This experiment determines the ferrous iron (Fe2+) content of a Mohr's salt sample by redox titration against standard N/20 potassium dichromate (K2Cr2O7), a primary standard oxidant. The reaction follows Cr6+ to Cr3+ (gaining 6 electrons) and Fe2+ to Fe3+ (losing 1 electron) stoichiometry, and equivalent weight calculations reflect these electron transfers. A critical feature of this experiment is the use of an external indicator: potassium hexacyanoferrate(III) (K3[Fe(CN)6], freshly prepared) on a white spot plate. While Fe2+ is present in the titration flask, a sample drop transferred to the spot plate gives an immediate blue-green precipitate with K3[Fe(CN)6]. The end point is reached when the transferred drop produces no colour change — indicating all Fe2+ has been oxidised. K2Cr2O7 and all Cr(VI) compounds are classified as Group 1 IARC carcinogens, and all chromate-containing waste must be collected in labelled containers and never disposed of down the sink. The iron content is reported as g/L Fe2+ and g/L Mohr's salt.