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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 · 2022 · Mains Paper I

Q1(a). Minerals and framework structures

Question

Match the following: (i) Mg₂SiO₄; (ii) Be₃Al₂Si₆O₈ (Beryl); (iii) Mqm+[Siₓ₋ᵧP₁₋ₓAl₁₋ᵧO₄]; (iv) MgAl₂O₄; (v) Ca(OH)(PO₄)₃. (A) Spinel; (B) Zeolite; (C) Orthosilicate; (D) Aluminophosphate; (E) Cyclosilicate; (F) Hydroxyapatite; (G) Intercalation Compound.

Answer in brief

Intended matches: (i)-C; (ii)-E; (iii)-D; (iv)-A; (v)-F.

Key points

  • Mg₂SiO₄ (forsterite) is an orthosilicate, containing isolated SiO₄⁴⁻ tetrahedra.
  • Beryl is a cyclosilicate with six-membered Si₆O₁₈ rings. Its correct formula is Be₃Al₂Si₆O₁₈; the printed O₈ is a misprint.
  • The mixed Si/P/Al oxotetrahedral framework in (iii) identifies a substituted aluminophosphate family (SAPO).
  • MgAl₂O₄ is the prototype spinel: Mg²⁺ occupies tetrahedral and Al³⁺ octahedral sites.
  • Hydroxyapatite is Ca₅(OH)(PO₄)₃; the printed formula omits the subscript 5 on Ca.

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), 2022 Mains Paper I: solution pages 1 and 2
Solution pages 1 and 2 of 28
Read the whole 2022 solution2022 question paper

Topic notes: main group chemistry: boranes, borazine, phosphazenes, silicates, silicones, interhalogens, xenon and sulfur–nitrogen compounds, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversorthosilicatecyclosilicate berylspinel MgAl2O4aluminophosphate SAPOhydroxyapatite

All parts of Question 1