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Indian Forest Service (Mains)

Chemistry optional

  • 2 papers
  • 200 marks each
  • 3 h per paper

Paper I covers physical and inorganic chemistry.

Indian Forest Service (Mains), Chemistry optional · 2023 · Paper I

Q1(e). Ionic atmosphere and electrode currents

Question

(i) What is meant by ionic atmosphere? How can we eliminate it? (ii) Differentiate between Faraday current and Diffusion current. (4+4 marks)

Answer in brief

The ionic atmosphere is a statistical excess of countercharge surrounding an ion. Faradaic current is caused by electrode redox; diffusion current is the part controlled by diffusive supply of electroactive species.

Key points

  • Opposite ions are on average enriched near a central ion, while like ions are depleted; their net distribution is the ionic atmosphere, not a fixed molecular shell.
  • Its effect vanishes at infinite dilution; a high-frequency field (Debye–Falkenhagen effect) or a very strong field (Wien effect) suppresses its effects.
  • Faradaic current involves electron transfer, such as Ox + ne⁻ → Red, and obeys Faraday's law; it differs from nonfaradaic double-layer charging current.
  • Diffusion current arises from a concentration gradient carrying electroactive material to the electrode: |id| = nFAD|dc/dx| at x = 0.
  • Therefore diffusion-controlled current is a kind of faradaic current, not its mutually exclusive alternative.

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), 2023 Paper I: solution pages 5 and 6
Solution pages 5 and 6 of 22
Read the whole 2023 solution2023 question paper

Topic notes: electrolytic conductance, Kohlrausch's law, transport numbers and the Debye–Hückel limiting law, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversionic atmosphereDebye–Falkenhagen effectWien effectfaradaic currentdiffusion current

All parts of Question 1