Dichromates are generally prepared from chromate, which in turn are
obtained by the fusion of chromite ore (FeCr2O4) with sodium or
potassium carbonate in free access of air The reaction with sodium
carbonate occurs as follows:
4 FeCr2O4 + 8 Na2CO3 + 7 O2 ® 8 Na2CrO4 + 2 Fe2O3 + 8 CO2
The yellow solution of sodium chromate is filtered and acidified
with sulphuric acid to give a solution from which orange sodium
dichromate, Na2Cr2O7 2H2O can be crystallised 2Na2CrO4 + 2 H
+ ® Na2Cr2O7 + 2 Na
+ + H2O
Rationalised 2023-24
106
Chemistry
Sodium dichromate is more soluble than potassium dichromate