Give the preparation of Potassium dichromate ,`K_2Cr_2O_7`.

Explanation

(i) Conversion of chromite ore into Sodium chromate.
`underset("Chromiteore")(4FeCr_2O_4) + 16NaOH + underset((Ar))(7O_2) to underset("Sodium chromate")(8Na_2 CrO_4) + 2Fe_2O_3 + 8H_2O`
(ii) Conversion of Sodium Chromate into Sodium dichromate
`underset("Sodium Chromate")(2Na_2CrO_4) + H_2SO_4 to underset("Sodiumdicromate")(Na_2Cr_2O_7) + Na_2SO_4 + H_2O`
(iii) Conversion of Sodium dichromate into Potassium dichromate
`underset("Sodiumdichromate")(Na_2Cr_2O_7) + 2KCl to underset("Potassiumdichromate")(K_2Cr_2O_7) + 2NaCl`