Rubidium (Rb) is a highly reactive metal and can be stored only under inert conditions, normally sealed in a glass ampoule, most likely under vacuum.
At first, the rubidium ampoule was broken with a special hammer. There was some white smoke (probably rubidium hyperoxide-RbO2), but Rb remarkably did not ignite at ~20oC in dry air.
Rb(s) + O2(g) → RbO2(s)
Then, rubidium was let to react with water. Because of large amounts of alkali metal (~50 g), the reaction was carried out in outdoors. In this experiment video, different varieties of the reaction of rubidium with water were presented.
Rubidium reacts with water, yielding rubidium hydroxide (RbOH) and hydrogen:
2Rb(s) + 2H2O(l) → 2RbOH(aq) + H2(g)
or in ionic form:
2Rb(s) + 2H2O(l) → 2Rb+(aq) + 2OH–(aq) + H2(g)