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UPSC Combined Geo-Scientist

Chemist

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

Mains Paper I covers inorganic chemistry.

UPSC Combined Geo-Scientist, Mains · 2018 · Mains Paper I

Q1(a). Lithium hydride

Question

How lithium hydride can be prepared? Write the product of the reaction between lithium hydride and carbon dioxide. Whether it (LiH) is electrovalent or covalent compound? Explain.

Answer in brief

LiH is prepared by direct combination of lithium and hydrogen; reaction with CO₂ can give lithium formate. Solid LiH is predominantly ionic.

Key points

  • Heat lithium in dry hydrogen: 2Li + H₂ → 2LiH.
  • Under suitable elevated-temperature conditions, LiH + CO₂ → HCOOLi. Hydride adds to electrophilic carbon, producing formate.
  • LiH is a saline hydride containing Li⁺ and H⁻ in a rock-salt lattice. Its crystalline, nonvolatile character is consistent with predominantly electrovalent bonding.

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.

Model answer to Q1(a), 2018 Mains Paper I: solution pages 1 and 2
Solution pages 1 and 2 of 17
Read the whole 2018 solution2018 question paper

CoversLithium hydrides-block chemistry

All parts of Question 1