Indicate the steps in the preparation of:
(i) K2Cr2O7from chromite ore.
(ii) KMnO4from pyrolusite ore.
Indicate the steps in the preparation of:
(i) K2Cr2O7from chromite ore.
(ii) KMnO4from pyrolusite ore.
(i)
Potassium dichromate (
)is prepared from chromite ore 
inthe following steps.
Step (1):Preparation of sodium chromate
Step (2):Conversion of sodium chromate into sodium dichromate
Step(3):Conversion of sodium dichromate to potassium dichromate
Potassium chloride being less soluble than sodium chloride isobtained in the form of orange coloured crystals and can be removedby filtration.
The dichromate ion 
existsin equilibrium with chromate 
ionat pH 4. However, by changing the pH, they can be interconverted.
(ii)
Potassium permanganate (
)can be prepared from pyrolusite (MnO2).The ore is fused with KOH in the presence of either atmosphericoxygen or an oxidising agent, such as KNO3or KClO4,to give K2MnO4.
The green mass can be extracted with water and then oxidized eitherelectrolytically or by passing chlorine/ozone into the solution.
Electrolytic oxidation
At anode, manganate ions are oxidized to permanganate ions.
Oxidation by chlorine
Oxidation by ozone
(i)
Potassium dichromate ()is prepared from chromite ore inthe following steps.
Step (1):Preparation of sodium chromate
Step (2):Conversion of sodium chromate into sodium dichromate
Step(3):Conversion of sodium dichromate to potassium dichromate
Potassium chloride being less soluble than sodium chloride isobtained in the form of orange coloured crystals and can be removedby filtration.
The dichromate ion existsin equilibrium with chromate ionat pH 4. However, by changing the pH, they can be interconverted.
(ii)
Potassium permanganate ()can be prepared from pyrolusite (MnO2).The ore is fused with KOH in the presence of either atmosphericoxygen or an oxidising agent, such as KNO3or KClO4,to give K2MnO4.
The green mass can be extracted with water and then oxidized eitherelectrolytically or by passing chlorine/ozone into the solution.
Electrolytic oxidation
At anode, manganate ions are oxidized to permanganate ions.
Oxidation by chlorine
Oxidation by ozone
