Caesium in Water (slow motion) - Periodic Table of Videos - We've always been a bit unlucky about the reaction of cesium and water. We've tried it several times. It's meant to go explosively. But always, it's been a bit of a disappointment, sometimes a real disappointment. [LAUGHTER] We decided we would try a quick experiment to see cesium react with water using a high speed camera. This is just a quick demonstration to see what happens. This is not a carefully controlled scientific experiment. Of course, it's controlled so it's safe, but we haven't fixed every parameter in the way that you would do if you were doing a carefully adjusted experiment. Because high speed filming needs very bright lights, the heat of the lights made so that the cesium, which has a low melting point, was nice and liquid before we broke the apple. When you break the apple, the shock of breaking it broke up the cesium into quite a few little droplets. And you can see these droplets spreading out and falling towards the water. [MUSIC PLAYING] What was surprising is that you can see these individual droplets of metal have a vapor trail. They're clearly reacting with something in the air. It could be with the oxygen, but we think it's probably due to the water vapor. With the hot lamps, there's quite a lot of vapor coming from the water. So the reaction between cesium and water begins in the gas phase with, essentially, the water vapor that is above it. And then when these droplets hit the water, each of the droplets starts reacting quite violently. It's important to stress that reactions between molten metals and water are very well studied. There are a whole series of papers. I've got one here, which Brady likes, first of all, because it's from the journal Nature. The reason he likes it is it's from 1973, three years before he was born. [MUSIC PLAYING] Now, of course, I'm a chemist, so we come back to the chemistry. And cesium reacting with water should make the water alkaline because we're making cesium hydroxide, cesium plus ions OH minus ions. And therefore, the water should be alkaline. So you might ask yourself, what would have happened if we had put an indicator into the water before we did the explosion? So we only thought about it afterwards. But luckily, we still had rubidium to react. So we have tried rubidium with an indicator. Keep watching to see what happened for us. You may have seen videos on the internet where people say they're reactions of cesium, and I've been told on quite good authority that, occasionally, rubidium has reacted better, and they've switched the film. So what is labeled cesium on the film may actually be rubidium. We get lots and lots of emails from our viewers, and we try our best to answer at least some of them. But some of them make points which are quite difficult to explain why they're wrong without pages of explanation. And we're not experts in some of these fields anyway. But if you send us an email and we don't respond, this is not because we're ignoring what you're saying but just because we're human and we can't answer everything.