NEET-XII-Chemistry
08: The d-and f-Block Elements
- #14Describe the preparation of potassium dichromate from iron chromite ore.
What is the effect of increasing pH on a solution of potassium dichromate?
Ans : Potassium dichromate is prepared from chromite ore
in the 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 dichromate being less soluble than sodium chloride is obtained in the form of orange coloured crystals and can be removed by filtration.
The dichromate ion
exists in equilibrium with chromate 
ion at pH 4. However, by changing the pH, they can be interconverted.
2CrO42-→Acid2HCrO4-→Acid2Cr2O72-Cr2O72-→Base2HCrO42-→Base2CrO42-