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Give chemical reactions showing oxidizing character of KMnO_(4) |
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Answer» Solution :`KMnO_(4)` act as strong OXIDIZING AGENT in neutral, alkaline and in acidic medium. (a) Oxidizing action in neutral or weak alkaline medium: (i) Oxidation of iodide to iodate `2MnO_(4)^(-) + H_(2)O + I^(-) rarr 2MnO_(2)+ 2OH^(-) + IO_(3)^(-)` (ii) Thiosulphate is oxidized almost quantitatively to sulphate `8MnO_(4)^(-) + 3S_(2)O_(3)^(2-) + H_(2)O rarr 8MnO_(2) + 6SO_(4)^(2-) + 2HO^(-)` (iii) Manganous salt is oxidized to `MnO_(2)`. The reaction is catalysed by ZnO or `ZnSO_(4)`. `2MnO_(4)^(-) + 3Mn^(2+) + 2H_(2)O overset(ZnO)rarr 5MnO_(2) + 4H^(+)` (b) Oxidizing action is acidic medium: (i) Iodine is liberated from potassium iodide `10I^(-) + 2MnO_(4)^(-) + 16H^(+) rarr 2Mn^(2+) + 8H_(2)O 5I_(2)` (ii) `Fe^(2+)` ion (green) is converted to `Fe^(3+)` (yellow) `5Fe^(2+) + MnO_(4)^(-) + 8H^(+) rarr Mn^(2+) + 4H_(2)O + 5Fe^(3+)` (iii) Oxalate ion or OXALIC ACID is oxidized at 333K `5C_(2)O_(4)^(2-) + 2MnO_(4)^(-) + 16H^(+) rarr 2Mn^(2+) + 8H_(2)O + 10CO_(2)` (iv) Hydrogen sulphide is oxidized sulphur is precipitated `H_(2)S rarr 2H^(+) + S^(2-)` `5S^(2-) + 2MnO_(4)^(-) + 16H^(+) rarr 2Mn^(2+) + 5S + 8H_(2)O` (v) Sulphurous acid or sulphite is oxidized to a sulphate or sulphuric acid. `5SO_(3)^(2-) + 2MnO_(4)^(-) + 6H^(+) rarr 2Mn^(2+) + 3H_(2)O + 5SO_(4)^(2-)` (vi) NITRITE is oxidized to nitrate `5NO_(2)^(-) + 2MnO_(4)^(-) + 6H^(+) rarr 2Mn^(2+) + 5NO_(3)^(-) + 3H_(2)O` In permanganate titrations, the HCl is not used because hydrochloric acid is oxidized to chlorine `(Cl_(2)) " by" MnO_(4)^(-)` |
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