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.
Electrochemistry: every question, 2021 to 2025
15 parts worth 160 marks have been set on this unit in UPSC CSE Chemistry Paper I from 2021 to 2025. Each one opens on its own page with the question, the answer in brief and the key points.
Debye-Huckel theory of strong electrolytes and Debye-Huckel limiting law for various equilibrium and transport properties. Galvanic cells, concentration cells; electrochemical series, measurement of e.m.f. of cells and its applications; fuel cells and batteries. Processes at electrodes; double layer at the interface; rate of charge transfer, current density; overpotential; electroanalytical techniques: amperometry, ion selective electrodes and their uses.
Notes: Electrochemical cells: Nernst equation, emf and electrodes (full notes) · short notes
Notes: Electrolytes: conductance, Kohlrausch, Debye–Hückel and transport numbers (full notes) · short notes
Notes: Electrode kinetics: double layer, overpotential, Butler–Volmer and Tafel equations, polarography and voltammetry (full notes) · short notes
2025
- Q1(i) Time to plate a gold layer5 marks Answered
- Q2(b) Standard potential of O₂ reduction in base15 marks Answered
- Q4(b) Diffusion-limited current at an electrode10 marks Answered
- Q4(c) Molar conductivity and transport numbers of Ca(NO₃)₂10 marks Answered
2024
- Q1(d)(ii) Overvoltage and its applications5 marks Answered
- Q4(b)(i) Polarography and concentration polarisation15 marks Answered
- Q4(b)(ii) Concentration cells; fuel cells as energy converters5 marks Answered
2023
- Q1(e)(i) E° of Cr³⁺/Cr from two couples5 marks Answered
- Q3(c) Thermodynamics of the H₂–O₂ fuel cell20 marks Answered
2022
- Q1(e) ΔG° and K for the zinc–copper cell reaction10 marks Answered
- Q3(e) Forces on an ion moving through a strong-electrolyte solution10 marks Answered
- Q4(d) Principle of polarography; reading a polarogram10 marks Answered
2021
- Q1(e) Electrochemical series and its significance10 marks Answered
- Q3(b) Ion-selective electrodes; pH with the glass electrode20 marks Answered
- Q4(a) E.m.f. of a hydrogen–copper cell at 25 °C10 marks Answered
UPSC Civil Services (Main) Chemistry Paper I: Model Answers 2021 to 2025
- All eight questions of each paper, with the question printed above its answer
- Question choice and time plan for each paper
- Topic-wise weightage and a topic-wise index