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UPSC Combined Geo-Scientist

Chemist

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

Mains Paper III covers analytical and organic chemistry.

UPSC Combined Geo-Scientist, Mains · 2021 · Mains Paper III

Q1(b). Ultimate analysis of coal

Question

What is the ultimate analysis of coal?

Answer in brief

The elemental analysis of coal: the mass percentages of carbon, hydrogen, nitrogen, sulfur and ash are determined, and oxygen is found by difference.

Key points

  • C and H: coal burnt in dry O₂; H₂O absorbed in weighed CaCl₂, CO₂ in weighed KOH bulbs.
  • N: Kjeldahl method; digestion with conc. H₂SO₄ gives (NH₄)₂SO₄, NH₃ liberated and absorbed in standard acid.
  • S: bomb washings or Eschka fusion hold sulfur as sulfate, precipitated and weighed as BaSO₄.
  • Ash: residue left when a weighed sample is burnt in a muffle furnace at 700–750 °C; oxygen is found by difference.

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), 2021 Mains Paper III: solution pages 3 and 4
Solution pages 3 and 4 of 39
Read the whole 2021 solution2021 question paper

Topic notes: analysis of ores, alloys, petroleum, coal and coke (dolomite, bauxite, brass, Ni in steel, aniline point, proximate and ultimate analysis, calorific value), with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversultimate analysis of coalelemental analysisKjeldahl methodEschka mixtureproximate analysis

All parts of Question 1