Sciencemadness Discussion Board

Isolation of argon

Titi - 26-6-2025 at 11:43

Good evening everyone,

I wish to recreate the experiment of chemical argon isolation. Two methods were used.

-The first consists of an electric discharge in a closed container of air with a base at the bottom. Nitrogen reacts with oxygen forming nitric oxydes, which reacts with the base, removing nitrogen from the air.
It is clearly necessary to add oxygen so that all nitrogen can react. Still, I guess that when nitrogen becomes rare, the reaction happens slower and slower, and so it may be hard to remove enough nitrogen to have a reasonnably pure argon.
And anyway, it is necessary after to remove the oxygen.

-The second consists of reacting oxygen and nitrogen chemically to bind them. A description of the experiment is avalaible here
https://www.chem.ucl.ac.uk/resources/history/chemhistucl/his...
Oxygen is reacted with red hot copper, nitrogen by hot magnesium, and water vapor by phosphorus pentoxide. So that only argon stays.

So now neither methods seem very practical for the amateur chemist. I don't have a machine to make sparks, and I think that removal of nitrogen will not be complete enough, and so chemical reaction will be necessary anyway. So I think the second approach may be simpler, and unavoidable anyway.

Still, I would prefer to avoid the red hot copper and magnesium. I know that lithium reacts with nitrogen at much lower temperature. But would it react readily in solid form? As liquid lithium reacts with glass, I can't heat it. Could we mix it with another metal, so that melting point stays low, but it becomes less reactive with glass? Is lithium enough to react with all the oxygen and nitrogen, or should we use also another metal?

Also, the amount of metal needed could be problematic. To make 1L of argon, we need around 100L of air, so 4 mol of gas. For nitrogen, we need 6 times more, and oxygen 4 times more, so around 22 mol, so let us say 150g.

The setup I imagine is to circulate air with a pump though a dessicator filled with lithium, and let air enter periodically to compensate the loss of air volume.

A last approach, a little cheating, is to use oxygen concentrators. As I unterstand, they selectively remove nitrogen, but not argon. This would remove most of the nitrogen, and removing the oxygen part could avoid lithium.

Finally, I have a curiosity question: Is it possible to further separate the noble gases without fractional distillation? I know that PtF6 readily reacts with xenon, but even forgetting the impracticality of this reaction, would it work when xenon concentration is less than 1 part per 10^5? What are other possible ways?

bnull - 26-6-2025 at 12:44

Solid lithium reacts with nitrogen, oxygen, and water vapor. I lost a perfect sample of lithium this way.

Rayleigh and Ramsay's method is simple. Not practical for isolation of liters of argon but, if you just want to replicate the experiment, that should do. You have the advantage of power supplies and more than a century of chemistry.
Quote:
So now neither methods seem very practical for the amateur chemist.

High voltage circuits are a dime a dozen. High voltage transformers, like those used in mosquito zappers (1 to 5 kV, been zapped in the finger once), are somewhat easy to find. Same with old TV flyback transformers.

j_sum1 - 26-6-2025 at 14:10

OTOH, if you are just after some argon
  • welders' suppliers
  • wine shops – sell (overpriced) cans of high purity argon to insert into the top of opened bottles of wine to prevent further oxidation. A bit of a gimmick for wine snobs, but the idea is there.


    An extra problem that you have not mentioned is determining if your have the product you want. At the end of the day, how will you test that the gas you have collected is (predominantly) argon?

    RU_KLO - 27-6-2025 at 04:23

    "An extra problem that you have not mentioned is determining if your have the product you want. At the end of the day, how will you test that the gas you have collected is (predominantly) argon?"

    Could this be tested by weight?

    Or inserting a reagent (or lithium) that is very reactive (in O2, N2, etc) in that atmosphere?

    Titi - 27-6-2025 at 13:09

    The weight could be a method. 1L of argon should weight around 400 mg more than the empty flask (filled with air). A scale with such precision is easy to find. I did not know about argon for wine, thank you, this can be useful, as this is pratical for very small quantities.

    If argon is isolated with lithium, then nothing else than argon (and other noble gases) can stay. But more problematic would be leaks, which would insert air, and so the lithium would continue to react until exhauted.

    For the spark method, I'm curious about how much power is necessary. This requires high voltage, and I don't want to touch any microwave transformer.

    chempyre235 - 27-6-2025 at 20:53

    Quote: Originally posted by Titi  
    Finally, I have a curiosity question: Is it possible to further separate the noble gases without fractional distillation? I know that PtF6 readily reacts with xenon, but even forgetting the impracticality of this reaction, would it work when xenon concentration is less than 1 part per 10^5? What are other possible ways?

    Maybe some kind of mass spectrometry setup? This is the only way I could think of that doesn't use fractional distillation. If PtF6 is able to react with xenon, chances are it would react with oxygen, nitrogen, water and carbon dioxide first. If you're just looking for xenon, you might be able to get ahold of some xenon bulbs.

    Fulmen - 28-6-2025 at 01:02

    You don't need much power to generate sparks. I agree that MOTs are a bit on the dangerous side, try this instead:
    https://www.aliexpress.com/item/1005006803334147.html

    As for identification, argon has visible spectral lines. If you already have a high voltage transformer a bit of vacuum shouldn't be too hard.

    Radiums Lab - 28-6-2025 at 08:29

    I don't think isolation of argon using lithium metal is a feasible option or a good one.
    Rather buy an argon tank instead of using precious Li metal.

    bnull - 28-6-2025 at 13:23

    Quote:
    Rather buy an argon tank instead of using precious Li metal.

    That defeats the main purpose of the OP, which is
    Quote: Originally posted by Titi  
    to recreate the experiment of chemical argon isolation.

    Identification of argon in a gaseous sample can be done by its emission spectrum. The sample doesn't need to be large; a few tenths of mL should do (let's say 0.5 mL) since this can be done at low pressure. Air is roughly 1 percent argon, so one needs to remove 49.5 mL of nitrogen and oxygen and what-not from 50 mL of air. Using lithium as scrubber, one would need 100 mg of lithium (an excess, if my numbers are right), which is about the amount in a fresh CR2032 cell. Not really expensive if isolation and identification is the purpose. There only remains the spectrometer, DIY projects of which abound in the Web.

    A simple solution (as far as my glassblowing abilities go) is to seal a couple of electrodes a distance apart in a glass tube, put a piece of lithium inside it and seal the open end of the tube. If the seals are good, after a while there will be argon and a very small amount of anything else there.

    [Edited on 28-6-2025 by bnull]

    AdamAlden - 28-6-2025 at 21:10

    what the hell ? im confused argon i couldnt real with all the fluff so im just gunna ask and dont ask me what fluff is plz... what r u extracting argon from?

    bnull - 29-6-2025 at 03:28

    Quote: Originally posted by AdamAlden  
    what the hell ? im confused argon i couldnt real with all the fluff so im just gunna ask and dont ask me what fluff is plz... what r u extracting argon from?

    Well,
    Quote: Originally posted by bnull  
    Air is roughly 1 percent argon