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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 · 2023 · Mains Paper III

Q4(c). Potassium as ionisation suppressor for Sr in the N₂O–acetylene flame

Question

Sensitivity of Sr measurement by AAS is improved in N₂O-acetylene flame by adding K in the sample. Explain why.

Answer in brief

In the very hot flame part of the strontium is ionised and Sr⁺ does not absorb the atomic line; potassium ionises more easily, floods the flame with electrons and pushes Sr ⇌ Sr⁺ + e⁻ back to Sr atoms, so absorbance rises.

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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.

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Topic notes: spectroscopic instruments (Beer–Lambert law, UV–vis and IR instruments, Job's method, AAS and flame emission), with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversionisation interferenceionisation suppressorAASnitrous oxide acetylene flamestrontium

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