Explain the method of preparation of sodium dichromate from chromite ore . Give the equation representing oxidation of ferrous salts by dichromate ion.

Explanation

Potassium dischromate is prepared from chromite are `FeCr_2O4` in the following steps.
Step : 1 : Preparation of sodium chromate
`4FeCr_O_4+16NaOH +7O_2 rarr 8 NaCrO_4+2 Fe_2O_3+8H_2O`
Step :2: Conversion of sodium chromate into sodium dichromate
`2Na_2CrO_4+Conc.H_2SO_4rarr Na_2Cr_2O_7+Na_2SO_4+H_2 O`
Oxidation of ferrous slats by dichromate ion
`Cr_2O_7^(2-)+6Fe^(3+)+7H_2O`