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Indian Forest Service (Mains)

Chemistry optional

  • 2 papers
  • 200 marks each
  • 3 h per paper

Paper I covers physical and inorganic chemistry.

Indian Forest Service (Mains), Chemistry optional · 2022 · Paper I

Q5(c). Oxidation of cobalt ammine

Question

Explain why [Co(H₂O)₆]²⁺ is stable but [Co(NH₃)₆]²⁺ is readily oxidized to [Co(NH₃)₆]³⁺ in air.

Answer in brief

Ammonia stabilises Co(III) much more strongly relative to Co(II) than water does, lowering the Co(III)/Co(II) potential and making oxidation of the Co(II) ammine by oxygen favourable.

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Topic notes: Werner theory, isomerism, IUPAC names and valence bond theory of complexes, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverscobalt ammine complexesCo(II) to Co(III) oxidationCFSE low-spin d6reduction potentialstability constants

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