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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 · 2024 · Paper I

Q8(d). Colour centres in sodium chloride

Question

Why is yellow colour observed when sodium chloride is heated in sodium vapour?

Answer in brief

Sodium-rich conditions create electron-occupied chloride vacancies, called F centres. Their electronic absorption removes part of the visible light, giving the crystal a yellow colour.

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CoversF centrecolour centremetal excess defectNaCl heated in sodium vapournon-stoichiometric defects

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