Chemists have scrutinized a classic piece of bench chemistry — the explosion that happens when sodium metal hits water — and revised the thinking of how it works.
On contact with water, the metal produces sodium hydroxide, hydrogen and heat, which was thought to ignite the hydrogen and cause the explosion. To delve into this, Pavel Jungwirth at the Czech Academy of Sciences in Prague and his team used high-speed cameras to capture the reaction of a drop of a liquid alloy of sodium and potassium with water at room temperature.
They found that spikes of the metal shoot out from the droplet just 0.4 milliseconds after it enters the water — too fast to have been expelled by heat. Computer simulations revealed that sodium atoms at the surface of a small cluster each lose an electron within picoseconds. The positively charged ions rapidly repel each other, causing the explosion, while the protruding metal spikes generate new surface area that drives the reaction.
Nature Chem. http://dx.doi.org/10.1038/nchem.2161 (2015)