Answer :

(i) the chromite ore (FeCr2O4) is fused with sodium hydroxide (NaOH)

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

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