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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 · 2025 · Paper I

Q2(b). Standard potential of O₂ reduction in base

Question

The standard reduction potential of oxygen under acidic conditions at 298 K is 1.23 V. What is the standard reduction potential for the four-electron reduction of O₂(g) under basic conditions?

Answer in brief

E°(O₂/OH⁻) = +0.40 V at 298 K.

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Topic notes: electrochemical cells, Nernst equation and emf, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversstandard reduction potentialGibbs energy and EMFoxygen reduction in alkaline mediumionic product of waterNernst equation pH dependence

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