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Describe the preparation of potassium permanganate from pyrolusite ore by electrochemical method. Discuss its important properties and uses. |
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Answer» Solution :Preparation of potassium permanganate. `KMnO_(4)` is PREPARED on a large scale from PYROLUSITE. It is fused with KOH in the presence of air forming a green mass of potassium manganate. `2MnO_(2) + 4KOH + O_(2) to underset("Pot. manganate")(2K_(2)Mnoverset(Delta)O_(4))+ 2H_(2)O` Potassium manganate is oxidised electrochemically to permanganate ion in the cathode compartment. At anode : `MnO_(4)^(2-) to MnO_(4)^(-)+ e^(-)` At cathode : `2H^(+)+ 2e^(-) to 2H` `2H to H_(2)` Properties. The important properties of `KMnO_(4)` are discussed below : 1. It is a dark violet crystalline solid having a metallic lustre 2. Its melting point is 523 K. 3. It is slightly soluble in water. 4. When heated strongly, it decomposes to give oxygen `2KMnO_(4) to K_(2)MnO_(4)+ MnO_(2)+ O_(2)` 5. Oxidising character. Potassium permanganate acts as a powerful oxidising agent in neutral, alkaline or acidic solution because it liberales nascent oxygen as Neutral solution, `2KmnO_(4) +H_(2)O to 2KOH+ 2MnO_(2)+ 3O` or `MnO_(4)^(-)+ 2H_(2)O+ 3e^(-) to MnO_(2)+ 4OH^(-)` Alkaline solution ` 2KmnO_(4)+2KOH to 2K_(2)MnO_(4)+ H_(2)O+O` or `MNO_(4)^(-)+ e^(-) to MNO_(4)^(2-)` Acidic solution `2KmnO_(4)+ 3H_(2)SO_(4) to K_(2)SO_(4) + 2MnSO_(4)+ 3H_(2)O+ 5O` or `MnO_(4)^(-)+ 8H^(+)+ 5e^(-) to Mn^(2+)+ 4H_(2)O` However, it is frequently used in acidic medium in the laboratory. The important oxidation reactions of acidified KMnO4 in the laboratory are :However, it is frequently used in acidic medium in the laboratory. The important oxidation reactions of acidified KMnO4 in the laboratory are : (i) It oxidises ferrous salts to ferric salis. `2FeSO_(4) + H_2SO_4 +O toFe_(2) (SO_(4))_(3) + H_(2)O` or `5Fe^(2+)+ MnO_(4)^(-) + 8H^(+) to Mn^(2+) + 4H_(2)O+ 5Fe^(3+)` (ii) It oxidises oxalates or oxulic acid to carbon dioxide `underset(COOH)underset(|)COOH+O overset(50-60^(@)C)to 2CO_(2)+ H_(2)O` `underset(COO)underset(|)COO+ 2MNO_(4)^(-)+ 16H^(+)overset(50-60^(@)C)to 2MN^(2+)+ 8H_(2)O+ 10CO_(2)` (iii) It oxidises potassium iodide to iodine. `2KI+H_(2)O+O to 2KOH+I_(2)` or `10I^(-)+ 2MNO_(4)^(-)+ 16H^(+) to 2MN^(2+)+ 8H_(2)O+ 5I_(2)` (iv) oxidises sulphur dioxide to sulphuric acid. `SO_(2)+ O + H_(2)O to H_(2)SO_(4)` `5SO_(2)+ 2MnO_(4)^(-)+ 2H_(2)O to 2Mn^(2+) + 5SO_(4)^(2-)+4H^(+)` Uses of `KMnO_(4)`. It is used: (i) as an oxidising agent in the laboratory and in industry. (ii) as a disinfectant, germicide and deodorant. (iii) in qualitative and quantitative analysis. (iv) as alkaline solution in organic reactions under the NAME Baeyer.s reagent. (v) for purification of water. |
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