Question:

Upon treatment with ammoniacal H2SH_2 S, the metal ion that precipitates as a sulphide is

Updated On: Jun 14, 2022
  • Fe (III)
  • Al(III)
  • Mg (II)
  • Zn(II)
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The Correct Option is D

Solution and Explanation

PLAN Ksp(ZnS)K_{sp} (ZnS) is very high and Zn2+Zn^{2+} is precipitated as ZnS by high concentration of S2S^{2-} formed when H2SH_2 S is passed in ammoniacal solution.
$\hspace20mm H_2 S \rightleftharpoons Zn^+ + S^{2-} \, (I)$
$\hspace10mm H^+ + OH^- \rightleftharpoons H_2 O \, (II)$
Reaction (I) is favoured in forward side if H+H^+ is removed immediately by OH(NH4OH)OH^- (NH_4 OH).
$\hspace10mm Zm^{2+} + S^{2-} \longrightarrow \, \underset{White \, ppt}{ \, ZnS\downarrow}$
Fe3+  and  AI3+Fe^{3+} \, \, and \, \, AI^{3+} are precipitated as hydroxide.
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