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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(c). Werner valencies and isomers

Question

A complex with the formula CoCl₃·4NH₃ gives precipitate with AgNO₃ with reference to one chloride ion. Answer the following: (i) What is the primary valency of cobalt? (ii) What is the secondary valency of cobalt? (iii) Draw the possible geometrical isomers of the compound.

Answer in brief

The formulation is [Co(NH₃)₄Cl₂]Cl: primary valency 3, secondary valency 6, with cis and trans isomers.

Key points

  • One chloride is outside the coordination sphere and gives one mole of AgCl per mole of complex: Ag⁺ + Cl⁻ → AgCl(s).
  • The remaining two chloride ions and four ammonia ligands are coordinated.
  • In the octahedral cis isomer the coordinated chlorides are adjacent, approximately 90° apart; in trans they are opposite, approximately 180° apart.

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(c), 2018 Mains Paper I: solution pages 3 and 4
Solution pages 3 and 4 of 17
Read the whole 2018 solution2018 question paper

CoversWerner valenciesisomersCoordination chemistry

All parts of Question 1