A Non-Exploding Alkali Metal Drop on Water: From Blue Solvated Electrons to Bursting Molten Hydroxide

Alkali metals in water are always at the brink of explosion. Herein, we show that this vigorous reaction can be kept in a non‐exploding regime, revealing a fascinating richness of hitherto unexplored chemical processes. A combination of high‐speed camera imaging and visible/near‐infrared/infrared spectroscopy allowed us to catch and characterize the system at each stage of the reaction. After gently placing a drop of a sodium/potassium alloy on water under an inert atmosphere, the production of solvated electrons became so strong that their characteristic blue color could be observed with the naked eye. The exoergic reaction leading to the formation of hydrogen and hydroxide eventually heated the alkali metal drop such that it became glowing red, and part of the metal evaporated. As a result of the reaction, a perfectly transparent drop consisting of molten hydroxide was temporarily stabilized on water through the Leidenfrost effect, bursting spectacularly after it had cooled sufficiently. The vigorous reaction of alkali metals in water was kept in a non‐exploding regime through gently placing a drop of Na/K alloy on water. Initially, solvated electrons are produced (blue color), before the exoergic reaction leading to H2 and OH− heats the drop such that it becomes red, and part of the metal evaporates. A transparent drop of molten hydroxide is then temporarily stabilized on the water through the Leidenfrost effect before bursting spectacularly.