Answer to Question #121973 in Inorganic Chemistry for Hussain Ousman Darboe

Question

Chlorine gas was passed over a heated substance X. A compound Y is formed which sublime in the tube. Substance Y is soluble in water and on adding sodium hydroxide a white precipitate is formed which is soluble in excess. A solution of Y also gives a white precipitate with ammonium which is soluble in excess. Suggest the nature of substances X and Y and explain the above reactions.

Answer 1

The fact that the substance Y is soluble in water and forms a white precipitate upon adding NaOH suggests that the compound Y is ionic, and, therefore, X is the metal and Y is the salt. If the white precipitate formed by the reaction of Y with NaOH and NH₄OH is soluble in excess of these bases, the complex compounds are formed. One of the metals which forms complexes in this case is zinc. Also zinc chloride is able to sublime partially. Zn(OH)₂ precipitate has white color. So the substance X is likely to be Zn, and substance Y - ZnCl₂. Reactions are following:

Zn(s)+ Cl₂(g)--> ZnCl₂(s)

ZnCl₂(aq) + 2NaOH(aq) --> Zn(OH)₂(s) + 2NaCl(aq)

Zn(OH)₂(s) + 2NaOH(aq) --> Na₂[Zn(OH)₄](aq)

ZnCl₂(aq) + 2NH₄OH(aq) --> Zn(OH)₂(s) + 2NH₄Cl(aq)

Zn(OH)₂(s) + 4NH₄OH(aq) --> [Zn(NH₃)₄](OH)₂(aq) + 4H₂O(l)