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.