Stupid question

OK, I'm taking chemistry in college. my professor told my class to bring something that can cause FIRE when put in WATER.

I did some molecule research and found that SODIUM medal can cause the effect.

Where can I buy sodium medal???

Hobby store, maybe.
My take on the assignment would also be sodium (or potassium - even more violent), but then it's been 40 years since general chemistry.

If all else fails, tell him that you were concerned with safely transporting the elemental sodium, so you combined it with chlorine to render it inert. And hand him some table salt (Salt is NaCl - sodium chloride)

Along with Sodium, group one elements on the periodic table.

Something that can cause fire when put in water? Hmm. How about a fisherman?

More seriously, though, you might find it easier to obtain quicklime: http://en.wikipedia.org/wiki/Quicklime

Anything that causes a fire in water is too unstable to be sold in normal stores. Just touching it would make it react with the moisture on your hands.

http://www.youtube.com/watch?v=JD85OUkEKKw

You could try ordering it online from a chemistry supply website. Or those in the video got it on ebay. I'm not sure but I think you have to store it in oil just to keep it away from moisture.

Yeah. I wouldn't think that you would get homework to bring something in that reacts with water.
Such things are very volatile and have to be stored in an organic (carbon and hydrogen based) solution.

Also, medal? I'm not to sure what this means, do you mean metal? Have you ever seen sodium? it is very greasy looking, not like what you would think of when you think of metal.

I am in the middle of a Chemistry based degree at uni and I find it really odd that you would need to bring something that reacts so vigorously with water to class. But I do know of other, not so nice, uses for such an element, are these perhapses more of your interest?

Magnisium? I seem to remember something about magnesium having explosive properties when combined with water...

My chemistry teacher showed it to me, how the sodium was reacting on the water, it sparked with fire and spinned around on water until it dissapeared. A very cool show!
And you only need a very small piece of sodium (like your little finger nail size), and they keep sodium soaked in the oil to prevent it exploding.
I dont know where to buy though,sorry doesnt help :p. But it must be not very easy to get it since it is a dangerous substance.