Question

A substance X dissolves in hot conc. HCl to give solution which when treated with caustic soda solution gives a white ppt. which however dissolves in excess of caustic soda solution giving a strongly solution. On heating X with sulphur, a brown powder Y is formed which dissolved on warming with yellow ammonium sulphide solution. The solution gives a grey ppt. with HCl. When X is heated in air, a white powder Z is obtained which can be dissolved in conc. H₂SO₄ . When Z is fused with NaOH, extracted with hot water, then treated with mineral acid, white gelatinous ppt. is obtained. Identify X, Y, Z and give the reactions involved.

Answer 1

(i) Solution of X (with HCl) reacts with NaOH and forms white ppt.This ppt dissolves in excess of NaOH to give solution which has strongly reducing nature. This reducing properties of this solution points out that the solution might be containing sodium stannite and here X must be tin.

(ii) The nature of X as tin is confirmed by its reaction with S forming SnS₂ which dissolves in yellow ammonium sulphide but regenerates in presence of HCl. 

Thus the various reactions and nature of X, Y, and Z can be written as below