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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

Q5(e). Manganese in steel as permanganate: Beer's law

Question

0.55 g sample of an alloy steel was dissolved and its manganese content was oxidized to permanganate ion. The volume of the solution was diluted to 100 mL in a volumetric flask. The solution shows an absorbance of 0.42 at 530 nm due to MnO₄⁻ ion. Calculate the % of Mn in the alloy steel if path length is 1 cm and molar absorptivity for MnO₄⁻ ion is 4.2 × 10³ L mol⁻¹ cm⁻¹. [Atomic weight of Mn = 55]

Answer in brief

c(MnO₄⁻) = A/εb = 1.0 × 10⁻⁴ mol L⁻¹; Mn in 100 mL = 0.55 mg; Mn = 0.10 %.

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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 →

CoversBeer's lawmanganese in steelpermanganatespectrophotometric estimation

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