UPSC Combined Geo-Scientist
Chemist
- 3 descriptive papers
- 200 marks each
- 3 h per paper
Mains Paper III covers analytical and organic chemistry.
Separation methods: every question, 2016 to 2025
32 parts worth 222 marks have been set on this unit in UPSC Geo-Scientist Chemistry Mains Paper III from 2016 to 2025. Each one opens on its own page with the question, the answer in brief and the key points.
Chromatographic analysis: basic principles of chromatography (partition, adsorption and ion exchange), column chromatography, plate concept, plate height (HETP), normal phase and reversed phase concept, thin layer chromatography, frontal analysis, principles of High Performance Liquid Chromatography (HPLC) and Gas Liquid Chromatography (GLC), and ion-exchange chromatography. Solvent extraction: classification, principle and efficiency of the technique, mechanism of extraction, extraction by solvation and chelation, qualitative and quantitative aspects of solvent extraction, extraction of metal ions from aqueous solutions.
Notes: Chromatography (HPLC, GLC, TLC, ion exchange) and solvent extraction (full notes) · short notes
2025
- Q1(b) van Deemter equation and its significance5 marks Answered
- Q2(a) Eluent composition for retention factor 5 in reversed-phase HPLC10 marks Answered
- Q2(b) Ion-exchange chromatography; retention on a strong acid resin15 marks Answered
2024
- Q1(b) Partition ratio k′ and relative retention α5 marks Answered
- Q2(a) Bonner affinity series of an ion-exchange resin10 marks Question only
- Q4(a) Plate height; number of plates from a chromatographic peak10 marks Answered
2023
- Q1(b) HPLC against GLC; particle size of packed GLC columns5 marks Answered
- Q2(b) Number of theoretical plates and HETP from a Gaussian peak10 marks Question only
- Q3(b) Craig counter-current distribution after three transfers10 marks Question only
2022
- Q1(b) Phases in GLC and choice of carrier gas5 marks Answered
- Q2(b) Resolution, plate number, plate height and a longer column10 marks Question only
- Q5(b) Fe(III) left after three extractions with ether10 marks Answered
2021
- Q1(e) Requirements of an extracting solvent5 marks Answered
- Q2(a) Rf value in thin layer chromatography10 marks Answered
- Q5(b) Extraction of Pb²⁺ as a chelate: the dithizone method5 marks Answered
2020
- Q1(b) Particle diameter in chromatography5 marks Answered
- Q2(b) Extraction of metal chelates10 marks Answered
- Q3(b) Temperature and pressure programming in GC5 marks Question only
- Q4(c)(i) Preparation and visualisation of TLC plates5 marks Answered
- Q4(c)(ii) Alumina as an adsorbent5 marks Answered
2019
- Q1(h) Gradient elution5 marks Answered
- Q4(f) TCD versus FID response5 marks Answered
2018
- Q1(e) Chromatographic zone broadening5 marks Answered
- Q1(h) Electron-capture selectivity5 marks Answered
- Q2(c) GLC and HPLC5 marks Question only
- Q4(b) Plate height10 marks Answered
2017
- Q1(f) Flame ionisation detector5 marks Answered
- Q3(a) Detectors used in HPLC10 marks Question only
- Q3(c) Cellulose powder and Sephadex gel: mechanisms and uses5 marks Question only
2016
- Q1(c) Solid-phase extraction4 marks Answered
- Q1(f) Butyric-acid extraction4 marks Answered
- Q1(h) HPLC and GLC4 marks Answered
UPSC Combined Geo-Scientist (Main) Chemistry Paper III: Model Answers 2021 to 2025
- All ten questions of each paper, with the question printed above its answer
- Instruments drawn as labelled diagrams, numericals worked with units
- Topic-wise weightage and a topic-wise index