Hg2^2+ when reacts with H2S, black ppt. (A) formed which when reacts with Na2S followed by filtration leaving behind black ppt. (B). The filtrate with H+ gives black ppt. (C). A, B and C are:

Question

Prashant Kotian · Accepted Answer

Correct answer: C. Step 1: Cu2+ belongs to analytical Group II, while Fe2+ belongs to Group III/IV. Group II cations are selectively precipitated as sulfides in an acidic medium. Step 2: Passing H2S gas through a solution acidified with dil. HCl suppresses the sulfide ion concentration (common ion effect of H+), keeping it high enough to precipitate only the highly insoluble CuS (Ksp ~ 10^-36) while leaving Fe2+ in solution. Step 3: Thus, passing H2S in an acidic medium selectively precipitates copper(II) sulfide, separating it from Fe(II), corresponding to option (a).

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