UPSC Combined Geo-Scientist
Chemist
- 3 descriptive papers
- 200 marks each
- 3 h per paper
Mains Paper I covers inorganic chemistry.
Gravimetric analysis: every question, 2016 to 2025
24 parts worth 210 marks have been set on this unit in UPSC Geo-Scientist Chemistry Mains Paper I from 2016 to 2025. Each one opens on its own page with the question, the answer in brief and the key points.
General principles: solubility, solubility product and common ion effect, effect of temperature on the solubility; salt hydrolysis, hydrolysis constant, degree of hydrolysis. Stoichiometry, calculation of results from gravimetric data. Properties of precipitates. Nucleation and crystal growth, factors influencing completion of precipitation. Co-precipitation and post-precipitation, purification and washing of precipitates. Precipitation from homogeneous solution. A few common gravimetric estimations: chloride as silver chloride, sulphate as barium sulphate, aluminium as oxinate and nickel as dimethyl glyoximate.
Notes: Gravimetric analysis: solubility product, precipitation, co-precipitation, organic precipitants (full notes) · short notes
2025
- Q1(e) Solubility product of silver chromate5 marks Answered
- Q6(a) Sulphate as barium sulphate by the filtering-crucible method15 marks Answered
2024
- Q1(d) Silica by volatilisation gravimetry5 marks Answered
- Q5(c) Magnetite from an ignited iron oxide residue10 marks Answered
- Q6(a) Thermal decomposition of calcium oxalate15 marks Answered
- Q6(b) Organic precipitating reagents5 marks Answered
2023
- Q1(e) Solubility of lead phosphate5 marks Answered
- Q6(a)(i) Coprecipitation and postprecipitation10 marks Question only
- Q6(a)(ii) Oxine and aluminium oxinate5 marks Question only
- Q6(b) Nickel gravimetry with dimethylglyoxime15 marks Question only
2022
- Q1(e) Chloride from silver chloride5 marks Answered
- Q6(a) Lead, iron and copper in a rock10 marks Question only
- Q6(b) Nucleation and particle growth10 marks Question only
- Q6(c) Volatilisation gravimetry10 marks Question only
2021
- Q1(e) Postprecipitation versus coprecipitation5 marks Answered
- Q11(a) Controlling supersaturation in gravimetry10 marks Answered
- Q11(b) Peptisation and its prevention10 marks Answered
- Q11(c) Why excessive precipitant is avoided5 marks Answered
- Q11(d) Temperature and precipitate solubility5 marks Answered
2020
- Q1(d) Aluminium oxinate5 marks Answered
- Q5(c) Gravimetric nickel with dimethylglyoxime10 marks Question only
- Q6(a) Solubility versus solubility product10 marks Question only
- Q6(b) Co-precipitation and post-precipitation10 marks Question only
2019
- Q11(a) Selective sulfide precipitation15 marks Answered
UPSC Combined Geo-Scientist (Main) Chemistry Paper I: Model Answers 2021 to 2025
- All eleven questions of each paper, with the question printed above its answer
- Titration, gravimetric and nuclear numericals worked with units; structures drawn
- Topic-wise weightage and a topic-wise index