The formula for Caro's acid is H2SO5.Structure of Caro's acid
Oxidation number of sulphur in H2SO5 is : x+3 (oxygen) +2 (oxygen in peroxide bond)+ 2(hydrogen) = 0 x+3(−2)+2(−1)+2(1)=0 x−6−2+2=0 x=+6 The formula of Marshall's acid is H2S2O8.
Oxidation number of sulphur in H2S2O8 is : 2x+6 (oxygen) +2 (oxygen in peroxide bond)+2(hydrogen)=0 2x+6(−2)+2(−1)+2(1)=0 2x−12+(−2)+2=0 2x=12⇒x=+6 ∴ Oxidation numbers of sulphur in Caro's acid and Marshall's acid are +6 and +6 respectively.