Describe the preparation of potassium permanganate. How does the acidifiedpermanganate solution react with (i) iron(II) ions (ii) SO2and (iii) oxalic acid? Write the ionic equations for the reactions.
Describe the preparation of potassium permanganate. How does the acidifiedpermanganate solution react with (i) iron(II) ions (ii) SO2and (iii) oxalic acid? Write the ionic equations for the reactions.
Solution and Explanation
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.
2MnO2+4KOH+O2 \(\underrightarrow{-heat}\) 2K2MnO4 +2H2O
(Green)
The green mass can be extracted with water and then oxidized either electrolytically or by passing chlorine/ozone into the solution. Electrolytic oxidation
K2MnO4\(\leftrightarrow\)2K++\(MnO^{2-}_4\)
H2O\(\leftrightarrow\)H++OH-
At anode, manganate ions are oxidized to permanganate ions
\(MnO^{2-}_4\) \(\leftrightarrow\) \(MnO^{-}_4\)+e-
Green Purple
Oxidation by chlorine
2K2MnO4+Cl2 \(\rightarrow\) 2KMnO4+2KCl
2MnO4-+Cl2 \(\rightarrow\) 2\(MnO^{-}_4\)+2Cl-
Oxidation by ozone
2K2MnO4+O3+H2O \(\rightarrow\) 2KMnO4+2KOH+O2
2\(MnO^{2-}_4\)+O3+H2O \(\rightarrow\) 2\(MnO^{2-}_4\)+2OH-+O2
(i) Acidified KMnO4 solution oxidizes Fe (II) ions to Fe (III) ions i.e., ferrous ions to ferric ions
\(MnO^{-}_4\)+8H++5e-\(\rightarrow\) Mn2++4H2O
Fe2+\(\rightarrow\) Fe3++e-] x 5
\(MnO^{-}_4\)+5Fe2++8H+\(\rightarrow\) Mn2++5Fe3++4H2O
(ii) Acidified potassium permanganate oxidizes SO2 to sulphuric acid.
\(MnO^{-}_4\)+6H++5e-\(\rightarrow\) Mn2++3H2O] x 2
2H2O+2SO2+O2\(\rightarrow\) 4H++\(2So^{2-}_4\)+2e-] x 5
2\(MnO^{-}_4\)+10SO2+5O2+4H2O \(\rightarrow\) 2Mn2++\(10So^{2-}_4\)+8H+
(iii) Acidified potassium permanganate oxidizes oxalic acid to carbon dioxide.
\(MnO^{-}_4\)+8H++5e-\(\rightarrow\) Mn2++4H2O] x 2
\(C_2O^{2-}_4\)\(\rightarrow\) 2CO2+2e-] x 5
2MnO4+\(5C_2O^{2-}_4\)+16H+\(\rightarrow\) 2Mn2++10CO2+8H2O
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Concepts Used:
D and F Block Elements
The d-block elements are placed in groups 3-12 and F-block elements with 4f and 5f orbital filled progressively. The general electronic configuration of d block elements and f- block elements are (n-1) d 1-10 ns 1-2 and (n-2) f 1-14 (n-1) d1 ns2 respectively. They are commonly known as transition elements because they exhibit multiple oxidation states because of the d-d transition which is possible by the availability of vacant d orbitals in these elements.
They have variable Oxidation States as well as are good catalysts because they provide a large surface area for the absorption of reaction. They show variable oxidation states to form intermediate with reactants easily. They are mostly lanthanoids and show lanthanoid contraction. Since differentiating electrons enter in an anti-penultimate f subshell. Therefore, these elements are also called inner transition elements.
Read More: The d and f block elements