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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(e). Requirements of an extracting solvent

Question

Mention the requisite conditions of the extracting solvent to be fit for solvent extraction.

Answer in brief

The solvent must take up the wanted solute strongly and selectively (high D), be immiscible with water, separate quickly and cleanly, be inert, give the solute back easily, and be safe and cheap.

Key points

  • High distribution ratio D for the solute wanted and a low D for the impurities: efficient and selective extraction.
  • Immiscible with water: very low mutual solubility, so the two phases separate completely.
  • Density clearly different from water, low viscosity: layers separate quickly and no stable emulsion forms.
  • Chemically inert; easy recovery of the solute by evaporation or back-extraction.
  • Low toxicity and flammability, cheap; suited to the measurement that follows (e.g. MIBK in AAS).

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(e), 2021 Mains Paper III: solution pages 5 and 6
Solution pages 5 and 6 of 39
Read the whole 2021 solution2021 question paper

Topic notes: chromatography and solvent extraction (plates, resolution, van Deemter, HPLC, GLC, ion exchange, Craig), with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverssolvent extractiondistribution ratioextracting solventimmiscible solventMIBK

All parts of Question 1