Peroxodisulfate ion, s2o82−, oxidizes iron(ii) ion to iron(iii) ion in aqueous solution and is itself reduced to sulfate ion. write a balanced equation.

The balanced equation for the reaction is;
2Fe2+(aq) + S2O8^2-(aq)  = 2SO4^2-(aq) + 2Fe3+(aq)
 This reaction occurs during the reaction of peroxodisulfate ions and iodide ions in aqueous form to form sulfate ions and iodine, where iron ii ions or iron iii ions acts as a catalyst.
Iron II ions is oxidized to iron III ions while peroxodisulfate(VI) is reduced to sulfate (VI) ions.

They can measure  the amount of energy gained or lost