Why is sodium dripped into ethyl alcohol
The information given here has been compiled to the best of our knowledge and belief. Hopefully they will help, but unfortunately they cannot guarantee their accuracy or completeness. In particular, they do not release you from independent research and decision-making with regard to the measures to be taken when dealing with hazardous substances. Notes, feedback and questions are welcome.
Not just "like sodium" but in a completely different league!
Even if you simply leave a closed potassium bottle standing, the potassium gradually develops crusts under the protective liquid, which contain highly explosive peroxo compounds (K2O2 and KO2) may contain. Even light pressure, e.g. when lifting pieces of potassium with pliers or trying to cut with a knife, can trigger an ignition or even an explosion. Yellow or red crusts in particular are extremely dangerous.
Potassium with colored crusts must no longer be used! No pieces may be removed - not even to destroy them!
As far as possible, potassium should be prevented from becoming too crusty. This includes:
- Obtain only small batches that are used up quickly enough.
- Check ordered batches upon receipt and reject encrusted ones.
- Leave the material in the original manufacturer's bottles. If you still have to decant, use break-proof glass bottles with a plastic coating. Plastic bottles are unsuitable because they can be gas-permeable, which can lead to a gradual ingress of oxygen.
- Only use absolutely clean and guaranteed water-free devices (e.g. knife, crucible tongs) to handle potassium.
- Do not take potassium out of the storage container for cutting but cut it under protective liquid.
- Pieces extracted from the protective liquid may no longer be returned to the storage bottle.
- The stored potassium must never protrude from the protective liquid. Additional protective liquid must be added free of air bubbles.
- Easily evaporable protective liquids are to be avoided. Paraffin oil is suitable.
- After removing potassium from the storage vessel, flush the gas space above the protective liquid with argon, then immediately close the vessel. Without argon protective gas, the dangerous crusts develop faster!
- Only use containers with tightly fitting lids. Have a replacement cover ready in the event of a cover defect.
- Since removing potassium from the storage jar is an inherently dangerous operation, work under the fume cupboard and make sure that the sash is pulled down so that it completely shields your face and your upper body as widely as possible! It may be better to sit on a laboratory stool. Your arms may then be in a lower position and you can close the sash further.
- All the equipment you need must be within easy reach and you must be able to perform all operations safely without dislocating yourself or suddenly missing another arm.
- Wear a laboratory coat made of non-easily inflammable fabric (cotton)! The danger threatens from the front, so the laboratory jacket must be closed!
- Safety glasses are mandatory.
- Wear two gloves on top of each other! The air cushions in between may provide a certain amount of heat protection. However, there are no reliable studies on this. Note that a latex glove is not resistant to the protective liquid.
What to do when it's too late
Existing potassium stocks become more and more dangerous through storage. The deactivation described below is then no longer safe! If the crusts aren't all that bad, you might be lucky to find a waste disposal company that will discreetly but for a fair bit of money take the stuff for you. If the crusts get even thicker, there is no longer any discreet solution: The only possible disposal is then to have the material removed by trained special forces who, with great interest from the local press, pull up in front of your school with many blue light vehicles and presumably in the potassium bottle embed in a large sand container and burn it down in a specially dug up sand pit in a safe place or detonate it with the addition of explosives. The final option is that you'd rather put it in the back of the corner until Santa's day, and risk the bottle igniting at school at some point. Then even more blue light vehicles drive in front of the school, not only to transport injured or even dead people and to combat the consequences of the fire or explosion, but also to determine who was responsible for what happened.
Another thing you should know: You have no real option to put out burning potassium! All types of extinguishers available at a school are not suitable for this! The carbon dioxide extinguisher even works as a fire accelerator! You can pour fire-fighting sand on it, but this only works if the burning potassium is so good that you can pour over a heap of sand that covers everything and if you are good at "throwing sand", because you will not stand directly next to or even over the flames want. It is more realistic that you have to let the potassium burn off and, if necessary, prevent or delay the area around the potassium from being set on fire. Expect that you don't trust yourself to do it or that you shouldn't trust yourself to do it and better evacuate the building.
Potassium reacts considerably more explosively than sodium and is therefore much too violent with ethanol or isopropanol. Use 2-methyl-2-propanol for destruction (tert-Butyl alcohol)! Note that the reaction may initially be inhibited by incrustations in the metal. Potassium tends to form nests that can last for a long time. Only when the mixture gradually reacts more and more sluggishly can isopropanol or ethanol be carefully added.
Since ignition can never be safely ruled out even with the most careful work, working under inert gas protection is considerably safer. Do not use open, wide-necked vessels such as a beaker.
- Do not cool the reaction vessel in the ice bath. If the piston breaks - and this can happen once due to the possible thermal loads here, the metal comes into contact with water with the known consequences!
- Unfortunately, a fairly large excess of solvent has to be used in the destruction. False thrift can be very dangerous here. The mixture quickly thickens due to the alcoholate that forms in a syrupy manner. This severely disrupts the necessary heat dissipation. In extreme cases, a locally reacting potassium nest can heat up locally until glowing and ignite the entire mixture! For this reason, too, cooling in an ice bath does not make sense, because the thickening of the mixture then only starts all the faster! Always keep the mixture thin! It goes without saying that the potassium should be added to excess alcohol and not the other way around, the alcohol should be dripped onto the potassium!
- In the case of residues that are, for example, in a reaction vessel and cannot be completely removed from there, a sufficient amount of inert solvent must first be added to maintain the necessary cooling and mixing, to which the alcohol can then be added dropwise .
- Be sure to monitor the mixture until the reaction is complete!
- Do not break the disposal "above the knee"! Take enough time! The slower the mixture reacts, the safer it is.
After the reaction, let stand at least overnight. Then carefully dilute further with ethanol and finally with water, always paying attention to whether a reaction can be observed after the addition. Then leave it for another night!
Even with the greatest precautions, the reaction is dangerous. Take all precautions to be able to effectively combat any spontaneous ignition that may occur at any time. (e.g. safety tub, extinguishing agent, exclusion of other highly flammable substances in the vicinity.)
Ensure that the resulting hydrogen gas is safely discharged (exhaust) and pay particular attention to all devices and containers used, which can only be considered metal-free when they have been completely immersed in water and free of air bubbles after the treatment described! The nests of potassium are insidious! It's not just hypothetical, but it regularly happens that a flask in which you have decomposed potassium by letting it stand for days as described and finally even added water and left it to stand again, when finally rinsing the emptied flask with water, a jet flame again drives out!
According to the specifications of the RiSU, the mixture must be carefully disposed of in the wastewater. For quantities> 100 ml, it is strongly recommended that the mixture be poured into a smaller container in portions beforehand, because the potassium deposits that are still present can cause ignitions when pouring out. It is better if only the contents of a small beaker are on fire and not, for example, the entire 2-liter vat.
Why does it have to be potassium?
Against the background of the explosive nature of potassium, it is surprising that the use of potassium in schools is not prohibited by the RiSU or the list of substances for the RiSU (DGUV-I 213-098). In 2008, Bundeswehr soldiers and fire brigades visited various schools with high media interest in order to remove the picric acid present there and, as described above for the potassium, to blow it up in a protected place. Back then, hysteria was certainly also involved, because with a little water phlegmatized picrics is as peaceful as powdered sugar again. This option does not exist with potassium! If the crusts are thick and they are also colorful, you no longer have your own option!
Urgent advice: don't play the hero! You are not only a good teacher if you trust how to handle potassium. In addition, other qualities are more important.
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