Question

Alex was given a solution of an unknown salt Y for analysis. He performed the following tests and recorded his observations:
• To a part of the solution Y, he added silver nitrate solution and obtained a white precipitate which was soluble in ammonium hydroxide solution.
• To the remaining solution he added a few drops of sodium hydroxide solution and obtained a pale blue precipitate.
Based on the observations made by Alex, identify:
(a) the anion and
(b) the cation present in salt Y.

Hint:

Salt Y is Copper(II) Chloride (CuCl_2). Remember that while AgCl is soluble in NH_4OH, it is insoluble in dilute nitric acid!

Answer 1

(a) Anion: The anion is the Chloride ion (Cl^-). When silver nitrate is added to a chloride solution, it forms a white precipitate of Silver Chloride (AgCl) which dissolves in excess ammonium hydroxide to form a clear complex solution.
(b) Cation: The cation is the Copper(II) ion (Cu^2+). The formation of a pale blue precipitate (Copper(II) hydroxide) with sodium hydroxide is a characteristic test for copper ions.