3H S 2MnO + 3S + 2OH + 2H O (ii) It oxidises thiosulphate into sulphate 8MnO + 3S O + H O 6SO + 8MnO + 2OH Figure . Structure of permanganate ion XII U4-D-Block-Jerald XII U4-D-Block-Jerald - - - - b) In alkaline medium: In the presence of alkali metal hydroxides, the permanganate ion is converted into manganate. MnO + e MnO This manganate is further reduced to MnO by some reducing agents. MnO + 2H O + 2e MnO + 4OH − So the overall reaction can be written as follows.
MnO + 2H O + 3e MnO + 4OH This reaction is similar as that for neutral medium. Baeyer’s reagent: Cold dilute alkaline KMnO is known as Baeyer’s reagent. It is used to oxidise alkenes into diols. For example, ethylene can be converted into ethylene glycol and this reaction is used as a test for unsaturation.
c) In acid medium: In the presence of dilute sulphuric acid, potassium permanganate acts as a very strong oxidising agent. Permanganate ion is converted into Mn + ion. MnO + 8H + 5e Mn + 4H O + − → The oxidising nature of potassium permanganate (permanganate ion) in acid medium is illustrated in the following examples. (i) It oxidises ferrous salts to ferric salts.
2MnO + 10Fe + 16H 2Mn + 10Fe + 8H O + + + + → (ii) It oxidises iodide ions to iodine 2MnO + I + 16H 2Mn + 5I + 8H O + + → (iii) It oxidises oxalic acid to CO 2MnO + COO + 16H 2Mn + 10CO + 8H O + (iv) It oxidises sulphide ion to sulphur 2MnO + S + 16H 2Mn + S + 8H O + + → (v) It oxidises nitrites to nitrates 2MnO + 5NO + 6H 2Mn + 5NO + 3H O + (vi) It oxidises alcohols to aldehydes. 2KMnO + 3H SO + CH CH OH K SO + 2MnSO + 5CH CHO + 8H O (vii) It