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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 · 2020 · Mains Paper I

Q1(b). Trans effect

Question

Explain Trans effect with suitable example.

Answer in brief

The trans effect is the kinetic ability of a coordinated ligand to accelerate substitution of the ligand opposite it, especially in square-planar complexes.

Key points

  • It concerns substitution rate, not simply the ground-state bond length (the related trans influence).
  • In Pt(II) chemistry, chloride has a stronger trans effect than ammonia. Starting from [PtCl₄]²⁻, the first ammonia gives [PtCl₃(NH₃)]⁻.
  • The second ammonia preferentially replaces a chloride trans to another chloride, rather than the chloride trans to ammonia.

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(b), 2020 Mains Paper I: solution pages 1 and 2
Solution pages 1 and 2 of 16
Read the whole 2020 solution2020 question paper

CoversTrans effectSquare-planar substitution

All parts of Question 1