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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

Q5(a). Solubility of alkali-metal halides

Question

Explain why LiF is less soluble than LiI in water. Using your explanation, state, between CsF and CsI, which one would be more soluble in water.

Answer in brief

LiF is less soluble because its exceptionally strong lattice offsets hydration. For the large Cs⁺ ion, fluoride hydration becomes decisive and CsF is more soluble than CsI.

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Topic notes: ionic bonding: lattice energy, the Born–Haber cycle, Born–Landé and Kapustinskii equations and Fajans’ rules, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverslattice energyhydration energysolubility of alkali halidesLiF vs LiICsF vs CsI

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