Grade 12th passPhysical Chemistry
urgent plz....why titration of K2Cr2O7 is done using Mohr salt but not only ferrous sulphate..
urgent plz....
why titration of K2Cr2O7 is done using Mohr salt but not only ferrous sulphate..
1 Answer
Aarti Gupta
Mohr’s salt which is Ferrous ammonium sulphate [FeSO4(NH4)2SO4.6H2O] is a stable double salt in which FeSO4 being its active constituent. Acidic potassium dichromate,K2Cr2O7 solution is a strong oxidizing agent which is rapidly reduced by ferrous ion at the ordinary temperature to a green chromic salt when added to ferrous ammonium sulphate or Mohr’s salt solution containing dilute H2SO4.In this reaction ferrous sulphate is oxidized to ferric sulphate while ammonium sulphate remains unreacted.
Indicator used not oxidized as long as Fe2+ ions are there in the solution. The slight excess amount of dichromate will oxidize the indicator when all of the Fe2+ ions have been converted to Fe3+ ions resulting in colour change of the solution from greenish (due to Cr3+) to purple.Change in colour helps in determining the end-point.So Mohr’s salt is used in titration of potassium dichromate.
Indicator used not oxidized as long as Fe2+ ions are there in the solution. The slight excess amount of dichromate will oxidize the indicator when all of the Fe2+ ions have been converted to Fe3+ ions resulting in colour change of the solution from greenish (due to Cr3+) to purple.Change in colour helps in determining the end-point.So Mohr’s salt is used in titration of potassium dichromate.
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