Indian Forest Service (Mains)
Chemistry optional
- 2 papers
- 200 marks each
- 3 h per paper
Paper I covers physical and inorganic chemistry.
Electrochemistry: every question, 2021 to 2025
16 parts worth 150 marks have been set on this unit in UPSC IFoS 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: voltammetry, polarography, amperometry, cyclic voltammetry, ion selective electrodes and their use.
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(e) Fast and slow electrode systems8 marks Answered
- Q4(b)(ii) Testing the stated activity-coefficient result10 marks Question only
- Q4(c)(i) Hydrogen and propane fuel cells10 marks Question only
- Q4(c)(ii) Competition between zinc deposition and hydrogen5 marks Question only
2024
- Q1(e) Aluminium–magnesium galvanic cell8 marks Answered
- Q2(d) Ordering metal reduction potentials5 marks Answered
- Q4(b) Mean ionic activity coefficients15 marks Answered
2023
- Q1(e) Ionic atmosphere and electrode currents8 marks Answered
- Q4(c) Cell voltage under load and electrolysis10 marks Answered
- Q4(d) Selective electrodes and ionic activity10 marks Answered
2022
- Q1(e) Activity coefficient of potassium ferricyanide8 marks Answered
- Q4(c)(i) Ionic atmosphere and mobility10 marks Answered
- Q4(c)(ii) pH from a quinhydrone cell5 marks Answered
2021
- Q1(e) Equilibrium constant of a Zn–Ag cell8 marks Answered
- Q3(c) Ion-selective and glass electrodes15 marks Question only
- Q4(a) Conductance and dilution of strong electrolytes15 marks Answered
UPSC Indian Forest Service (Main) Chemistry Paper I: Model Answers 2021 to 2025
- All eight questions of each paper, with the question printed above its answer
- Physical chemistry numericals worked with units; inorganic structures drawn
- Topic-wise weightage and a topic-wise index