Indicate the steps in the preparation of: (i) K2Cr2O7 from chromite ore

4FeCr2O4 +16 NaOH+ 7O2 8Na2CrO4 +2Fe2O3 +8H2O 

The yellow solution of sodium chromate is then filtered and acidified with sulphuric acid giving its dichromate. 

2Na2CrO4 +H2SO4  Na2Cr2O7 + Na2SO4 +H2O 

On cooling, sodium sulphate crystallizes out as Na2SO4.10H2O and is removed. 

Na2Cr2O7 +2KCl  K2Cr2O7 + 2NaCl 

(ii) the pyrolusite ore(MnO2) is oxidised in the presence of potassium hydroxide by heating. 

2MnO2 + 4KOH +O2  2K2MnO4 + 2H2O 

The green potassium manganate (K2MnO4) is then treated with a current of chlorine or ozone to oxidise potassium manganate to potassium permanganate. 

2K2MnO4 +Cl2  2KCl +2KMnO4

K2MnO4 +O3 +H2O  2KMnO4 +2KOH +O2