Oxidation number of S in H2S2O8
(Peroxidisulphuric acid or Marshall’s acid)
By usual method : H2S2O8
1 x 2 + 2a + 8 (-2) = 0
2a = + 16 - 2 = 14 or a = + 7
Similar to Caro’s acid, Marshall’s acid also has a peroxide linkage and S shows +6 oxidation state in it.
Therefore the evaluation of oxidation state of sulphur should be made as follows,
or 2 + 2a – 12 – 2 = 0 or a = + 6
