Sciencemadness Discussion Board

Separating KNO3 And NaN3

Kalium - 28-7-2012 at 04:52

I'm going to try and extract sodium azide from an airbag. Apparently they contain pellets made up of KNO3, NaN3 and SiO2. The SiO2 is easy to filter out due to its low solubility but I'm not sure how to handle the KNO3. Any ideas?

blogfast25 - 28-7-2012 at 05:13

Precipitate azide as lead azide with lead nitrate or lead acetate. Filter and wash.

Convert the lead azide back to sodium azide by treatment with Na2CO3: Pb(N3)2(s) + Na2CO3(aq) --- > PbCO3(s) +2 NaN3(aq). Lead carbonate is much less soluble than lead azide, so this displacement should proceed.

You're playing with detonator materials here. CAUTION!

[Edited on 28-7-2012 by blogfast25]

Kalium - 28-7-2012 at 05:29

Thanks for the reply.
Is it possible for the KNO3 to react with NaN3 to form KN3 when mixed in an aqueous solution? My chemistry skills have gone out the window lately...

Pok - 28-7-2012 at 05:36

In aqueous solution neither NaN3 nor KNO3 exist. You will have K+, Na+, N3- and NO3- ions. If you let it evaporate to dryness you may have a mix of every possible combination of these ions (NaNO3, KNO3, NaN3, KN3).

[Edited on 28-7-2012 by Pok]

Kalium - 28-7-2012 at 05:55

Ah, looking back I guess I worded it incorrectly. What I meant to ask was if KN3 would precipitate out, similar to how Pb(N3)2 or AgN3 would, but a quick look on Wikipedia revealed that it wouldn't.

blogfast25 - 28-7-2012 at 07:21

Fractionated crystallisation would be really difficult here because all species are well soluble. You'd lose substantial amounts of sodium azide. Rendering the azide insoluble is the only way I can see to recover it.

CaliusOptimus - 30-7-2012 at 18:35

I've extracted the sodium azide from a '97 mustang passenger airbag and the pellets inside don't seem to be contaminated with much, if anything. I was able to dissolve, filter, and evaporate the pellets leaving NaN3 that seems to be quite pure. All reactions I have done with it have given the expected yields for 98% reagents.

If it's an option, you'd be better off with a different airbag. (Mid 90's GM passenger side.) That is, assuming KNO3 will ruin your intended synthesis.

[Edited on 31-7-2012 by CaliusOptimus]

Kalium - 31-7-2012 at 04:29

It's great to hear that it worked for you. I've only heard of one other person attempting it. Is it very difficult to get inside the metal cylinder?
I live in Australia so a lot of available airbags come from Commodores and Falcons. I don't think they would have any fancy stabilisers or accelerants. Maybe I'll work on a passenger airbag from one of those.
The NaN3 is for AgN3; I'd only need a few grams so yields are not particularly important. As discussed above, the KNO3 shouldn't be a problem. Things are looking up for me! :)

CaliusOptimus - 31-7-2012 at 16:55

The inflator (aluminum cylinder with wire leads) was a tough piece of metal. I turned mine down on a lathe until the end cap came loose. In hindsight a band saw would have been my weapon of choice. But I know exactly where to cut now....

One airbag yielded about a pound of NaN3 :)