Determination of the strength of Ferrous Ammonium sulphate solution with the help of K2Cr2O7 solution

Introduction

This is a redox titration. In his reaction potassium dichromate acts as an oxidizing agent in acidic medium. It oxidize FAS (Fe2+) in Ferric sulphate (Fe3+). As the K2Cr2O7 is added in FAS initially green color appears due to formation of reduction product Cr2(SO4)3,(Cr3+) which on further addition of K2Cr2O7 change to purple color.

    The reactions involved are as follows:

  1. K2Cr2O7 + 4H2SO4 → K2SO4 + Cr2(SO4)3 + 4H2O + 3[O]

  2. 6FeSO4 + 3H2SO4 + 3[O] → 3Fe2(SO2)4 + 3 H2O

    The complete reaction is:

  1. 6[FeSO4 (NH4)2SO4.6H2O] + 7 H2SO4 + K2Cr2O7 → 3Fe2(SO4)3 + 6(NH4)2SO4 + Cr2(SO4) + K2SO4 + 4H2O