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Author: Subject: Analysis of N2O
1281371269
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[*] posted on 30-1-2011 at 08:16


I've done some further tests and am pretty much stumped.

I passed the gas (x) through a heated glass tube as before, then the exhaust gasses (y) were bubbled through distilled water to form a solution (n). Any gases (z) that didn't dissolve in water were passed through another length of tubing and bubbled through Bromine water.

The exhaust gasses (y) didn't seem particularly soluble - after a short while I noted dense white fumes sitting above the solution (n) in the gas washing bottle and also coming out of the last length of tubing as z. I remember seeing similar looking fumes when we cracked longer chain hydrocarbons in school last year, so they would seem to fit with the HX + alkene idea. However, they were still turning indicator paper dark red and didn't seem to decolourise Br2 water (though I would need to repeat this test to be sure)

The solution (n) didn't give a product with the silver nitrate halide test. It was also only slightly acidic (pH ~3-4). Both of these again match the HF idea. However, n also doesn't seem to give a precipitate when mixed with warm CaCl2 solution. Do I need to heat it? How difficult is it to see the precipitate?

I don't really know what other tests to do or what conclusions to draw from this...

Thanks again for the help,

Mossy.
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[*] posted on 30-1-2011 at 08:53


Also, I've double checked and he would still like to pass the stuff on to a proper lab for further testing. Does anyone here (around London, UK) have the machinery to carry out that kind of analysis (for a reasonable sum) or know of somewhere which would do it?
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[*] posted on 30-1-2011 at 08:59


Don't listen to Ozone, hes only trying to ripe you off and make a quick buck...... Ill only charge you $75

Lol!

The green/blue flame color is the tell. I agree with GC, as he beat me to it (I though the same thing when you mentioned the green flame test). Excellent testing, by the way; it's amazing how many forget about flame tests, these days.

Also, if the collar on the bunsen is copper (or copper alloy), the resulting HCl can give CuCl2 which is volatile and gives a nice green flame color; this is the basis of a reliable test for organic halogen--flame test on copper.

Cheers,
O3




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[*] posted on 30-1-2011 at 10:05


Yes, definitely flame tests can tell a lot but are not used much these days...

There used to be a copper test, where the tip of a copper wire was allowed to stand in a flame until it no longer colored it (covered by non-volitile oxide). Then the passivated wire was dipped into the halocarbon so the tip was moistened. Finally the tip was put back into the flame, Cl, I and Br would give distinct flame colors as they all yield volatile copper salts, however Fluorocarbons do not color the flame because there copper salts are non-volatile. I don't know exactly how this can be modified to work on a gas but I am sure something could be worked out.

It also might be a good idea, to do a gas density test. This could help immediately rule out N2O.

Based on what you have indicated, I think it is highly likely that you are dealing with a fluorocarbon, probably either di, tri, or tetrafluoroethane.

Also, inhaling the stuff will probably tell you little; all anesthetics make people a little silly. This includes, fluoroalkanes, choloroalkanes and N2O.

[Edited on 1-30-2011 by smuv]
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[*] posted on 1-2-2011 at 10:59


I'll definitely try that copper wire test, thanks.

I also had another idea about testing for HF: I measure the pH of the solution (I can only do this roughly, with UI indicator paper) before addition of CaCl2, and then again afterwards. If HCl has been formed, I should see a notable increase in pH - not only because HCl is a better acid, but because two moles are formed for every mole of HF.
However, CaCl2 is basic in solution - will this significantly affect my pH values?
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[*] posted on 9-2-2011 at 12:39


I've pretty much found out all I can with they equipment available to me - and I've been paid (not £100, £40, but I'll get more if I can find out precise details).

Does anybody know of somewhere in the UK which will run the gas through a mass spec for me? (I think that should be enough, but if it's inconclusive then I guess GC / NMR). How much is it likely to cost?
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