metalresearcher
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KOH with Mg metal
Yesterday I posted a movie with KOH + Al metal.
The reaction was lousy..
Now I repeated it with Mg metal and was far more spectacular.
<iframe sandbox width="525" height="424" src="http://www.youtube.com/embed/N-ij-jo22bw?hl=en&fs=1" frameborder="0"
allowfullscreen></iframe>
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condennnsa
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Hmmm, does this reaction reduce KOH all the way to potassium?
I remember that Nurdrage was also working on a video of making sodium by reducing NaOH 'aluminothermically' with magnesium, and then heating the
resulting mess in mineral oil to separate the sodium, claiming only about 10% Na yield.
I also tried the NaOH one, which is a more violent reaction than the KOH, but I didn't bother to try and separate whatever sodium might have formed, I
just threw it in the water. It did react very vigorously, but not so much, so I suspected that I might have ended up with a lot of sodium hydride
instead? which will also react with water similar to sodium metal ? NaH + H2O -> NaOH + H2 I also suspect that if any alkali metal will form, a big
part of it will boil away during the high temperature reaction...
but since pok's potassium method is yet to be proven to work with sodium, it might be worthwhile looking into as a non electrolytic way to Na metal.
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BromicAcid
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I've used this method before to make potassium metal and I am sure it's been discussed somewhere else on this forum before. The problem with the
reaction is that nearly all the KOH you come across will be a 85% technical grade with the remainder of the material being water.
So if you're using 100 grams of this KOH, you have 85 g (1.51 mol) KOH and about 15 grams (.833 mol) water. That water can directly react with your
magnesium at elevated temperatures or kill off your final product by reverting to starter. In the latter case you're looking at the theoretical yield
of this reaction to be less than half of what it looks like initially on paper. Plus you have poor mixing and heat transfer to contend with which
greatly increases the amount of material that never even reacted (the thread on benzene from benzoate and base addresses some of the work arounds for
this). If you run this reaction and see the slag and garbage that can come out of it then you know what I am talking about.
When they did this 'back in the day' they used various different reagents. Lead and sodium chloride was one of them and then distill off the sodium.
Potassium and... actually I can't remember off the top of my head but magnesium and potassium carbonate could lead to explosions IIRC. Nevertheless,
the reaction works but it is not optimal.
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AndersHoveland
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It is quite possible that elemental potassium is being produced, which would immediately be vaporized out and burn on contact with air. Although
potassium is usually considered a more "reactive" element than magnesium, for example displacing magnesium from magnesium chloride, the formation of
MgO is favorable for a number of reasons: crystal lattice energies of the final product, slightly covalent/stronger Mg-O bonds, double charged oxide
ions (in K2O) being less favorable because of the small atomic orbital diameter, and Le Chatelier's Principle. Possible reactions are:
(2)KOH + Mg --> K2MgO2 + H2
(2)KOH + (2)Mg --> (2)MgO + K2 + H2
However, the reaction between aqueous potassium hydroxide and magnesium involves a completely different reaction, similar to the reaction
between potassium hydroxide solution and aluminum. The presence of potassium hydroxide apparently increases the solubility of magnesium hydroxide,
suggesting that magnesium hydroxide is very slightly amphoteric. In fact, magnesium metal very slowly corrodes in plain water, and fairly rapidly in
boiling water. In this case, the potassium hydroxide could be said to catalyse the reaction of solid magnesium with water.
This thread really belongs in the general chemistry section.
[Edited on 19-9-2011 by AndersHoveland]
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