Description
Calcium pyrosulfate has the molecular formula of
CaS
2O
7 and the molecular weight of 216.2078 g/mol.
There are few references in the scientific literature concerning
this salt. This salt is not expected to be stable
in aqueous solution and is expected to decompose to
the sulfate. This may explain why the data on the Ca
salt is sparse to nonexistent. It can be prepared via
a solid-state reaction with ammonium pyrosulfate:
CaCl2+(NH4)2S2O7+heat
CaS2O7+2NH3(gas)+H2O(gas)
The solubility of this salt has not been reported. The
existence of hydrates is unlikely. However, if one heats
the persulfate, a pyrosulfate salt can be obtained:
2CaS2O8 2CaS2O7+O2
Further heating then forms the sulfate plus oxygen.
These reactions have not been studied critically and no
decomposition temperatures can be quoted. Another
method of preparation involves the sulfate. If calcium
sulfate is mixed with fuming sulfuric acid (to minimize
the water present), it dissolves, forming a syrup which
upon heating to 150°C deposits the pyrosulfate crystals
which are stable. Further heating removes the excess
acid. These crystals are stable to about 720°C where
they decompose to form the sulfate plus sulfur trioxide.
