permanganate: Potassium manganate thus obtained can be oxidised in two ways , either by chemical oxidation or electrolytic oxidation. Chemical oxidation: In this method potassium manganate is treated with ozone (O ) or chlorine to get potassium permanganate. 2MnO + O + H O 2MnO + 2OH + O 2MnO + C l 2MnO + 2Cl Electrolytic oxidation In this method aqueous solution of potassium manganate is electrolyzed in the presence of little alkali. K MnO 2K + MnO H O H + OH ⇀ ↽ ⇀ ↽ − Manganate ions are converted into permanganate ions at anode.
Green purple MnO MnO e H is liberated at the cathode. 2H + 2e H − → ↑ The purple coloured solution is concentrated by evaporation and forms crystals of potassium permanganate on cooling. Physical properties: Potassium permanganate exists in the form of dark purple crystals which melts at K. It is sparingly soluble in cold water but, fairly soluble in hot water.
XII U4-D-Block-Jerald XII U4-D-Block-Jerald - - - - Structure of permanganate ion Permanganate ion has tetrahedral geometry in which the central Mn + is d s hybridised. Chemical properties: . Action of heat: When heated, potassium permanganate decomposes to form potassium manganate and manganese dioxide. 2KMnO K MnO + MnO + O .
Action of conc H SO On treating with cold conc H SO , it decomposes to form manganese heptoxide, which subsequently decomposes explosively. 2KMnO + 2H SO (cold) Mn O + 2KHSO + H O Mn O ∆ 4MnO + 3O But with hot conc H SO , potassium permanganate give MnSO 4KMnO + 6H SO (hot) 4MnSO + 2K SO + 6H O + 5O . Oxidising property: Potassium permanganate is a strong oxidising agent, its oxidising action differs in different reaction medium. a) In neutral medium: In neutral medium, it is reduced to MnO MnO + 2H O + 3e MnO + 4OH (i) It oxidises H S to sulphur 2MnO +