Describe properties of potassium permanganate., Chemistry

Potassium permanganate is prepared from pyrolusite (MnO2). Pyrolusite is fused with KOH in the presence of atmospheric oxygen or an oxidising agent like potassium nitrate or potassium chlorate to give potassium manganate, K2MnO4.
1766_potassium permangnate.png 

The green mass is taken out with water and oxidized to potassium permanganate, electrolytically or by passing chlorine or ozone into solution.

Electrolytic oxidation
K2MnO4  2421_potassium permangnate1.png  2K+ + MnO42-
H2O  2421_potassium permangnate1.png  H+ + OH

During electrolysis manganate ions are oxidized to permanganate at anode

1781_potassium permangnate2.png 

At cathode hydrogen gas is liberated
2H2O + 2e-  702_potassium permangnate3.png  H2 + 2OH-

Oxidation by chlorine
2K2MnO4 + Cl2  702_potassium permangnate3.png  2KMnO4 + 2KCl
Or, 2MnO42- + Cl2  702_potassium permangnate3.png  2MnO4- + 2Cl

Oxidation by ozone
2K2MnO4 + O3 + H2O  702_potassium permangnate3.png  2KMnO4 + 2KOH + O2
Or, 2MnO42- + O3 + H2O  702_potassium permangnate3.png  2MnO42- + 2OH- + O

As a result of oxidation, the green colour of solution changes into purple. The purple solution containing KMnO4 is concentrated by evaporation which on cooling gives crystals of KMnO4.

The manganate (MnO42-) and permanganate (MnO2-) ions are tetrahedral in shape. The manganate is paramagnetic with one unpaired electron but the permanganate is diamagnetic.

The π-bonding takes place by overlie of p-orbitals of oxygen with d-orbitals of manganese. 


Potassium permanganate is violet crystalline solid having m.p. 523 K. it is soluble in water and its aqueous solution is purple in colour.
Result of heat: on heating, potassium permanganate changes into manganate and oxygen gas is evolved.
2KMnO4  702_potassium permangnate3.png  K2MnO4 + MnO2 + O2
Effect of alkalies: on heating with alkalies, potassium permanganate converts into manganate and oxygen gas is evolved.
4KMnO4 + 4KOH  702_potassium permangnate3.png  4K2MnO4 + 2H2O + O2
Oxidising properties: KMnO4 acts as a very powerful oxidising agent in acidic, neutral and alkaline media. The equations representing oxidation in these media are given below:

In acidic medium
2KMnO4 + 3H2SO4  702_potassium permangnate3.png  K2SO4 + 2MnSO4 + 3H2O + 5[O]
Or, MnO4- + 8H+ + 5e-  702_potassium permangnate3.png  Mn2+ + 4H2O [
1608_potassium permangnate4.png  = + 1.52 V]

In neutral or alkaline medium
2KMnO4 + H2O  702_potassium permangnate3.png  2KOH + 2MnO2 + 3[O]
Or, MnO4- + 2H2O + 3e-  702_potassium permangnate3.png  MnO2 + 4OH- [
1608_potassium permangnate4.png  = + 1.23 V]







Posted Date: 6/25/2012 8:38:01 AM | Location : United States

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