Chemistry - Salt Analysis Question with Solution | TestHub
A mixture of metal cations in an aqueous solution is subjected to the following sequence
1. Addition of dilute HCl gives precipitate (X1 ) and a filtrate with soluble metal ions.
2. Passing H2S in 0.3 M H3O+ through the filtrate produces precipitate ( X2)
3. Adding H2S in the presence of NH4OH to the next filtrate forms precipitate (X3 ) .
4. Addition of ammoniacal (NH4)2CO3 to the resulting filtrate yields precipitate (X4) ; remaining filtrate is (X5 ) .
In the above sequence, the colours of the precipitates (X1 ) , (X2 ) , (X3 ) , (X4) , and the colour of ion in (X5)aq can be, respectively.
Options:(select one or more)
Answer:
Solution:
The qualitative analysis scheme separates cations into groups based on their precipitation behavior.
1. Group I (HCl): Precipitate (X₁) is AgCl, PbCl₂, or Hg₂Cl₂ (white).
2. Group II (H₂S in acidic medium): Precipitate (X₂) includes sulfides like CuS (black), CdS (yellow), As₂S₃ (yellow), Sb₂S₃ (orange), SnS₂ (yellow), HgS (black), PbS (black), Bi₂S₃ (brown-black).
3. Group III (H₂S in ammoniacal medium): Precipitate (X₃) includes FeS (black), NiS (black), CoS (black), MnS (pink/flesh-colored), Al(OH)₃ (white gelatinous), Cr(OH)₃ (green gelatinous), ZnS (white).
4. Group IV ((NH₄)₂CO₃): Precipitate (X₄) includes carbonates like CaCO₃ (white), BaCO₃ (white), SrCO₃ (white).
5. Group V (Remaining filtrate X₅): Contains Na⁺, K⁺, NH₄⁺, Mg²⁺ (all colorless ions).
Analyzing the options:
A. White (X₁), Black (X₂), Green (X₃), White (X₄), Colourless (X₅). This is plausible (e.g., AgCl, CuS, Cr(OH)₃, CaCO₃, Na⁺).
B. White (X₁), Black (X₂), Pink (flesh-coloured) (X₃), White (X₄), Colourless (X₅). This is also plausible (e.g., AgCl, PbS, MnS, BaCO₃, K⁺).
Both options A and B present a valid sequence of precipitate colors based on common cations in each group.