Question

write the preparation of sodium dichromate from ore(FeCr2O4).​

Answer 1

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Answer 2

Potassium dichromate is prepared from chromite ore (FeCr2O4) in the following steps.

Step (1):

Preparation of sodium chromate

4FeCr2O4 + 16NaOH + 7O2 → 8NaCrO4 + 2Fe2O3 + 8H2O

Step (2):

Conversion of sodium chromate into sodium dichromate

2Na2CrO4 + conc.H2SO4 → Na2Cr2O7 + Na2SO4 + H2O

Step(3): Conversion of sodium dichromate to potassium dichromate

Na2Cr2O7 + 2KCl → K2Cr2O7 + 2NaCl

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 (Cr2O2-7) ion exists in equilibrium with chromate (CrO2-4) ion at pH 4. However, by changing the pH, they can be interconverted.