Q10(b). Fluoride masking of aluminium
Show that F⁻ is an effective masking agent in preventing a reaction of Al³⁺ with EDTA. Assume that only significant forms of fluoride and EDTA are F⁻ and Y⁴⁻. (Given: (i) log K₁ = 6.11, log K₂ = 5.01, log K₃ = 3.88, log K₄ = 3.00, log K₅ = 1.4, log K₆ = 0.4 for the complexes between Al³⁺ and F⁻ and (ii) log K for the complex between EDTA and Al³⁺ = 16.3)
Model answer
The free solution for 2024 answers questions 1, 2, 5, 6, 9 and 11, the ones picked in its time plan. Question 10 is answered in full in the Geo-Scientist Chemistry Paper I, 2021 to 2025 book, with every part of every paper.
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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
Coversmasking agentfluoride maskingAl3+ EDTAstepwise stability constantsAlF6 3-
All parts of Question 10
- 10(a) Thermometric titration of Ca²⁺ and Mg²⁺10 marks
- 10(b) Fluoride masking of aluminium10 marks
- 10(c) Chelate effect and entropy10 marks