strong recollection of reading that somewhere.
Can someone verify it by providing sources, or is someone perhaps disagreeing with me?

[Edited on 23-3-2010 by Lambda-Eyde]

arsen - 16-4-2010 at 20:07

You are right, volumetry is a typical procedure for alkali metal hydride, due to its simplicity and reasonable accuracy. That's usually how they assay hydrides.
Quote: Originally posted by Lambda-Eyde  
Decomposing it in aqueous solution and volumetrically measuring the hydrogen evolved is the standard method, IIRC.

Edit: I don't have any sources, but I have a strong recollection of reading that somewhere.
Can someone verify it by providing sources, or is someone perhaps disagreeing with me?

[Edited on 23-3-2010 by Lambda-Eyde]

mr.crow - 19-5-2010 at 16:35

Time to bring up an old-ish thread.

How about adding the NaBH4 to a stoichiometric amount of dilute HCl and using an analytical scale to measure the before and after. That way you know how much hydrogen escaped.

Would that work?

Magpie - 19-5-2010 at 18:40

Perhaps a redox titration as I show in my recent post on assaying sodium dithionite might work:

http://www.sciencemadness.org/talk/viewthread.php?tid=11785&...

mr.crow - 19-5-2010 at 19:25

I'm not sure how titration would work. The problem is it decomposes by itself in water and might reduce the indicator!

Measuring hydrogen volume sounds good. I'm not sure how I would assemble the apparatus so all the gas gets measured and not stuck in the tubes.

I would have to measure the mass accurately at the University anyways, so my method sounds like the easiest.