The disulphuric acid solvent system. Part I. Cryoscopic and conductimetric measurements on the system H2SO4–SO3 and solutions of some metal sulphates
Abstract
Freezing-point depressions produced by a number of non-electrolytes give a value for the cryoscopic constant of disulphuric acid of 5·9 deg. mole–1 kg. It is shown that the self-dissociation of the solvent can be represented approximately by the equation, 2H2S2O7⇌ H2S3O10+ H2SO4⇌ H3SO4++ HS3O10– The molecular dissociation is extensive (ca. 20%) but the amount of ionic self-dissociation is small. Sulphuric acid is a very weak base, while sulphur trioxide forms not only H2S3O10, but also appreciable amounts of tetrasulphuric acid H2S4O13 and perhaps higher polysulphuric acid. Some tetrasulphuric acid is also formed in the solvent self-dissociation. The conductivities and freezing points of solutions of some metal sulphates have been studied and the results are discussed. There is evidence that the HS2O7– and HS3O10– ions conduct by a proton-transfer process.