UPSC Combined Geo-Scientist, Mains · 2022 · Mains Paper I
Q1(f). Iron percentage by permanganate
Question
A sample of 0.6128 g of iron ore is dissolved in HCl and all the iron is reduced to Fe²⁺ ions. This solution required 38.4 mL of 0.0198 M KMnO₄ to titrate under acidic conditions. Calculate the mass percent of iron in the ore. (Given atomic weight of iron = 55.85)
Answer in brief
Mass percentage of iron = 34.65%, or 34.6% to three significant figures.
Key points
- Balanced reaction: MnO₄⁻ + 8H⁺ + 5Fe²⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O.
- n(MnO₄⁻) = 0.0384 × 0.0198 = 7.6032 × 10⁻⁴ mol; n(Fe) = 5n(MnO₄⁻) = 0.0038016 mol.
- m(Fe) = 0.0038016 × 55.85 = 0.212327 g.
- % Fe = (0.212327/0.6128) × 100 = 34.647%, assuming all Fe is reduced and no other reductant consumes titrant.
- HCl introduces chloride; suppress its oxidation using suitable sulfuric-acid/Zimmermann-Reinhardt conditions before the permanganate titration.
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.
Coverspermanganometryiron ore estimationKMnO4 titrationZimmermann-Reinhardt
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