Rubidium fluoride
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Rubidium fluoride (RbF) is the fluoride salt of rubidium. It is a white crystalline solid with a cubic crystal structure, similar to common salt. It forms two different hydrates, a sesquihydrate with the stoichiometric composition 2RbF·3H2O and a third hydrate with the composition 3RbF·H2O.
Synthesis
There are several methods for synthesising rubidium fluoride. One involves reacting rubidium hydroxide with hydrofluoric acid:
RbOH + HF → RbF + H2O
Another method is to neutralize rubidium carbonate with hydrofluoric acid:
Rb2CO3 + 2HF → 2RbF + H2O + CO2
Another possible method is to react rubidium hydroxide with ammonium fluoride:
RbOH + NH4F → RbF + H2O + NH3
The least used method due to expense of rubidium metal is to react it directly with fluorine gas, as rubidium reacts violently with halogens:
2Rb + F2 → 2RbF
Properties
The enthalpy of solution of rubidium fluoride was determined to be −24.28 kJ/mol.
Rubidium fluoride has a purple or magenta red flame test.
Related compounds
In addition to simple rubidium fluoride, an acidic rubidium fluoride with the molecular formula HRbF2 is also known, which can be produced by reacting rubidium fluoride and hydrogen fluoride. The compounds H2RbF3 and H3RbF4 were also synthesized.