Discussion Forum

Upon treatment with ammonical H₂S , the metal ion that precipitates as a sulphide is

Answer:

Explanation:

 Plan   K_sp(ZnS)   is very high and Zn²⁺  is precipitated as ZnS by high concentration of S^2-   formed when H₂S is  passed in ammoniacal  solution

   $H_{2}S\rightleftharpoons Zn^{+}+S^{2-}   $(I)

$H^{+}+OH^{-}\rightleftharpoons H_{2}O $(II)

Reaction (I) is favoured  in forward side if H⁺  is  removed immediately by OH^-  (NH₄OH)

$Zn^{2+}+S^{2-}\rightarrow ZnS\downarrow$

                                             white ppt.

 Fe³⁺  and Al³⁺  are precipitated as hydroxide