Saved Bookmarks
| 1. |
How is potassium permanganate prepared from pyrolusite? OR Write the preparation of KMnP_(4). |
|
Answer» Solution :Pottassium permanganate, `KMnO_(4)` is prepared from pyrolusite ore. `MnO_(2)` by following steps: When pyrolusite aore `(MnO_(2))` is fused with alkali metal hhdroxide (`KOH` or `K_(2)CO_(3)`) in the presence of an oxidising agentlike `KNO_(3)` or `KClO_(3)` in air, a green coloured potassium manganate `K_(2)MnO_(4)` is obtained. (i) `2MnO_(2)+4KOH+O_(2) to 2K_(2)MnO_(4)+2H_(2)O` (ii) `2MnO_(2)+2K_(2)CO_(3)+O_(2) to 2K_(2)MnO_(4)+2CO_(2)` (iii) `MnO_(2)+2KOH+KNO_(3) to K_(2)MnO_(4)+KNO_(2)+H_(2)O` (iv) `3MnO_(2)+6KOH+KClO_(3)to3K_(2)MnO_(4)+KCl+3H_(2)O` The fused `K_(2)MnO_(4)` is oxidised to `KMnO_(4)` is carrid out by `H_(2)SO_(4)` or by passing `CO_(2)` or `Cl_(2)` or`O_(3)` through the solution. `3K_(2)MnO_(4)+2H_(2)SO_(4)to2K_(2)SO_(4)+2KMnO_(4)+2H_(2)O+MnO_(2)` `3K_(2)MNO_(4)+4CO_(2)+2H_(2)Oto2KMnO_(4)+MnO_(4)+4KHCO_(3)` `2K_(2)MnO_(4)+Cl_(2)to2KMnO_(4)+2KCl` `2K_(2)MnO_(4)+H_(2)O+O_(3)to2KMnO_(4)+2KOH+O_(2)` (b) By electrolytic oxidation:k The aqueous of `K_(2)MnO_(4)` is electrolysed between iron electrodes SEPARATED by a diaphragm, so that manganate ion `MnO_(4)^(2-) undergoes oxidation at anode forming permanganate ion `MnO_(4)` At anode: `underset("Green")(MnO_(4)^(2-)to underset("PURPLE")(MnO_(4)^(-))+e^(-)` At CATHODE: `2H^(+)+2e^(-)toH_(2(g))` During ELECTROLYSIS, `OH^(-)` are oxidised at anode liberating oxygen `(O_(2))` which also oxidises `MnO_(4)^(2-)` to `MnO_(4)^(-)`. `2OH^(-)toH_(2)O+[O]+2e^(-)` `2K_(2)MnO_(4)+H_(2)O+[O]to2KMnO_(4)+2KOH` Finally, the electrolytic solution is filtered and evaporated to obtained deep purple BLACK crystals of `KMnO_(4)`. |
|