Tales from the Prep Room: Alkali Metal Match

Can you light a match with water?

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Lighting a match with chemistry.

After touring with the Christmas Lectures in Japan, Andy Marmery returns to the Prep Room in a follow up video to How to Light a Match with Water.

Responding to a comment left on YouTube, he attempts to light a standard match with just a single drop of water. Using Sodium yields some success, but Andy then looks to more reactive elements further down the Periodic table...

If you have suggestions for any other experiments to try in the prep room then please leave a comment below.

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Type:
Demo
People:
Andrew Marmery
Location:
London, UK
Filmed in:
The Prep Room
Published:
2012
Filmed:
2012
Credits:

The Royal Institution / Ed Prosser

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Tales from the Prep Room

cc_by-nc-sa License: Creative Commons

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Transcript

So you might remember a little while ago, we made a film called, Lighting a Match with Water, where we heated some water and passed it through a copper coil, and then used it to light a match like this. Stick it into the stream and then withdraw it to allow the air to get to it, and at that point the match ignites.

So that was all a bit complicated and it inspired one of our YouTube followers to leave a comment, which I'll read to you. He says, why not put a bit of sodium on the end of the match and then put a small drop of water on it. So basically, can we light a match with just a single drop of water? I think is what he's getting at.

So, the first thing I thought was that it's a little bit of a cheat because it's just kind of using chemistry to light the match, which is what the match does anyway really. But the second thing I thought was, actually, I don't know what would happen. So I thought it would be nice to find out.

Here's a huge lump of sodium of which I'm going to cut a very small piece off. Nice silvery finish there. So, I'm just going to-- We have to keep it under oil because it's so reactive. I'll try not to get sodium on Bruce Hood's skull. Oh well, it's all right.

So this is a little piece of sodium. Sodium is what's called an alkali metal from group one of the periodic table. And all the alkali metals are very reactive. They react very strongly with air, which is why they're stored in oil in the jar and in here. But also very strongly with water. Wipe the oil off a bit and then damp this down. Throw it in here and we'll see what happens.

It's very exothermic so it melts. So if you look-- so it's a molten ball. So what we saw there was, well, first of all, the sodium melted with the heat from the exothermic reaction. And secondly, we saw the flame, which was from the hydrogen that was liberated by the reaction. So the hydrogen came from the water that the sodium was reacting with, ignited with the heat, and then the whole thing burned for a while and got so hot, it eventually exploded.

The question is whether we can transfer all that and get it to happen on the end of a match? Just poke it down over, our piece of sodium, like that. I think this might work, actually.

OK, so that was kind of all right. We managed to light the match using the reaction between sodium and water. I guess it wasn't a whole lot more practical than using the copper coil and the boiling steam, but there you go. But we didn't manage to light it with just a single drop of water, it took quite a lot. It would be nice to see if we can do that.

So I think the next thing to do is to move a little down the periodic table. So these are the alkali metals here, so we just used sodium. So next one on the list, K for potassium. So it's a lot like sodium in a lot of ways. It reacts very similarly, but actually reacts even more vigorously. And that's because it's outermost electron, which is responsible for the reactivity, is held on even less strongly than it is with sodium.

So we're going to do the same thing we did before with the potassium and we'll see what happens. So that was pretty good. We lit the match with just a single drop of water. If anyone else has any ideas for some useless or useful experiments they'd like to see us try in the prep room, get in touch.

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