Answer:
Ans. Preparation of K2Cr2O7.
It involves three steps:
(i)Conversion of
chromite ore into the sod. chromate. Ore is powdered and fused with 
in the presence of
air when sodium chromate is formed.
2FeO.Cr2O3
+ 
O2
Fe2O3 + 2Cr2O3
Chromite ore
Cr2O3
+ 2Na2 CO3 + 
2Na2CrO4
+ 2CO2
Sod. chromate
(ii) Conversion of
sodium chromate into sodium dichromate. Sodium chromate is acidified with 
to give sodium
dichromate.
2Na2CrO4
+ H2SO4
Na2Cr2O7
Sodium dichromate
+Na2SO4
+ H2O
(iii)Conversion of
sodium dichromate into potassium dichromate.
Sodium dichromate
is treated with KCI and the resulting solution is evaporated to get orange
coloured crystals of potassium dichromate.
Na2Cr2O7
+ 2KCI K2Cr2O7
+ 2NaCl
Effect of pH. On increasing the
pH of K2Cr2O7 solution, the dichromate ion
changes to chromate ion.
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