Question

Preparation and chemical reaction of k2,cr2,o7 and kmno4

Answer 1

Engineering Entrance ExamsJEE MainChemistryArticle

Prepration, Properties and Uses of K2Cr2O7 and KMnO4

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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, KMnO4 decomposes to potassium manganate and oxygen.



Potassium Dichromate

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

1. Preparation of Sodium Chromate

Chromite ore is finely powdered and is heated with sodium carbonate in the presence of air in a reverberatory furnace. This reaction produces sodium chromate.



2. Conversion of sodium chromate into sodium dichromate

The sodium chromate formed in the above reaction is treated with concentrated sulphuric acid to form sodium dichromate.



Sodium sulphate, on cooling, separates as Na2SO4.10H2O leaving sodium dichromate.

3. Conversion of Sodium dichromate into potassium dichromate

The sodium dichromate formed above is treated with KCl to form potassium dichromate.



Properties

K2Cr2O7 is soluble in not water.It is in the form of orange crystals.On heating potassium dichromate decomposes and forms potassium chromate and chromic oxide.
It is used in industries as an oxidizing agent.