Q. Describe Peroxomonosulphuric Acid?
It is also known as permonosulphuric acid. It is obtained by the action of chlorosulphuric
acid on cold anhydrous hydrogen peroxide :
H2O2 + ClSO2.OH --------------> H-O-O-SO2.OH +HCl
It may also be prepared by the action of concentrated sulphuric acid on 5% hydrogen peroxide:
H2O2 + H2SO4 --------------> H-O-O-SO2.OH + H2O
Peroxomonosulphuric acid may also be obtained by hydrolysis of peroxodisulphuric acid at 273 K or by grinding potassium peroxodisulphate crystals with sulphuric acid in a freezing mixture.
H2S2O8 + H2O-------------> H2SO5 + H2SO4
K2S2O8 + H2SO4---------> H2SO5 + K2S2O7
Peroxomonosulphuric acid is a white crystalline solid, m. p. 318 K. However, the salts of this acid are unstable in the solid state. The acid is a strong oxidising agent. It oxidises SO2 to SO3, sulphites to sulphates, ferrous salts to ferric salts and liberates iodine immediately from a solution of potassium iodide:
2KI + H2SO5-----------> K2SO4 + H2O + I2
2FeSO4 + H2SO5------------> Fe2 (SO4)3+ H2O