Marshalls acid is prepared by the electrolytic oxidation of H2SO4 as 2H2SO4→H2S2O8+2H⊕+2e−
Oxygen and hydrogen are byproducts. In such Electrolysis 2.24 L of H2 amd 0.56 L O2 were produced at STP. The weight of H2S2O8 formed is: