UPSC Combined Geo-Scientist, Mains · 2022 · Mains Paper I
Q1(e). Chloride from silver chloride
Question
A 25 mL solution containing Cl⁻ was treated with excess AgNO₃ solution to precipitate 0.830 g of AgCl. What was the molarity of Cl⁻ in the unknown solution? (At. wt. of Ag = 107.87, Cl = 35.453)
Answer in brief
The chloride concentration is 0.232 mol L⁻¹.
Key points
- Reaction: Ag⁺ + Cl⁻ → AgCl(s). The mole ratio Cl⁻ : AgCl is 1 : 1.
- M(AgCl) = 107.87 + 35.453 = 143.323 g mol⁻¹.
- n(Cl⁻) = 0.830/143.323 = 0.0057911 mol.
- [Cl⁻] = n/V = 0.0057911/0.025 = 0.23164 M ≈ 0.232 M, assuming quantitative recovery of pure, dry AgCl.
The full model answer
As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.
Coversgravimetric chlorideAgCl precipitatesilver nitratemolarity calculation
All parts of Question 1
- 1(a) Minerals and framework structures5 marks
- 1(b) Ground terms by L-S coupling5 marks
- 1(c) Square-planar stereoisomers5 marks
- 1(d) Carbonate in carbonic acid5 marks
- 1(e) Chloride from silver chloride5 marks
- 1(f) Iron percentage by permanganate5 marks
- 1(g) Masking copper to determine nickel5 marks
- 1(h) Carbonyl ligand counts5 marks
- 1(i) Carbon-14 dating of wood5 marks
- 1(j) Oxidising power across the series5 marks