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itchyfruit
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As the aforementioned pieces of K metal are soon to be the property of yourself i'm sure you'll work it out for good or bad 
But i am interested for future reference is it ok to cut K under yellow LIQ paraffin that's used for oil baths ?
The reason i ask is i have quite a lot of this(but no oil bath) and the lady in my local chemist is getting suspicious about my LIQ paraffin
purchases.
BTW just PM me a list of the other bits you want, i can't be arsed to do another list!!!!
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bahamuth
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You can cut your K metal under any hydrocarbon solvent that is water and oxygen free, but your liq. paraffin might be a little tedious to wash away
when you want your K metal for an experiment.
You want to cut it under some kind of "semi" volatile hydrocarbon, like toluene, xylene or petroleum ether bp. 60-80 or bp. 80-100. Outdoor cooking
stove purified gasoline (heptane & its isomers) works great.
Any sufficiently advanced technology is indistinguishable from magic.
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len1
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Of course, you can do anything, the question only is if the consequences you get are what you want. The potassium after being cut needs to be removed
from under the inflammable solvent, which gives you a potassium/air/hydrocarbon surface - if that has not already been achieved during sloshing of the
solvent while cutting it. Small pieces of potassium often autoignite in air - that is what pyrophoric means. If its just potassium there will be a
light puff, a lightening on the surface of the K due to the protective oxide formed, and that will be the end of it. Under toluene/xylene that will
only be the start of it due to the ensuing fireball.
K will also autoignite under kerosene if touched by anything with the slightest moisture content - such as a knife blade.
Pyrophoric metal and inflammable solvent is a bad mixture.
If anyone wants to follow the stupid advice above, you have been warned.
[Edited on 25-1-2010 by len1]
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a_bab
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Potassium metal in the amounts you have there could be disposed off in the snow (providing you have it). I'd say something like up to 5-10 grams at
once works great and it's safe.
Just toss in piece by piece outside in the snow; the potassium take fire very fast even if there is parafin oi on it, and burns quietly with no
explosions. If you did this in your garden, you'll recover some of the potassium in your vegetables later in the summer
On the other hand just as len1 said, I feel quite nervous just about the thought of having the potassium in something else than parafine oil. Some
would even go for ligroin. It's quite pyroforic; it takes fire in the air almost like WP.
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bahamuth
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Tried to provide a means for the recovery of, even if cheap, Potassium, to remove the oxide layer and get fresh potassium.
Just delivered what I have learned and read, in "Hazardous laboratory chemicals disposal guide by Margaret-Ann Armour" in the section concerning
Potassium.
If he want to get rid of it, throw it in a lake or something and enjoy the bang, easypeasy.
If recovery was to be made, how do you len1, propose it to be done, and how do they do it in the laboratory when they want fresh exposed K?
Not nearly as reactive, sat for hours cutting about a kilo of Sodium this way under petroleum ether bp. 60-80 C.
Edit:
The more I read this tread the more anxious I get, was not worried by my potassium metal before, had respect, but now, sort of worried....
[Edited on 25-1-2010 by bahamuth]
Any sufficiently advanced technology is indistinguishable from magic.
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12AX7
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Scroll down to paragraph 6, line 21:
http://204.232.255.211/30/12.html
The Chemical History of a Candle
Michael Faraday
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I am going, then, to burn this potassium in the carbonic acid, as a proof of the existence of oxygen in the carbonic acid. [In the preliminary process
of heating the potassium exploded.] Sometimes we get an awkward piece of potassium that explodes, or something like it, when it burns. I will take
another piece, and now that it is heated I introduce it into the jar, and you perceive that it burns in the carbonic acid ... |
("Carbonic acid" erroneously referring to the gaseous anhydride, CO2.)
Oh, for the days when lectures were fun.
Tim
[Edited on 1-25-2010 by 12AX7]
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len1
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Yes I rather thought your experience was more with sodium - but one should never think of the two metals as the same thing.
My method to rid K of its crust is to heat it under paraffin to 70C, the insert a 50ml volumetric pipette with short inlet preliminarily flushed with
argon so it punctures the oxide skin by 2-3mm and suction up the desired amount of perfectly clean metal. The floppy gray-blue oxide 'skin' is left
behind. Its in none of the books, but thats typical
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vulture
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I wonder however if those referring to treating potassium that way have actually much experience with potassium? Its a completely different beast.
What you get destroying K under isopropanol is an alcohol flame in the beaker. If by any chance you happen to be mad enough to pour it straight out of
the bottle into the beaker then the flame will most likely take up the bottle as well. Cutting K under xylene is like playing russian roulette, small
pieces of K are pyrophoric and you get a mixed K/xylene fire. Have a big bowl of sand or salt plus strong nerves at the ready. |
Yes, I cut up to 6g of K into small 2x2mm pieces every two months. No problem at all.
As for destroying K, I did not say you should pour pure iPrOH onto it. Hexane and then adding drops of iPrOH to the hexane works fine.
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K will also autoignite under kerosene if touched by anything with the slightest moisture content - such as a knife blade. |
I have no idea where you get this outrageous claim. I always take blocks of K out of the parrafin using a knife which has been exposed to air. After
cutting, the K & Na go into THF which comes from a fresh bottle, but obviously isn't moisture or oxygen free. Neither does this autoignite. In wet
diethylether you get vigorous bubbling, sure, but no ignition.
[Edited on 26-1-2010 by vulture]
[Edited on 26-1-2010 by vulture]
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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len1
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I have no idea where you get this outrageous claim
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Experience.
And the same shows it is to be trusted more than somebodys post.
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vulture
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You do realize that your experience is also nothing more than something described in a post? Which gives it the same value as mine?
Are you insinuating I make this all up?
You think cutting solid K is unsafe but pipetting the molten metal is safe?
I really do not understand the aim of your scaremongering towards handling potassium.
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the insert a 50ml volumetric pipette with short inlet preliminarily flushed with argon |
You do also realize that you are contradicting your claim here of traces of moisture igniting K? Merely flushing with argon does not remove traces of
moisture.
[Edited on 26-1-2010 by vulture]
[Edited on 26-1-2010 by vulture]
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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len1
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Yes I was going to the trouble of excluding oxygen by purging my pipettes with argon, but not baking them at 150C to remove the moisture, because I
was so stupid.
Thanks for clearing this up. Now I will not have exploding pipettes anymore.
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JohnWW
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On the subject of K metal, along with Rb and Cs, together with inert gases such as argon, that reminds me: I wonder if anyone has yet succeeded in
isolating an ionic compound, containing K+ or Rb+ or Cs+, in which the alkali metal has given up its lone valence electron to either He or Ne, to form
an anion He- or Ne- which would be isoelectronic with metallic Li or Na? Such a compound would be extremely reactive, much more so than Li or Na. In
this connection, alkali-metal anions have been isolated, containing Li- or Na- or K-, but they would be more easily formed than He- or Ne- because of
the greater atomic charge and the stabilization afforded by spin-pairing in the s orbital.
The possibility has been thought of, e.g., regarding hypothetical cesium neonide, see http://www.eric.ed.gov/ERICWebPortal/recordDetail?accno=EJ26... or http://pubs.acs.org/doi/abs/10.1021/ed059p637 , which was originally in Journal of Chemical Education, v59 n8 p637-39 Aug 1982. Also http://pubs.acs.org/doi/abs/10.1021/ed061p566.4 . If it could be produced, it would mean that K, Rb, and Cs cannot be safely handled and stored
under He or Ne, but can still be under Ar or Kr or Xe.
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vulture
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| Quote: |
Yes I was going to the trouble of excluding oxygen by purging my pipettes with argon, but not baking them at 150C to remove the moisture, because I
was so stupid. Thanks for clearing this up. Now I will not have exploding pipettes anymore. |
There is no need for sarcasm. It's not about what you know. It's about what you say in your post. You lecture others about recklessness and bad
information when it comes to handling potassium, yet you omit an essential safety procedure from your own post!
You also glossed over other important points I raised without even addressing them.
Do I really have to make a movie next time when I cut potassium to prove to you I'm not selling BS? Or will you also dismiss that with sarcasm without
addressing the real issue?
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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turd
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I can also not relate to the inherent danger of potassium. We used it to dry THF for many years and treated it just like sodium. We even used the same
rusty butter knife for both metals.  Maybe we were just lucky, but nobody ever
caught fire. The big advantage of K over Na is of course that there is no need to make small pieces. Now NaK I hear is an entirely different matter,
but unfortunately I've never seen it in action - maybe I should make some one day (in an ampoule).
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vulture
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| Quote: |
I can also not relate to the inherent danger of potassium. We used it to dry THF for many years and treated it just like sodium. We even used the same
rusty butter knife for both metals. Maybe we were just lucky, but nobody ever
caught fire. The big advantage of K over Na is of course that there is no need to make small pieces. Now NaK I hear is an entirely different matter,
but unfortunately I've never seen it in action - maybe I should make some one day (in an ampoule). |
We use Na-K alloy to dry THF and ether. It is prepared by cutting the Na and K and putting them in the respective solvent. The alloy doesn't form
until the solvent is refluxed, after which it forms silver globules which keep a fresh layer on the outside and stay liquid at RT. Obviously this
should be kept under argon at all times.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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entropy51
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What's the big deal about Na-K? It has been used to cool computers.
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turd
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Quote: Originally posted by vulture  | | We use Na-K alloy to dry THF and ether. It is prepared by cutting the Na and K and putting them in the respective solvent. The alloy doesn't form
until the solvent is refluxed, after which it forms silver globules which keep a fresh layer on the outside and stay liquid at RT. Obviously this
should be kept under argon at all times. |
What's the advantage of keeping it liquid at RT? That it keeps the THF dry over night?
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JohnWW
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The eutectic alloy Na-K composition is liquid at room temperature. It consists of 78% potassium and 22% sodium, is liquid from −12.6 to 785 °C,
and has a density of 866 kg/m³ at 21°C and 855 kg/m³ at 100°C, lighter than water. The entire composition range of 40% to 90% K is in fact liquid
at room temperature. See http://en.wikipedia.org/wiki/NaK .
Uses for it, e.g. as a liquid coolant in heat exchangers, with a thermal conductivity much greater than that of water (but cheaper and lighter and
more conducting than Hg or Ga) have been based on this property, particularly in experimental fast-neutron nuclear reactors. It could also be used in
thermometers. However, of course, it suffers from the disadvantage of being dangerous if exposed to moisture or alcohols (or several other types of
highly polar organic compounds) or any gas other than the elemental inert gases. It also has only about 1/4 of the thermal heat capacity of water, and
a high surface tension.
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turd
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Huh?
That didn't answer my question at all. I wanted to know what the advantage of using NaK/THF over K/THF is, given that K is also liquid in refluxing
THF.
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