Low water acids
I was wondering about the behaviour and reactivity of the polyacids/mixtures of simple strong acids with their anhydrides/acid oxides.
Sulphuric acid.
Oleum is well known, and sulphuric acid is miscible with either water or sulphur trioxide in any ratio. Except when a solid precipitates. And a
general rule is that while boiling point maxima do not have a simple stoichiometric composition - water/sulphur trioxide seems to have only 1 boiling
point maximum, at 1 atm containing 1,7 % water and boiling at 330 Celsius - and neither do the freezing point minima, the freezing point maxima do
have simple stoichiometry. These are water, sulphuric acid tetrahydrate, sulphuric acid dihydrate, sulphuric acid monohydrate, pure sulphuric acid,
disulphuric acid - and what next?
A complicating matter is that dry sulphur trioxide easily gives several metastable solid and liquid forms.
Between disulphuric acid (melting point +36 Celsius) and gamma-sulphur trioxide (melting point +17 Celsius), there is a freezing point minimum
slightly under 0. But are there any further freezing point maxima? Can trisulphuric acid or any higher polysulphuric acids be isolated as solids?
How about making oleum with the solid alpha and beta sulphur trioxide? Can they be made to dissolve and recrystallize in equilibrium with oleum at
room temperature?
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