Question

How is sodium chromate converted into sodium dichromate in the manufacture of potassium dichromate from chromite ore?
A. By the action of concentrated sulphuric acid
B. By roasting with soda ash
C. By the action of sodium hydroxide
D. By the action of limestone

Answer 1

Correct Answer - A
By the action of concentrated sulphuric acid, sodium chromate gets converted into sodium dichromate in the manufacture of potassium dichromate.
Various steps involved are:
Step I Concentration of the chromite ore by Wilfley method.
Step II Conversion of the concentrated chromite ore into `Na_2Cro_4`. Concentrated chromite ore is fused with molten `Na_2CO_3` in the presence of air when `Na_2CrO_4` and `Fe_2O_3` are formed.
Step III Conversion of `Na_2CrO_4` into `Na_2Cr_2O_7`.
Aqueous solution of `Na_2CrO_4` is acidified to `Na_2Cr_2O_7`
`Na_2CrO_4+H_2underset("Dil")SO_4toNa_2Cr_2O_7+H_2O`