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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 · 2016 · Mains Paper III

Q1(g). DMG reagent requirement

Question

A 1.0 g steel sample contains 3% Ni. Find the volume of 1% w/w DMG in alcohol needed for 50% reagent excess. Use density 0.79 g/mL, M_(Ni)=58.69 and M_(DMG)=116.12.

Answer in brief

Approximately 22.54 mL of the DMG solution is required.

Key points

  • Nickel mass is 0.030 g, or 0.030/58.69=5.112×10⁻⁴ mol. Each nickel ion requires two DMG molecules.
  • Including 50% excess, n_(DMG)=1.5(2)(0.030/58.69) mol; reagent mass is 0.1781 g.
  • At 1% w/w this requires 17.81 g solution. Using the supplied density, V=17.81/0.79=22.54 mL.

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(g), 2016 Mains Paper III: solution pages 3 and 4
Solution pages 3 and 4 of 22
Read the whole 2016 solution2016 question paper

CoversDMG reagent requirementGravimetry

All parts of Question 1