question_answer 26)

 Describe the preparation of potassium permanganate. How does the acidified permanganate solution reacts with : (i) iron (ii) ions (iii) SO2 (iv) oxalic acid ? Write the ionic equations for the reactions.

Answer:

(i) Conversion of pyrolusite ore into potassiummanganate. Ore is fused with K2CO3 or KOH in the presence of oxidising agent KNO3 or KCIO3 to get K2MnIO4. (ii)Conversion of potassium managanate to potassium permanganate. Potassium manganate solution is electrolysed in a tank having nickel anode and iron cathode. Manganate ion is oxidised to give permanganate ion.         At cathode:        H+ + e?H H + H H2O              At anode:            Reactions: (a) Iron (II) ions MnO4? + 5Fe2+ + 8H+ Mn2+ + 5Fe3+ + 4H2O (b) SO2 2MnO4? + 5SO2 + 2H2O   2Mn2+ +  +4H+ (c) Oxalic acid + 10CO2 + 8H2O