Big Reaction: Cesium and water

I’m a sucker for beautiful color.

This reaction shows cesium dropping into water that contains phenolphthalein. The phenolphthalein (C₂₀H₁₄O₄) acts as an indicator, turning pink when the solution turns basic. In this case, the base is CsOH, a product of 2H₂O + Cs → 2CsOH + H₂

The pulsed reaction is due to the phenomenon of cavitation. As the chemical reaction progresses, a bubble of heated water vapor forms, slowing the reaction. The cavity implodes as it cools, leading to another pulse of reaction and more cavitation.

Here’s the original video, from SciencePhotoLibrary:

More on why alkali metals explode. And more fun with Cesium.

Have a neat chemical or physical reaction you’d like to share? Tell us in the comments!