Similar experiments may be made with ferrous sulphate against permanganate.
The oxidation of ferro-ion, or of iodide-ion, may be represented, most simply, by the equations:
2 Mn7+ + 10 Fe2+ → 2 Mn2+ + 10 Fe3+
and
2 Mn7+ + 10 I− → 2 Mn2+ + 5 I2.
Each heptavalent manganese ion is derived from a salt, such as MnX′7 or Mn2Y″7, and, consequently, when two manganese ions Mn7+ are reduced, ten univalent negative ions X′, or five bivalent ions Y″, are liberated and become available for salt formation with the ferric ions, produced, or with the hydrogen ions (from hydroiodic acid) set free by the oxidation of the iodide ions to iodine.
Thus, the oxidation of ferrous sulphate by permanganate, in the presence of sulphuric acid, may be represented, in greater detail, by the equations:
2 KMnO4 + H2SO4 ⇄ K2SO4 + 2 HMnO4
(1)
2 HMnO4 + 7 H2SO4 ⇄ Mn2(SO4)7 + 8 H2O