An aqueous solution of an unknown metal salt is subjected to qualitative analysis. When H ₂ S gas is passed through the solution in the presence of dilute HCl , no precipitate is observed. However, when H ₂ S gas is passed through the same solution after making it alkaline with NH ₄ OH in the presence of NH ₄ Cl , a distinct precipitate is formed. The metal cation present in the solution is:

Step-by-step solution

The qualitative analysis of cations relies on selective precipitation based on solubility products. Group II cations (such as Cu ²⁺ and Pb ²⁺ ) precipitate as sulphides when H ₂ S is passed in an acidic medium. Since no precipitate is formed in the acidic medium, Group II cations are absent. Group IV cations (such as Co ²⁺ , Ni ²⁺ , Mn ²⁺ , and Zn ²⁺ ) require a higher concentration of sulphide ions to precipitate. This is achieved by passing H ₂ S in an alkaline medium (using NH ₄ OH and NH ₄ Cl ). Since a precipi