Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Kong on February 04, 2005, 12:04:22 AM
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Ok, lets here it. I have never done any demo's with phosphorus. Seen a few. But am interested. If you don't want to post...
Thanks.
Edited-Mitch: Posting your personal e-mail online will get you spammed, so I deleted it.
Edited-Jdurg: I've just split this post into a new thread since it will probably be seen a bit better in this manner and will keep things on-topic.
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You should look in the Journal of Chemical Education. A year or two ago they had an issue that had some white phosphorous demos in it, and as I recall, it showcased one of them on the cover.
That being said, I would be very careful when dealing with this material. This is not something to be taken lightly and is not something to be done in a high school. Even if your teacher does it and is experienced, it can be dangerous. IIRC, the lethal dose of white P is 0.05g. When it burns, it forms P2O5, which is also toxic, and if it gets on your skin, the proper treatment is to pack it with mud, then cut off the skin of the affected area. There may be better ways of dealing with it now, especially in certain medical centers, but in the field or in a classroom, this could lead to some problems. I'd personally leave this demo up to some college profs.
Take this with warning, too: I think it's perfectly reasonable for a science teacher to demo pyrotechnics, thermite, and even some explosives to a class, so for me to say that I think white P demos are dangerous is saying a lot.
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The ONLY White Phosphorus demo that I've ever seen and would consider 'partially' safe is the "barking dog" demo. It's where a tall graduated cylinder is set up inside a fume hood with a high rate of air movement. Some white phosphorus is dissolved in carbon disulfide and this CS2/P solution is placed in the cylinder. It is then allowed to evaporate, and once enough of the CS2 has evaporated the White Phosphorus ignites and makes this strange barking sound. The other demos involve taking that CS2/P solution and writing on paper with it. As the CS2 evaporates, the paper burns where the solution was. Either of these are still pretty dangerous, but they are ones that I think could be done by an experienced high school chemistry teacher. (The only problem is that most high schools don't have fume hoods which are good enough or the right chemicals).
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thanks
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You could do the preparation of Hittorf's violet phosphorus reasonably safely also, certainly less dangerously than having to handle WP in carbon disulfide.
You have to dissolve some red phosphorus (which has not the acute toxicity of the white allotrope) in molten lead, in a pyrex boiling tube, using thin shavings of lead metal to hasten melting, then once the lead has solidified and cooled, dissolve it away with concentrated nitric acid.
This should leave crystalline violet phosphorus behind which can be filtered off and washed with water to free it from residual lead nitrate and HNO3.
I have heard, just from a single paper, that scarlet phosphorus results, if a catalytic amount of sodium or a sodium compound is added on melting, but I cannot account if this actually happens.
Jdurg, perhaps you could prepare some violet phosphorus for your element collection this way, as its quite a safe experiment, I would say, and uses no particularly heinous chemicals :)