Write chemical reaction for preparation of K2Cr207 from chromite ore.

Explanation

The steps leading to the formation of `K_2Cr_2O_7` from `FeCr_2O_4` are as follows:
Step 1 : Chromite ore is powdered, mixed with sodium carbonate and quick lime and then roasted. Sodium chromate is produced with `CO_2` gas as :
`4FeCr_2O_4 + 8Na_2 CO_3 + 7O_2 to 8Na_2 CrO_4 + 2Fe_2O_3 + 8CO_2`
Products obtained in above reaction are extracted with water. `Na_2CrO_4 ` dissolves in water.
Step II : Sodium chromate solution is filtered and treated with concentrated `H_2SO_4` . The formation of sodium dichromate takes place as :
`2Na_2 CrO_4 + H_2SO_4 to Na_2Cr_2O_7 + Na_2SO_4 + H_2O`
`Na_2SO_4` crystallizes and is removed and clear solution is evaporated. Red crystals of sodium dichromate are obtained on cooling.
Step III : Sodium dichromate solution is treated with potassium chloride which gives potassium dichromate as : `Na_2Cr_2O_7 + 2KCl to K_2Cr_2O_7 + 2NaCl`