JEE Main 2021 · 22 July · evening · Single correct · +4 / −1
Sulphide ion is soft base and its ores are common for metals.
(a) Pb (b) Al (c) Ag (d) Mg
- (a) (a) and (c) only
- (b) (a) and (d) only
- (c) (a) and (b) only
- (d) (c) and (d) only
Answer and solution
Answer (a) (a) and (c) only
Solution
Chemistry ma’am · 3 steps
Soft likes soft: the sulphide ion, a soft base, binds the soft metal ions Pb²⁺ and Ag⁺.
- Hard and soft. By the HSAB principle, soft bases pair best with soft acids and hard bases pair best with hard acids. S²⁻ is large and easily polarised, so it is a soft base.
- Sort the cations. Small, highly charged ions such as Al³⁺ and Mg²⁺ are hard acids. They prefer hard bases like O²⁻, CO₃²⁻ and F⁻. Large, polarisable ions such as Pb²⁺ and Ag⁺ are soft acids.
Metal Ion Acid type Common ore Pb Pb²⁺ soft galena, PbS (sulphide) Al Al³⁺ hard bauxite, Al₂O₃ . xH₂O (oxide) Ag Ag⁺ soft argentite, Ag₂S (sulphide) Mg Mg²⁺ hard magnesite, MgCO₃ (carbonate) - So. Sulphide ores are common for Pb and Ag, which is option (a).
The idea to keep. Ore type follows HSAB: soft metal ions (Pb, Ag, Cu, Zn, Hg) are found as sulphides, while hard ions (Al, Mg, Ca, Na) are found as oxides, carbonates or halides.
Answer from the NTA final answer key. Solution by PrepWiser.