Rubidium hydrogen sulfate

Rubidium hydrogen sulfate is the rubidium salt of sulfuric acid. It has the formula RbHSO4.
Synthesis.
It may be synthesised with water and a stoichiometric amount of rubidium disulfate. Reaction takes place where there is no humidity:
There is another method of creation. It is similar to the synthesis of sodium sulfate and potassium sulfate. This reaction requires rubidium chloride and a little bit of warm sulfuric acid. Some hydrogen chloride is also produced during the reaction.
Properties.
It is a hygroscopic compound. It has a monoclinic crystal structure, its structure is P21/n. Dimensions of the unit cell are: a = 1440 pm, b = 462.2 pm, c = 1436 pm and β = 118.0°. Its crystals are isomorphs with ammonium hydrogen sulfate crystals.
Its standard enthalpy is −1166 kJ/mol. During its dissolution in water, there is 15.62 kJ/mol energy produced.
After warming up it decomposes to rubidium disulfate and water:
Like potassium and caesium, rubidium has another hydrogen sulfate compound as well: Rb3H(SO4)2.