UPSC Combined Geo-Scientist
Chemist
- 3 descriptive papers
- 200 marks each
- 3 h per paper
Mains Paper I covers inorganic chemistry.
All topics
Mains Paper I, inorganic chemistry
Acid-base titrations: every question, 2016 to 2025
22 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.
Syllabus
Titration curves for strong acid-strong base, weak acid-strong base and weak base-strong acid titrations, polyprotic acids, poly-equivalent bases, determining the equivalence point: theory of acid-base indicators, pH change range of indicator, selection of proper indicator. Principles used in estimation of mixtures of NaHCO₃ and Na₂CO₃ (by acidimetry).
Notes: Acid–base titrations: curves, indicators, buffers (full notes) · short notes
2025
- Q1(d) Phenolphthalein in dilute and in concentrated alkali5 marks Answered
- Q3(a) pH at the equivalence points of H₃PO₄ with KOH15 marks Answered
- Q3(b) Salt hydrolysis; sodium acetate, 0.01 M15 marks Answered
2024
- Q1(c) Choosing indicators5 marks Answered
- Q3(a) Reading a weak-acid titration curve15 marks Question only
- Q3(b) Criteria for a suitable indicator5 marks Question only
- Q3(c) Carbonate–bicarbonate mixtures10 marks Question only
2023
- Q1(d) Colour change of phenolphthalein5 marks Answered
- Q5(a) Two-stage titration of sodium carbonate15 marks Question only
- Q5(b) Acetic acid-NaOH titration curve15 marks Question only
2022
- Q1(d) Carbonate in carbonic acid5 marks Answered
- Q5(a) Strong acid-strong base titration10 marks Question only
- Q5(b) Phenolphthalein colour and fading10 marks Question only
- Q5(c) Weak base-strong acid titration10 marks Question only
2021
- Q1(d) Indicator choice for weak-acid titration5 marks Answered
- Q6(a) Acid required by an equimolar carbonate mixture10 marks Answered
- Q6(b) Methyl-red colour and ionisation10 marks Answered
- Q6(c) Weak diprotic base titrated with strong acid10 marks Answered
2020
- Q1(c) Boric acid titration5 marks Answered
- Q5(a) Indicator for HCl versus NH₄OH titration10 marks Question only
- Q5(b) Determining NaHCO₃ and Na₂CO₃ in a mixture10 marks Question only
2019
- Q2(a) Weak-acid titration indicator10 marks Answered
Printed copy and Kindle
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