Question

write preparation of KMno4

Answer 1

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 KNO3or 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

K2MnO4   ↔    2K+   +    MnO2-4

H2O     ↔   H+   +  OH-

At anode, manganate ions are oxidized to permanganate ions.

MnO2-4       ↔     MnO-4    +   e-

Green                 Purple 

Oxidation by chlorine

Answer 2

Potassium Permanganate

It is prepared from the mineral pyrolusite (MnO2). The preparation involves following steps:

1. Conversion of MnO2 to potassium manganate

The powdered pyrolusite is fused with potassium hydroxide in presence of air to form potassium manganate, which is a green colored compound.


2. Oxidation of potassium manganate to potassium permanganate

Oxidation can be done in two methods. They are Chemical oxidation and Electrolytic oxidation.

Chemical Oxidation

In this method potassium manganate is treated with chlorine or ozone to form potassium permanganate.


Electrolytic Condition

In this method, potassium manganate solution is electrolyzed.



In this process, manganate ions are converted to permanganate.


After oxidation, the green color solution changes to a purple color solution which is concentrated by evaporation and forms crystals on cooling.

Properties

It is soluble in hot water.It is in the form of purple crystals.On heating, KMnO4decomposes to potassium manganate and oxygen.



Potassium Dichromate

It is prepared from chromite ore (FeCr2O4). This preparation involves many steps.