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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 · 2023 · Paper I

Q5(c). Normal and inverse spinels

Question

In a book, it is written that the structures of both Fe₃O₄ and Mn₃O₄ are normal spinel. With the help of CFSE, establish whether the structures written in the book are correct or not.

Answer in brief

The statement is incorrect for Fe₃O₄, which is inverse spinel, but correct in cation distribution for Mn₃O₄, a tetragonally distorted normal spinel.

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The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

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Topic notes: inorganic solids: perovskite, spinel, ReO₃, corundum, high-Tc superconductors and solid-state synthesis, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversnormal spinelinverse spinelCFSEFe₃O₄ magnetiteMn₃O₄ hausmanniteoctahedral site preference

All parts of Question 5