JefferyH
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Sodium Borohydride identification/verification?
I'm getting a smallish quantity of sodium borohydride from China, all customs duties taken care of, etc.
I of course want to verify compound and the purity. I was taking a look at the other borohydride thread in this board, and liked the idea about the
hydrogen gas being generated.
I'm thinking I could just drop a known quantity of borohydride into a sealed container with a pressure-gauge, and calculate the H2 based on how much
pressure builds up. Seems like I could build something out of PVC very easily.
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UnintentionalChaos
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That seems really excessive compared to just blowing the gas from a flask into an inverted graduated cylinder full of water and reading the volume.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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FireLion3
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How exactly do I get the gas into the inverted cylinder? Your description is a little confusing and hard to picture.
[Edited on 18-6-2014 by FireLion3]
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UnintentionalChaos
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Quote: Originally posted by FireLion3  |
How exactly do I get the gas into the inverted cylinder? Your description is a little confusing and hard to picture. |
Take a large graduated cylinder, fill it with water, and carefully invert into a shallow dish of water. As long as you don't allow air bubbles into
the cylinder, it will remain filled. I suggest using a lab clamp to hold the cylinder in place. Now, use a flask with a gas offtake adapter and some
tubing to combine the borohydride with water and lead the produced gas under the bottom edge of the graduated cylinder. It will displace water into
the dish below it, and the volume of gas produced can be read off the normal markings on the cylinder.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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FireLion3
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| Quote: Originally posted by UnintentionalChaos | | Quote: Originally posted by FireLion3 |
How exactly do I get the gas into the inverted cylinder? Your description is a little confusing and hard to picture. |
Take a large graduated cylinder, fill it with water, and carefully invert into a shallow dish of water. As long as you don't allow air bubbles into
the cylinder, it will remain filled. I suggest using a lab clamp to hold the cylinder in place. Now, use a flask with a gas offtake adapter and some
tubing to combine the borohydride with water and lead the produced gas under the bottom edge of the graduated cylinder. It will displace water into
the dish below it, and the volume of gas produced can be read off the normal markings on the cylinder. |
Won't some gas inevitably escape in this technique? JefferyH's idea doesn't sound too complicated in comparison to what you have described. Perhaps it
is because I have never really seen this done before how you described it.
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JefferyH
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I see what you're saying, UnintentionalChaos. I'm lacking a bunch of glassware to pull that off. I may look into it.
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forgottenpassword
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Why do you have reason to doubt it's identity?
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woelen
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An even simpler methoid is to measure a small amount of NaBH4 (e.g. 100 mg) and put that in a large syringe, while still dry. Next, suck in 10 ml or
so of dilute HCl (5% or so) and quickly seal the tip of the syringe with your finger. The plunger will move outwards as the hydrogen gas is produced.
If so much gas is produced that the plunger will go beyond the end of the syringe, then release some of the gas under water, in an inverted bottle,
otherwise just let it go.
After this, you can measure the amount of gas produced and estimate the fraction from what you would expect from 100 mg of pure NaBH4. This process is
not really accurate, but it certainly can be done at 10% accuracy, enough to get some idea of the remaining effectiveness of the NaBH4.
NaBH4 can become less effective when badly stored. I once purchased 25 grams of this chemical from a somewhat shady seller and when I received the
material, I found out that most of it was converted to sodium borate and only a small fraction of its reducing power was left.
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JefferyH
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What do you consider badly stored? Typical transport is in sealed aluminum bags. Shouldn't most any relatively airtight container do the trick?
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