Chemical Properties of Potassium

Potassium is a very reactive substance, decomposing water with formation of the hydroxide so energetically as to ignite the evolved hydrogen. This phenomenon has been attributed to the free motion of the hydrogen being impeded by the high density and large molecular volume of the potassium vapour, and the consequent localization of the heat generated by the action. With sodium the hydrogen is not in ordinary circumstances ignited, since the metallic vapour has a low density and small molecular volume; although ignition of the hydrogen may be effected by keeping the sodium stationary by supporting it on filter-paper floating on water. The action of the metal on ice begins at -105° C. When exposed to air the bright surface of the metal soon tarnishes, owing to the effect of moisture. The metal also combines energetically with oxygen and the halogens, an example being the liberation of silicon and boron from their oxides and chlorides. Its solution in liquid ammonia reacts with ozone.