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

Abstract

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.

Spectroscopic evidence for a gold-coloured metallic water solution

“…The relatively long lifetime of several seconds of the metallic water layer is partly due to the presence of the underlying alkali metal providing excess electrons in a quasisteady state manner; this is similar to our earlier experiments, where putting sodiumpotassium alloy next to a water drop led to transient formation of a blue electrolyte layer of hydrated electrons at elevated temperature 13 . In addition, it is plausible that hydrated electrons become less reactive and thus longer-lived upon delocalization in the metallic regime.…”

“…Analogous metallic solutions of liquid ammonia, which may serve in many respects as a proxy to water, have been characterized previously [6][7][8][9] . However, it is a textbook knowledge that dissolution of alkali metals in water leads to an explosive chemical reaction 10,11 , thus aqueous solutions with only low (sub-metallic) electron concentrations have been prepared so far [12][13][14] . We have now found a way around the explosive chemistry by adsorbing water vapour at a pressure of about 10 -4 mbar onto a train of liquid sodium-potassium alloy drops ejected from a nozzle into a vacuum chamber.…”

NaK alloy: underrated liquid metal

“…68 Nevertheless, the vigorous reaction of alkali metals with water can be performed in non-exploding manner by gently placing a drop of the NaK alloy on the water surface. 69 Mason et al discovered this method using a combination of high-speed camera imaging and visible/near-infrared and infrared spectroscopy to observe and characterise the system at each stage of the reaction (Fig. 5).…”

Anorganische Chemie 2016: Hauptgruppenelemente

“…Bei Raumtemperatur reagiert (80) als Elektrophil mit CO zurück zu (79). 64) Der terminale Phosphinidenkomplex von Mangan, [(η 5 -C 5 H 5 ) -(OC) 2 Mn= PN (Mes*) B (tBu) Cl], entsteht durch Zugeben von ClPNMes* zum terminalen Borylenkomplex [(η 5 -C 5 H 5 ) (OC) 2 Mn= -B tBu]. 65) Die dreifache Funktionalisierung von Phosphan mit NIiPr (NIiPr = 1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidenamino) führt zu P(NIiPr) 3 , einen bei Raumtemperatur stabilen Feststoff, der mit CO 2 ein Addukt bildet.…”

“…6) Die ungewöhnliche Bindungssituation ergibt sich aus den starken σ-Donorund π-Akzeptoreigenschaften der cAAC. Überraschenderweise ist (2) unreaktiv gegenüber H 2 , Boranen und Borhydriden, und die Reaktionen mit Selen und CO 2 führen zum Selenon (4) beziehungsweise zum zwitterionischen Carboxylat (5).…”