UPSC Combined Geo-Scientist
Chemist
- 3 descriptive papers
- 200 marks each
- 3 h per paper
Mains Paper III covers analytical and organic chemistry.
All years
Pages 1 and 2 of 41 
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Mains Paper III, analytical and organic chemistry
Solution, 2024
UPSC Combined Geo-Scientist, Stage II (Mains). 41 pages. Questions 1, 4, 5, 6, 7 and 9 are answered.
Every question of 2024, one page each54 parts in 10 questions, with the question as text and the key points of its answer
Question 1 40 marks
- 1(a)Percentage relative error of a balance reading5 marks
- 1(b)Partition ratio k′ and relative retention α5 marks
- 1(c)Transmittance from Beer’s law5 marks
- 1(d)Identifying a magnesium compound from its thermogram5 marks
- 1(e)Properties needed in a detector for X-ray fluorescence5 marks
- 1(f)Generation of the plasma in the ICP torch5 marks
- 1(g)Calorific value of a fuel5 marks
- 1(h)AAS and ICP compared: accuracy, interferences, detection limit5 marks
Question 2 30 marks
Question 3 30 marks
Question 4 30 marks
Question 5 30 marks
Question 6 40 marks
- 6(a)Curtius rearrangement; the isocyanate closes to a cyclic urea4 marks
- 6(b)HBr and a conjugated diene: 1,2- and 1,4-addition4 marks
- 6(c)Phenylglycine and mandelic acid from benzaldehyde4 marks
- 6(d)Coumarin and 3-acetylcoumarin from salicylaldehyde4 marks
- 6(e)Intramolecular oxymercuration–demercuration: a cyclic ether4 marks
- 6(f)trans- and cis-Cyclohexane-1,2-diol from cyclohexanone4 marks
- 6(g)[1,5]-Carbon shift and Cope rearrangement4 marks
- 6(h)Four C₁₀H₁₄ isomers: the one marked by a McLafferty peak4 marks
- 6(i)C₃H₇NO with two N–methyl singlets: N,N-dimethylformamide4 marks
- 6(j)ν(C=C) of methylidenecycloalkanes and ring size4 marks
Question 7 30 marks
- 7(a)(i)Schmidt reaction of a cyclohexanone with an alkyl azide5 marks
- 7(a)(ii)Robinson annulation of 2-methylcyclohexane-1,3-dione5 marks
- 7(b)Oxepin: 6π electrocyclic ring closure, then Diels–Alder addition5 marks
- 7(c)Chloromethylation, then Sommelet–Hauser rearrangement5 marks
- 7(d)(i)Iodolactonisation of a cyclopentenylacetic acid5 marks
- 7(d)(ii)Epoxidation, then acid-catalysed ring expansion to a ketone5 marks
Question 8 30 marks
- 8(a)(i)2-Acetylbenzaldehyde with KCN: internal hydride shift to a lactone5 marks
- 8(a)(ii)Hydroboration–oxidation of norbornene: exo-norborneol5 marks
- 8(b)Photolysis of two ketones: Norrish Type II and Type I5 marks
- 8(c)Hexane-2,5-dione with acid: Paal–Knorr furan synthesis5 marks
- 8(d)Ozonolysis, then intramolecular aldol condensation10 marks
Question 9 30 marks
- 9(a)Structure from UV, IR, NMR and mass data: C₇H₈BrN10 marks
- 9(b)Dieckmann condensation, then hydrolysis and decarboxylation5 marks
- 9(c)Beer’s law for camphor; λmax of the methyl halides5 marks
- 9(d)(i)Birch reduction with ring closure: a spiro acid5 marks
- 9(d)(ii)Robinson annulation to a spiro enone5 marks
Question 10 30 marks
- 10(a)(i)Anisole with dibromocarbene: ring expansion to a tropone5 marks
- 10(a)(ii)Benzophenone with aluminium isopropoxide at 250 °C5 marks
- 10(b)Structure from ¹H and ¹³C NMR: C₁₅H₁₄O5 marks
- 10(c)Band width and colour; ν(C=O) of acids and ketones5 marks
- 10(d)(i)Mass spectral fragmentation of an ester and a cyclohexene5 marks
- 10(d)(ii)Structure from IR, ¹H and ¹³C NMR: C₁₀H₉NO₂5 marks
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Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
Model answer pages open with the VKC plan.
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Printed copy and Kindle
UPSC Combined Geo-Scientist (Main) Chemistry Paper III: Model Answers 2021 to 2025
The book has all five years of Paper III in one volume, with all ten questions of every paper answered, the question printed above each answer, a time plan for each paper, the topic-wise weightage of marks and a topic-wise index.