A dangerous but among school kids all-time favorite experiment demonstrating an explosive chemical reaction is throwing a piece of sodium in water. Every high school chemistry teacher knows that the explosion is due to release of electrons from the metal to water accompanied by formation of steam and molecular hydrogen, which can ignite during this exoergic process. The very same gases should, however, separate the reacting metal and water and thus quench the reaction. How come that the explosion occurs anyway? Using ultrafast cameras and ab initio as well as force field molecular dynamics simulations we have discovered a hitherto unknown primary mechanism of the explosive behavior of alkali metals in water. Namely, after migration of electrons from the metal to water the former acquires a huge positive charge. Thanks to mutual repulsion of these charges the metal undergoes a Coulomb explosion accompanied by ejection of metal spikes into water. This enables effective mixing of reactants, which is a necessary condition for the explosion. As bonus, we also show how to run this reaction in a non-explosive way. As a result, blue solvate electrons formed during this reaction can be observed with a naked eye and their stationary optical spectrum recorded despite their sub-millisecond lifetime in water. Mason, P.; Uhlig, F.; Vanek, V.; Buttersack, T.; Bauerecker, S.; Jungwirth, P.: Coulomb Explosion during the Early Stages of the Reaction of Alkali Metals with Water. Nature Chemistry, 7, 250 (2015). Mason, P.; Buttersack, T.; Bauerecker, S.; Jungwirth, P.: A Non-Exploding Alkali Metal Drop on Water: From Blue Solvated Electrons to Bursting Molten Hydroxide. Angewandte Chemie, 55, 13019 (2016)

Exploring the structure, dynamics and reactivity of solvated electrons: From alkali metal-water explosions to non-explosive ways

254th National Meeting (2017)

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