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UPSC Civil Services (Mains)

Chemistry optional

  • 2 papers
  • 250 marks each
  • 3 h per paper
  • 5 of 8 questions, Q1 and Q5 compulsory

Paper I covers physical and inorganic chemistry.

UPSC Civil Services (Mains), Chemistry optional · 2022 · Paper I

Q4(d). Principle of polarography; reading a polarogram

Question

Write down the basic principle of polarography. With the help of a neat typical polarogram discuss the significance of half-wave potential, diffusion current and limiting current.

Answer in brief

Polarography records the current through a dropping mercury electrode while the applied voltage is raised steadily; the S-shaped wave identifies an ion by its half-wave potential and gives its concentration from the diffusion current.

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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.

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Topic notes: electrode kinetics: the double layer, overpotential, the Butler–Volmer and Tafel equations, polarography and voltammetry, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverspolarographydropping mercury electrodehalf-wave potentialdiffusion currentIlkovič equationlimiting current

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