Chemical reactions of the elements

Reaction of rubidium with air

Rubidium is very soft and easily cut. The resulting surface is bright and shiny. However, this surface soon tarnishes because of reaction with oxygen and moisture from the air. If rubidium is burned in air, the result is mainly formation of dark brown rubidium superoxide, RbO2.

Rb(s) + O2(g) → RbO2(s)

Reaction of rubidium with water

Rubidium metal reacts very rapidly with water to form a colourless solution of rubidium hydroxide (RbOH) and hydrogen gas (H2). The resulting solution is basic because of the dissolved hydroxide. The reaction is very exothermic. The reaction is so fast that if the reaction is carried out in a glass vessel, the glass container may well shatter. The reaction is slower than that of caesium (immediately below rubidium in the periodic table), but faster than that of potassium (immediately above rubidium in the periodic table).

2K(s) + 2H2O → 2KOH(aq) + H2(g)

Reaction of rubidium with the halogens

Rubidium metal reacts vigorously with all the halogens to form rubidium halides. So, it reacts with fluorine, F2, chlorine, Cl2, bromine, I2, and iodine, I2, to form respectively rubidium(I) bromide, RbF, rubidium(I) chloride, RbCl, rubidium(I) bromide, RbBr, and rubidium(I) iodide, RbI.

2Rb(s) + F2(g) → RbF(s)

2Rb(s) + Cl2(g) → RbCl(s)

2Rb(s) + Br2(g) → RbBr(s)

2Rb(s) + I2(g) → RbI(s)

Reaction of rubidium with acids

Rubidium metal dissolves readily in dilute sulphuric acid to form solutions containing the aquated Rb(I) ion together with hydrogen gas, H2.

2Rb(s) + H2SO4(aq) → 2Rb+(aq) + SO42-(aq) + H2(g)

Reaction of rubidium with bases

Rubidium metal reacts very rapidly with water to form a colourless basic solution of rubidium hydroxide (RbOH) and hydrogen gas (H2). The reaction continues even when the solution becomes basic. The resulting solution is basic because of the dissolved hydroxide. The reaction is very exothermic. The reaction is so fast that if the reaction is carried out in a glass vessel, the glass container may well shatter. The reaction is slower than that of caesium (immediately below rubidium in the periodic table), but faster than that of potassium (immediately above rubidium in the periodic table). As the reaction proceeds, the concentration of base increases.

2K(s) + 2H2O → 2KOH(aq) + H2(g)

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