metalresearcher
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Why is isolating Na more difficult than isolating K ?
Several times I have isolated potassium metal using KON + Mg. I put it in a 316 stainless steel retort with a screwed lid which is welded to a steel
pipe leading into a jar with mineral oil. I used Teflon tape as a (single use) seal in the thread. Then I heat it strongly with a propane flame. It
does work despite the temperature is well above the teflon rating, hence its single use. checked temperature with an infrared pyrometer which read
1100 C on the outside of the retort, well above the boiling point of Na (883 C).
But whe I do the same wit NaOH + Mg, barely Na metal is formed. Only in the retort tube. After the reaction is finished and the retort is cooled down,
I open it and carefully (gloves + face shield !) I pour some water into it it reacts explosively with bright yellow flames. But no Na metal in the
oil, unlike K.
When I do the same with KOH + Mg, the result is some small 5-10mm diameter balls of K metal.
Why is sodium more difficult than potassium ?
[Edited on 2025-9-28 by metalresearcher]
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Chemgineer
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Have you looked into this video by Nurdrage https://www.youtube.com/watch?v=BsNoiFj3wlw
I've done this a couple of times and it worked very well, just a bit tricky to get the sodium out of the flask at the end.
I used some starting sodium in the reaction to start with as described but I ended up with tripple the quantity at the end.
[Edited on 28-9-2025 by Chemgineer]
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teodor
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Do you use excess of Mg in both cases? Because the yield could be dependent on free water, both KOH and NaOH adsorbs it but it could be the case that
the different amount is present. As for NaOH it even could be in the form of NaOH * H2O. For both cases I think it is better to melt it and heat until
all water will evaporate.
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Deathunter88
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It appears that over a wide temperature range the vapor pressure of Na is about one or two orders of magnitude lower than that of K, which would
correspond to probably a similar magnitude difference of time required to distill over the metal.
https://www.researchgate.net/figure/Calculated-vapor-pressur...
https://www.researchgate.net/figure/Fig-C1-Vapor-pressure-fo...
https://www.researchgate.net/figure/apor-pressures-of-potass...
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Radiums Lab
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Mr green guy isolated Na from Al in small quanities.
Water is dangerous if you don't know how to handle it, elemental fluorine (F₂) on the other hand is pretty tame if you know what you are doing.
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metalresearcher
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Well, at 883C the vapor pressure of Na should be 1 bar as Na boils at that temperature.
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clearly_not_atara
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Na+ ion is similar sized to O2- ion while K+ ion is too big, so the lattice energy is lower.
NaOH: -425.9 kj/mol
KOH: -424.7 kj/mol
Granted this is a small difference. But in light of the difference in ionization energy having the opposite sign, it should be a clue that there is
more to the story here than just the usual reactivity series. It is known that "NaMgO" phases form in this rxn and the compatibility of Na+ with the
lattice is probably a contributing factor. For this reason some creativity is used to facilitate the isolation of sodium.
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