describe the preparation of k2cr2o7 from chromite ore and explain the reaction of k2cr2o7 with acid FeSo4 , KI and H2S ?

K2Cr2O7 is prepared from the chromate or ferrochrome ore whose molecular formula is  FeO.Cr2O3. The steps involved are as follows:

(a) Preparation of sodium chromate

  4FeO.Cr2O3 + O2    Fe2O3 + 4Cr2O3

  4Na2CO3 + 2Cr2O3 + 3O2     4Na2CrO4 + 4CO2

(b) Conversion of sodium chromate into sodium dichromate.

  2Na2CrO4 + H2SO4    Na2Cr2O7 + Na2SO4 + H2O

(c) Conversion of sodium dichromate into potassium dichromate.

  Na2Cr2O7 + 2KCl    K2Cr2O7 + 2NaCl

Chemical properties:

  1. -  Reaction with Acidic FeSO4: Ferric sulphate is formed

  K2Cr2O7 + 7H2SO4 + 6FeSO4    K2SO4 + Cr2(SO4)3 + 3Fe2(SO4)3 + 2H2O

 

  1. -  Reaction with KI: Iodine is released

  K2Cr2O7 + 7H2SO4 + 6Kl    4K2SO4 + Cr2(SO4)3 + 3l2 + 7H2O

 

  1. -  Reaction with H2S: Sulphur is formed.

  K2Cr2O7 + 4H2SO4 + 3H2S    K2SO4 + Cr2(SO4)3 + 7H2O + 3S

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