Synthesis Of Elemental Potassium.

[aaron1999]

A few days back I requested information on synthesis of potassium metal using electrolysis of molten Potash on this 'blog'. I received an answer from Teddio, (thank you Ted). But now i would like to know if it were possible to do that by-
Mixing 4 grams of KOH with 5 grams of Mg, in a stainless steel reaction vessel. Then i cover the lid with a heavy object while placing an ignition cord inside(i small bit hanging on the outside though). Then i ignite the cord..which inturn hopefully ignites the magnesium, which while burning..bonds with the oxygen in the KOH, leaving pure elemental potassium(in some ***). After the potassium enriched *** has cooled...i remove the lid and pour in some mineral oil. Then i add some water to a jug and i add an almost equal amount of mineral oil on the top. Now i add the *** slowy to the water-mineral oil. The *** will sink down below the layer of oil, into the water. The Kallium present in the *** will react with the water and will rise up into the mineral oil layer where it will stay trapped until i pick it out.
I am fully aware if the safety hazards, i would like to know if this works.

[gen2]

In a word: NO

Magnesium is lower down the reactivity series than potassium so the oxygen will remain bound to the potassium.

[aaron1999]

gen2 i doubt the reactivity plays a factor. This process was used to make elemental sodium...and sodium too has a higher reactivity or you can say..is more electropositive, than magnesium. Check the link as proof.

http://www.youtube.com/watch?v=seSg_GWj1b0

[theprof]

Let's leave aside the reactivity series and look at this from another angle. I'll point out a few things to you and we'll progress from there.

I'd suggest to you that igniting magnesium ribbon in this way is fraught with difficulties. Yes, we've all seen the school lab experiments but potentially oxidised magnesium ribbon (which most of it is depending on age) would hinder the whole project. Magnesium ribbon is not suitable. Fresh ingot shavings would work but sourcing them would be problematical. Incidentally, removing oxidised magnesium from magnesium ribbon is virtually impossible to do properly.

What type of reaction vessel are you considering using?

You talk about "potassium enriched ***" but are not specific about the temperature it needs to cool too before you add the mineral oil? What temperature would you consider suitable?

You've not provided any information on the "mineral oil" you propose to use. A word of warning: the stuff you need is totally anhydrous and standard or technical mineral oil does not meet these requirements. If you use pharmacy/drugstore types of oil, it's certain that the potassium will ignite and possibly even detonate with horrendous consequences. Remember "mineral oil" does not have a precise chemical composition and in general terms, can be regarded as a random mix of alkanes. Such a mix cannot be considered to be totally anhydrous. There are other more suitable “oils” for this purpose, none of which you are likely to obtain unless you have an account with Sigma-Aldrich and the necessary permits.

(continued)

[theprof]

Be aware of the extreme danger of formation of the superoxide. You risk blowing yourself to smithereens if the superoxide occurs. I suggest you research how the mineral oil and superoxide might interact and bear in mind handling techniques including vacuum chambers or oxygen-free atmospheres.

Finally, there’s the issue of storage. You can’t store elemental potassium under bog-standard mineral oil for any length of time. If air infiltrates the container, the consequences can be dire. Plastic screw caps do not provide security in this respect. Any trace of black elemental potassium in the oil is an indication that it’s time to run for the hills.

If you have any serious, mature points to ask regarding the above, I’ll explain in more depth. Nevertheless, my advice to you is to not to try what you propose at home as you could be seriously injured.

[Teddio]

The greater electropositivity of potassium compared to magnesium is not the only consideration when considering whether such a reaction is possible: there are many other factors including the high lattice energy of the MgO product. This reaction certainly works. You will need anhydrous KOH and finely powdered magnesium, and be aware that any potassium metal produced in air will oxidise immediately to potassium oxide.
Technically it will be difficult to achieve a good yield of potassium metal. As I said before, take appropriate safety precautions.