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Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with (i) iron(II) ions (ii) SO2 and (iii) oxalic acid? Write the ionic equations for the reactions. - Chemistry

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ConceptSome Important Compounds of Transition Elements - Oxides and Oxoanions of Metals

Question

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

Solution

Potassium permanganate can be prepared from pyrolusite (MnO2). The ore is fused with KOH in the presence of either atmospheric oxygen or an oxidising agent, such as KNO3 or KClO4, to give K2MnO4.

The green mass can be extracted with water and then oxidized either electrolytically or by passing chlorine/ozone into the solution.

Electrolytic oxidation

`K_2MnO_4 harr 2K^(+) + MnO_4^(2-)`

`H_2O harr H^(+) + OH^(-)`

At anode, manganate ions are oxidized to permanganate ions.

`MnO_4^(2-) harr MnO_4^(-) + e^(-)`

Green       Purple

Oxidation by chlorine

`2K_2MnO_4 + Cl_2 -> 2KMnO_4 + 2KCl`

`2MnO_4^(2-) + Cl_2 -> 2MnO_4^- + 2Cl^(-)`

Oxidation by ozone

`2K_2MnO_4 + O_3 + H_2O -> 2KMnO_4 + 2KOH +O_2`

`2MnO_4^(2-) + O_3+H_2O -> 2MnO_4^(2-) + 2OH^(-) + O_2`

(i) Acidified KMnO4 solution oxidizes Fe (II) ions to Fe (III) ions i.e., ferrous ions to ferric ions.

`MnO_4^(-) + 8H^(+) + 5e^(-) -> Mn^(2+) + 4H_2O`

                              `Fe^(2+) -> Fe^(3+) + e^(-)]xx5`

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`MnO_4^(-) + 5Fe^(2+)+8H^(+) -> Mn^(2+) + 5Fe^(3+) + 4H_2O`

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(ii) Acidified potassium permanganate oxidizes SOto sulphuric acid.

           `MnO_4^(-) + 6H^(+) + 5e^(-) -> Mn^(2+) + 3H_2O]xx2`

          `2H_2O+2SO_2+O_2 -> 4H^(+)+2SO_4^(2-)+2e^(-)]xx5`

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 `2MnO_4^(-)+10SO_2+5O_2+4H_2O->2Mn^(2+) + 10SO_4^(2-)+8H^(+)`

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(iii) Acidified potassium permanganate oxidizes oxalic acid to carbon dioxide.

`MnO_4^(-)+8H^(+) 5e^(-)  -> Mn^(2-) + 4H_2O]xx2`

                    `C_2O_4^(2-) -> 2CO_2+2e^(-)]xx5`

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`2MnO_4^(-) + 5C_2O_4^(2-)+16H^(+)-> 2Mn^(2+) + 10CO_2 + 8H_2O`

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 NCERT Solution for Chemistry Textbook for Class 12 (2018 to Current)
Chapter 8: The d-block and f-block Elements
Q: 16 | Page no. 235
Solution Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with (i) iron(II) ions (ii) SO2 and (iii) oxalic acid? Write the ionic equations for the reactions. Concept: Some Important Compounds of Transition Elements - Oxides and Oxoanions of Metals.
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